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diff --git a/Documentation/networking/bonding.txt b/Documentation/networking/bonding.txt new file mode 100644 index 000000000..83bf4986b --- /dev/null +++ b/Documentation/networking/bonding.txt @@ -0,0 +1,2743 @@ + + Linux Ethernet Bonding Driver HOWTO + + Latest update: 27 April 2011 + +Initial release : Thomas Davis <tadavis at lbl.gov> +Corrections, HA extensions : 2000/10/03-15 : + - Willy Tarreau <willy at meta-x.org> + - Constantine Gavrilov <const-g at xpert.com> + - Chad N. Tindel <ctindel at ieee dot org> + - Janice Girouard <girouard at us dot ibm dot com> + - Jay Vosburgh <fubar at us dot ibm dot com> + +Reorganized and updated Feb 2005 by Jay Vosburgh +Added Sysfs information: 2006/04/24 + - Mitch Williams <mitch.a.williams at intel.com> + +Introduction +============ + + The Linux bonding driver provides a method for aggregating +multiple network interfaces into a single logical "bonded" interface. +The behavior of the bonded interfaces depends upon the mode; generally +speaking, modes provide either hot standby or load balancing services. +Additionally, link integrity monitoring may be performed. + + The bonding driver originally came from Donald Becker's +beowulf patches for kernel 2.0. It has changed quite a bit since, and +the original tools from extreme-linux and beowulf sites will not work +with this version of the driver. + + For new versions of the driver, updated userspace tools, and +who to ask for help, please follow the links at the end of this file. + +Table of Contents +================= + +1. Bonding Driver Installation + +2. Bonding Driver Options + +3. Configuring Bonding Devices +3.1 Configuration with Sysconfig Support +3.1.1 Using DHCP with Sysconfig +3.1.2 Configuring Multiple Bonds with Sysconfig +3.2 Configuration with Initscripts Support +3.2.1 Using DHCP with Initscripts +3.2.2 Configuring Multiple Bonds with Initscripts +3.3 Configuring Bonding Manually with Ifenslave +3.3.1 Configuring Multiple Bonds Manually +3.4 Configuring Bonding Manually via Sysfs +3.5 Configuration with Interfaces Support +3.6 Overriding Configuration for Special Cases + +4. Querying Bonding Configuration +4.1 Bonding Configuration +4.2 Network Configuration + +5. Switch Configuration + +6. 802.1q VLAN Support + +7. Link Monitoring +7.1 ARP Monitor Operation +7.2 Configuring Multiple ARP Targets +7.3 MII Monitor Operation + +8. Potential Trouble Sources +8.1 Adventures in Routing +8.2 Ethernet Device Renaming +8.3 Painfully Slow Or No Failed Link Detection By Miimon + +9. SNMP agents + +10. Promiscuous mode + +11. Configuring Bonding for High Availability +11.1 High Availability in a Single Switch Topology +11.2 High Availability in a Multiple Switch Topology +11.2.1 HA Bonding Mode Selection for Multiple Switch Topology +11.2.2 HA Link Monitoring for Multiple Switch Topology + +12. Configuring Bonding for Maximum Throughput +12.1 Maximum Throughput in a Single Switch Topology +12.1.1 MT Bonding Mode Selection for Single Switch Topology +12.1.2 MT Link Monitoring for Single Switch Topology +12.2 Maximum Throughput in a Multiple Switch Topology +12.2.1 MT Bonding Mode Selection for Multiple Switch Topology +12.2.2 MT Link Monitoring for Multiple Switch Topology + +13. Switch Behavior Issues +13.1 Link Establishment and Failover Delays +13.2 Duplicated Incoming Packets + +14. Hardware Specific Considerations +14.1 IBM BladeCenter + +15. Frequently Asked Questions + +16. Resources and Links + + +1. Bonding Driver Installation +============================== + + Most popular distro kernels ship with the bonding driver +already available as a module. If your distro does not, or you +have need to compile bonding from source (e.g., configuring and +installing a mainline kernel from kernel.org), you'll need to perform +the following steps: + +1.1 Configure and build the kernel with bonding +----------------------------------------------- + + The current version of the bonding driver is available in the +drivers/net/bonding subdirectory of the most recent kernel source +(which is available on http://kernel.org). Most users "rolling their +own" will want to use the most recent kernel from kernel.org. + + Configure kernel with "make menuconfig" (or "make xconfig" or +"make config"), then select "Bonding driver support" in the "Network +device support" section. It is recommended that you configure the +driver as module since it is currently the only way to pass parameters +to the driver or configure more than one bonding device. + + Build and install the new kernel and modules. + +1.2 Bonding Control Utility +------------------------------------- + + It is recommended to configure bonding via iproute2 (netlink) +or sysfs, the old ifenslave control utility is obsolete. + +2. Bonding Driver Options +========================= + + Options for the bonding driver are supplied as parameters to the +bonding module at load time, or are specified via sysfs. + + Module options may be given as command line arguments to the +insmod or modprobe command, but are usually specified in either the +/etc/modrobe.d/*.conf configuration files, or in a distro-specific +configuration file (some of which are detailed in the next section). + + Details on bonding support for sysfs is provided in the +"Configuring Bonding Manually via Sysfs" section, below. + + The available bonding driver parameters are listed below. If a +parameter is not specified the default value is used. When initially +configuring a bond, it is recommended "tail -f /var/log/messages" be +run in a separate window to watch for bonding driver error messages. + + It is critical that either the miimon or arp_interval and +arp_ip_target parameters be specified, otherwise serious network +degradation will occur during link failures. Very few devices do not +support at least miimon, so there is really no reason not to use it. + + Options with textual values will accept either the text name +or, for backwards compatibility, the option value. E.g., +"mode=802.3ad" and "mode=4" set the same mode. + + The parameters are as follows: + +active_slave + + Specifies the new active slave for modes that support it + (active-backup, balance-alb and balance-tlb). Possible values + are the name of any currently enslaved interface, or an empty + string. If a name is given, the slave and its link must be up in order + to be selected as the new active slave. If an empty string is + specified, the current active slave is cleared, and a new active + slave is selected automatically. + + Note that this is only available through the sysfs interface. No module + parameter by this name exists. + + The normal value of this option is the name of the currently + active slave, or the empty string if there is no active slave or + the current mode does not use an active slave. + +ad_select + + Specifies the 802.3ad aggregation selection logic to use. The + possible values and their effects are: + + stable or 0 + + The active aggregator is chosen by largest aggregate + bandwidth. + + Reselection of the active aggregator occurs only when all + slaves of the active aggregator are down or the active + aggregator has no slaves. + + This is the default value. + + bandwidth or 1 + + The active aggregator is chosen by largest aggregate + bandwidth. Reselection occurs if: + + - A slave is added to or removed from the bond + + - Any slave's link state changes + + - Any slave's 802.3ad association state changes + + - The bond's administrative state changes to up + + count or 2 + + The active aggregator is chosen by the largest number of + ports (slaves). Reselection occurs as described under the + "bandwidth" setting, above. + + The bandwidth and count selection policies permit failover of + 802.3ad aggregations when partial failure of the active aggregator + occurs. This keeps the aggregator with the highest availability + (either in bandwidth or in number of ports) active at all times. + + This option was added in bonding version 3.4.0. + +all_slaves_active + + Specifies that duplicate frames (received on inactive ports) should be + dropped (0) or delivered (1). + + Normally, bonding will drop duplicate frames (received on inactive + ports), which is desirable for most users. But there are some times + it is nice to allow duplicate frames to be delivered. + + The default value is 0 (drop duplicate frames received on inactive + ports). + +arp_interval + + Specifies the ARP link monitoring frequency in milliseconds. + + The ARP monitor works by periodically checking the slave + devices to determine whether they have sent or received + traffic recently (the precise criteria depends upon the + bonding mode, and the state of the slave). Regular traffic is + generated via ARP probes issued for the addresses specified by + the arp_ip_target option. + + This behavior can be modified by the arp_validate option, + below. + + If ARP monitoring is used in an etherchannel compatible mode + (modes 0 and 2), the switch should be configured in a mode + that evenly distributes packets across all links. If the + switch is configured to distribute the packets in an XOR + fashion, all replies from the ARP targets will be received on + the same link which could cause the other team members to + fail. ARP monitoring should not be used in conjunction with + miimon. A value of 0 disables ARP monitoring. The default + value is 0. + +arp_ip_target + + Specifies the IP addresses to use as ARP monitoring peers when + arp_interval is > 0. These are the targets of the ARP request + sent to determine the health of the link to the targets. + Specify these values in ddd.ddd.ddd.ddd format. Multiple IP + addresses must be separated by a comma. At least one IP + address must be given for ARP monitoring to function. The + maximum number of targets that can be specified is 16. The + default value is no IP addresses. + +arp_validate + + Specifies whether or not ARP probes and replies should be + validated in any mode that supports arp monitoring, or whether + non-ARP traffic should be filtered (disregarded) for link + monitoring purposes. + + Possible values are: + + none or 0 + + No validation or filtering is performed. + + active or 1 + + Validation is performed only for the active slave. + + backup or 2 + + Validation is performed only for backup slaves. + + all or 3 + + Validation is performed for all slaves. + + filter or 4 + + Filtering is applied to all slaves. No validation is + performed. + + filter_active or 5 + + Filtering is applied to all slaves, validation is performed + only for the active slave. + + filter_backup or 6 + + Filtering is applied to all slaves, validation is performed + only for backup slaves. + + Validation: + + Enabling validation causes the ARP monitor to examine the incoming + ARP requests and replies, and only consider a slave to be up if it + is receiving the appropriate ARP traffic. + + For an active slave, the validation checks ARP replies to confirm + that they were generated by an arp_ip_target. Since backup slaves + do not typically receive these replies, the validation performed + for backup slaves is on the broadcast ARP request sent out via the + active slave. It is possible that some switch or network + configurations may result in situations wherein the backup slaves + do not receive the ARP requests; in such a situation, validation + of backup slaves must be disabled. + + The validation of ARP requests on backup slaves is mainly helping + bonding to decide which slaves are more likely to work in case of + the active slave failure, it doesn't really guarantee that the + backup slave will work if it's selected as the next active slave. + + Validation is useful in network configurations in which multiple + bonding hosts are concurrently issuing ARPs to one or more targets + beyond a common switch. Should the link between the switch and + target fail (but not the switch itself), the probe traffic + generated by the multiple bonding instances will fool the standard + ARP monitor into considering the links as still up. Use of + validation can resolve this, as the ARP monitor will only consider + ARP requests and replies associated with its own instance of + bonding. + + Filtering: + + Enabling filtering causes the ARP monitor to only use incoming ARP + packets for link availability purposes. Arriving packets that are + not ARPs are delivered normally, but do not count when determining + if a slave is available. + + Filtering operates by only considering the reception of ARP + packets (any ARP packet, regardless of source or destination) when + determining if a slave has received traffic for link availability + purposes. + + Filtering is useful in network configurations in which significant + levels of third party broadcast traffic would fool the standard + ARP monitor into considering the links as still up. Use of + filtering can resolve this, as only ARP traffic is considered for + link availability purposes. + + This option was added in bonding version 3.1.0. + +arp_all_targets + + Specifies the quantity of arp_ip_targets that must be reachable + in order for the ARP monitor to consider a slave as being up. + This option affects only active-backup mode for slaves with + arp_validation enabled. + + Possible values are: + + any or 0 + + consider the slave up only when any of the arp_ip_targets + is reachable + + all or 1 + + consider the slave up only when all of the arp_ip_targets + are reachable + +downdelay + + Specifies the time, in milliseconds, to wait before disabling + a slave after a link failure has been detected. This option + is only valid for the miimon link monitor. The downdelay + value should be a multiple of the miimon value; if not, it + will be rounded down to the nearest multiple. The default + value is 0. + +fail_over_mac + + Specifies whether active-backup mode should set all slaves to + the same MAC address at enslavement (the traditional + behavior), or, when enabled, perform special handling of the + bond's MAC address in accordance with the selected policy. + + Possible values are: + + none or 0 + + This setting disables fail_over_mac, and causes + bonding to set all slaves of an active-backup bond to + the same MAC address at enslavement time. This is the + default. + + active or 1 + + The "active" fail_over_mac policy indicates that the + MAC address of the bond should always be the MAC + address of the currently active slave. The MAC + address of the slaves is not changed; instead, the MAC + address of the bond changes during a failover. + + This policy is useful for devices that cannot ever + alter their MAC address, or for devices that refuse + incoming broadcasts with their own source MAC (which + interferes with the ARP monitor). + + The down side of this policy is that every device on + the network must be updated via gratuitous ARP, + vs. just updating a switch or set of switches (which + often takes place for any traffic, not just ARP + traffic, if the switch snoops incoming traffic to + update its tables) for the traditional method. If the + gratuitous ARP is lost, communication may be + disrupted. + + When this policy is used in conjunction with the mii + monitor, devices which assert link up prior to being + able to actually transmit and receive are particularly + susceptible to loss of the gratuitous ARP, and an + appropriate updelay setting may be required. + + follow or 2 + + The "follow" fail_over_mac policy causes the MAC + address of the bond to be selected normally (normally + the MAC address of the first slave added to the bond). + However, the second and subsequent slaves are not set + to this MAC address while they are in a backup role; a + slave is programmed with the bond's MAC address at + failover time (and the formerly active slave receives + the newly active slave's MAC address). + + This policy is useful for multiport devices that + either become confused or incur a performance penalty + when multiple ports are programmed with the same MAC + address. + + + The default policy is none, unless the first slave cannot + change its MAC address, in which case the active policy is + selected by default. + + This option may be modified via sysfs only when no slaves are + present in the bond. + + This option was added in bonding version 3.2.0. The "follow" + policy was added in bonding version 3.3.0. + +lacp_rate + + Option specifying the rate in which we'll ask our link partner + to transmit LACPDU packets in 802.3ad mode. Possible values + are: + + slow or 0 + Request partner to transmit LACPDUs every 30 seconds + + fast or 1 + Request partner to transmit LACPDUs every 1 second + + The default is slow. + +max_bonds + + Specifies the number of bonding devices to create for this + instance of the bonding driver. E.g., if max_bonds is 3, and + the bonding driver is not already loaded, then bond0, bond1 + and bond2 will be created. The default value is 1. Specifying + a value of 0 will load bonding, but will not create any devices. + +miimon + + Specifies the MII link monitoring frequency in milliseconds. + This determines how often the link state of each slave is + inspected for link failures. A value of zero disables MII + link monitoring. A value of 100 is a good starting point. + The use_carrier option, below, affects how the link state is + determined. See the High Availability section for additional + information. The default value is 0. + +min_links + + Specifies the minimum number of links that must be active before + asserting carrier. It is similar to the Cisco EtherChannel min-links + feature. This allows setting the minimum number of member ports that + must be up (link-up state) before marking the bond device as up + (carrier on). This is useful for situations where higher level services + such as clustering want to ensure a minimum number of low bandwidth + links are active before switchover. This option only affect 802.3ad + mode. + + The default value is 0. This will cause carrier to be asserted (for + 802.3ad mode) whenever there is an active aggregator, regardless of the + number of available links in that aggregator. Note that, because an + aggregator cannot be active without at least one available link, + setting this option to 0 or to 1 has the exact same effect. + +mode + + Specifies one of the bonding policies. The default is + balance-rr (round robin). Possible values are: + + balance-rr or 0 + + Round-robin policy: Transmit packets in sequential + order from the first available slave through the + last. This mode provides load balancing and fault + tolerance. + + active-backup or 1 + + Active-backup policy: Only one slave in the bond is + active. A different slave becomes active if, and only + if, the active slave fails. The bond's MAC address is + externally visible on only one port (network adapter) + to avoid confusing the switch. + + In bonding version 2.6.2 or later, when a failover + occurs in active-backup mode, bonding will issue one + or more gratuitous ARPs on the newly active slave. + One gratuitous ARP is issued for the bonding master + interface and each VLAN interfaces configured above + it, provided that the interface has at least one IP + address configured. Gratuitous ARPs issued for VLAN + interfaces are tagged with the appropriate VLAN id. + + This mode provides fault tolerance. The primary + option, documented below, affects the behavior of this + mode. + + balance-xor or 2 + + XOR policy: Transmit based on the selected transmit + hash policy. The default policy is a simple [(source + MAC address XOR'd with destination MAC address XOR + packet type ID) modulo slave count]. Alternate transmit + policies may be selected via the xmit_hash_policy option, + described below. + + This mode provides load balancing and fault tolerance. + + broadcast or 3 + + Broadcast policy: transmits everything on all slave + interfaces. This mode provides fault tolerance. + + 802.3ad or 4 + + IEEE 802.3ad Dynamic link aggregation. Creates + aggregation groups that share the same speed and + duplex settings. Utilizes all slaves in the active + aggregator according to the 802.3ad specification. + + Slave selection for outgoing traffic is done according + to the transmit hash policy, which may be changed from + the default simple XOR policy via the xmit_hash_policy + option, documented below. Note that not all transmit + policies may be 802.3ad compliant, particularly in + regards to the packet mis-ordering requirements of + section 43.2.4 of the 802.3ad standard. Differing + peer implementations will have varying tolerances for + noncompliance. + + Prerequisites: + + 1. Ethtool support in the base drivers for retrieving + the speed and duplex of each slave. + + 2. A switch that supports IEEE 802.3ad Dynamic link + aggregation. + + Most switches will require some type of configuration + to enable 802.3ad mode. + + balance-tlb or 5 + + Adaptive transmit load balancing: channel bonding that + does not require any special switch support. + + In tlb_dynamic_lb=1 mode; the outgoing traffic is + distributed according to the current load (computed + relative to the speed) on each slave. + + In tlb_dynamic_lb=0 mode; the load balancing based on + current load is disabled and the load is distributed + only using the hash distribution. + + Incoming traffic is received by the current slave. + If the receiving slave fails, another slave takes over + the MAC address of the failed receiving slave. + + Prerequisite: + + Ethtool support in the base drivers for retrieving the + speed of each slave. + + balance-alb or 6 + + Adaptive load balancing: includes balance-tlb plus + receive load balancing (rlb) for IPV4 traffic, and + does not require any special switch support. The + receive load balancing is achieved by ARP negotiation. + The bonding driver intercepts the ARP Replies sent by + the local system on their way out and overwrites the + source hardware address with the unique hardware + address of one of the slaves in the bond such that + different peers use different hardware addresses for + the server. + + Receive traffic from connections created by the server + is also balanced. When the local system sends an ARP + Request the bonding driver copies and saves the peer's + IP information from the ARP packet. When the ARP + Reply arrives from the peer, its hardware address is + retrieved and the bonding driver initiates an ARP + reply to this peer assigning it to one of the slaves + in the bond. A problematic outcome of using ARP + negotiation for balancing is that each time that an + ARP request is broadcast it uses the hardware address + of the bond. Hence, peers learn the hardware address + of the bond and the balancing of receive traffic + collapses to the current slave. This is handled by + sending updates (ARP Replies) to all the peers with + their individually assigned hardware address such that + the traffic is redistributed. Receive traffic is also + redistributed when a new slave is added to the bond + and when an inactive slave is re-activated. The + receive load is distributed sequentially (round robin) + among the group of highest speed slaves in the bond. + + When a link is reconnected or a new slave joins the + bond the receive traffic is redistributed among all + active slaves in the bond by initiating ARP Replies + with the selected MAC address to each of the + clients. The updelay parameter (detailed below) must + be set to a value equal or greater than the switch's + forwarding delay so that the ARP Replies sent to the + peers will not be blocked by the switch. + + Prerequisites: + + 1. Ethtool support in the base drivers for retrieving + the speed of each slave. + + 2. Base driver support for setting the hardware + address of a device while it is open. This is + required so that there will always be one slave in the + team using the bond hardware address (the + curr_active_slave) while having a unique hardware + address for each slave in the bond. If the + curr_active_slave fails its hardware address is + swapped with the new curr_active_slave that was + chosen. + +num_grat_arp +num_unsol_na + + Specify the number of peer notifications (gratuitous ARPs and + unsolicited IPv6 Neighbor Advertisements) to be issued after a + failover event. As soon as the link is up on the new slave + (possibly immediately) a peer notification is sent on the + bonding device and each VLAN sub-device. This is repeated at + each link monitor interval (arp_interval or miimon, whichever + is active) if the number is greater than 1. + + The valid range is 0 - 255; the default value is 1. These options + affect only the active-backup mode. These options were added for + bonding versions 3.3.0 and 3.4.0 respectively. + + From Linux 3.0 and bonding version 3.7.1, these notifications + are generated by the ipv4 and ipv6 code and the numbers of + repetitions cannot be set independently. + +packets_per_slave + + Specify the number of packets to transmit through a slave before + moving to the next one. When set to 0 then a slave is chosen at + random. + + The valid range is 0 - 65535; the default value is 1. This option + has effect only in balance-rr mode. + +primary + + A string (eth0, eth2, etc) specifying which slave is the + primary device. The specified device will always be the + active slave while it is available. Only when the primary is + off-line will alternate devices be used. This is useful when + one slave is preferred over another, e.g., when one slave has + higher throughput than another. + + The primary option is only valid for active-backup(1), + balance-tlb (5) and balance-alb (6) mode. + +primary_reselect + + Specifies the reselection policy for the primary slave. This + affects how the primary slave is chosen to become the active slave + when failure of the active slave or recovery of the primary slave + occurs. This option is designed to prevent flip-flopping between + the primary slave and other slaves. Possible values are: + + always or 0 (default) + + The primary slave becomes the active slave whenever it + comes back up. + + better or 1 + + The primary slave becomes the active slave when it comes + back up, if the speed and duplex of the primary slave is + better than the speed and duplex of the current active + slave. + + failure or 2 + + The primary slave becomes the active slave only if the + current active slave fails and the primary slave is up. + + The primary_reselect setting is ignored in two cases: + + If no slaves are active, the first slave to recover is + made the active slave. + + When initially enslaved, the primary slave is always made + the active slave. + + Changing the primary_reselect policy via sysfs will cause an + immediate selection of the best active slave according to the new + policy. This may or may not result in a change of the active + slave, depending upon the circumstances. + + This option was added for bonding version 3.6.0. + +tlb_dynamic_lb + + Specifies if dynamic shuffling of flows is enabled in tlb + mode. The value has no effect on any other modes. + + The default behavior of tlb mode is to shuffle active flows across + slaves based on the load in that interval. This gives nice lb + characteristics but can cause packet reordering. If re-ordering is + a concern use this variable to disable flow shuffling and rely on + load balancing provided solely by the hash distribution. + xmit-hash-policy can be used to select the appropriate hashing for + the setup. + + The sysfs entry can be used to change the setting per bond device + and the initial value is derived from the module parameter. The + sysfs entry is allowed to be changed only if the bond device is + down. + + The default value is "1" that enables flow shuffling while value "0" + disables it. This option was added in bonding driver 3.7.1 + + +updelay + + Specifies the time, in milliseconds, to wait before enabling a + slave after a link recovery has been detected. This option is + only valid for the miimon link monitor. The updelay value + should be a multiple of the miimon value; if not, it will be + rounded down to the nearest multiple. The default value is 0. + +use_carrier + + Specifies whether or not miimon should use MII or ETHTOOL + ioctls vs. netif_carrier_ok() to determine the link + status. The MII or ETHTOOL ioctls are less efficient and + utilize a deprecated calling sequence within the kernel. The + netif_carrier_ok() relies on the device driver to maintain its + state with netif_carrier_on/off; at this writing, most, but + not all, device drivers support this facility. + + If bonding insists that the link is up when it should not be, + it may be that your network device driver does not support + netif_carrier_on/off. The default state for netif_carrier is + "carrier on," so if a driver does not support netif_carrier, + it will appear as if the link is always up. In this case, + setting use_carrier to 0 will cause bonding to revert to the + MII / ETHTOOL ioctl method to determine the link state. + + A value of 1 enables the use of netif_carrier_ok(), a value of + 0 will use the deprecated MII / ETHTOOL ioctls. The default + value is 1. + +xmit_hash_policy + + Selects the transmit hash policy to use for slave selection in + balance-xor, 802.3ad, and tlb modes. Possible values are: + + layer2 + + Uses XOR of hardware MAC addresses and packet type ID + field to generate the hash. The formula is + + hash = source MAC XOR destination MAC XOR packet type ID + slave number = hash modulo slave count + + This algorithm will place all traffic to a particular + network peer on the same slave. + + This algorithm is 802.3ad compliant. + + layer2+3 + + This policy uses a combination of layer2 and layer3 + protocol information to generate the hash. + + Uses XOR of hardware MAC addresses and IP addresses to + generate the hash. The formula is + + hash = source MAC XOR destination MAC XOR packet type ID + hash = hash XOR source IP XOR destination IP + hash = hash XOR (hash RSHIFT 16) + hash = hash XOR (hash RSHIFT 8) + And then hash is reduced modulo slave count. + + If the protocol is IPv6 then the source and destination + addresses are first hashed using ipv6_addr_hash. + + This algorithm will place all traffic to a particular + network peer on the same slave. For non-IP traffic, + the formula is the same as for the layer2 transmit + hash policy. + + This policy is intended to provide a more balanced + distribution of traffic than layer2 alone, especially + in environments where a layer3 gateway device is + required to reach most destinations. + + This algorithm is 802.3ad compliant. + + layer3+4 + + This policy uses upper layer protocol information, + when available, to generate the hash. This allows for + traffic to a particular network peer to span multiple + slaves, although a single connection will not span + multiple slaves. + + The formula for unfragmented TCP and UDP packets is + + hash = source port, destination port (as in the header) + hash = hash XOR source IP XOR destination IP + hash = hash XOR (hash RSHIFT 16) + hash = hash XOR (hash RSHIFT 8) + And then hash is reduced modulo slave count. + + If the protocol is IPv6 then the source and destination + addresses are first hashed using ipv6_addr_hash. + + For fragmented TCP or UDP packets and all other IPv4 and + IPv6 protocol traffic, the source and destination port + information is omitted. For non-IP traffic, the + formula is the same as for the layer2 transmit hash + policy. + + This algorithm is not fully 802.3ad compliant. A + single TCP or UDP conversation containing both + fragmented and unfragmented packets will see packets + striped across two interfaces. This may result in out + of order delivery. Most traffic types will not meet + this criteria, as TCP rarely fragments traffic, and + most UDP traffic is not involved in extended + conversations. Other implementations of 802.3ad may + or may not tolerate this noncompliance. + + encap2+3 + + This policy uses the same formula as layer2+3 but it + relies on skb_flow_dissect to obtain the header fields + which might result in the use of inner headers if an + encapsulation protocol is used. For example this will + improve the performance for tunnel users because the + packets will be distributed according to the encapsulated + flows. + + encap3+4 + + This policy uses the same formula as layer3+4 but it + relies on skb_flow_dissect to obtain the header fields + which might result in the use of inner headers if an + encapsulation protocol is used. For example this will + improve the performance for tunnel users because the + packets will be distributed according to the encapsulated + flows. + + The default value is layer2. This option was added in bonding + version 2.6.3. In earlier versions of bonding, this parameter + does not exist, and the layer2 policy is the only policy. The + layer2+3 value was added for bonding version 3.2.2. + +resend_igmp + + Specifies the number of IGMP membership reports to be issued after + a failover event. One membership report is issued immediately after + the failover, subsequent packets are sent in each 200ms interval. + + The valid range is 0 - 255; the default value is 1. A value of 0 + prevents the IGMP membership report from being issued in response + to the failover event. + + This option is useful for bonding modes balance-rr (0), active-backup + (1), balance-tlb (5) and balance-alb (6), in which a failover can + switch the IGMP traffic from one slave to another. Therefore a fresh + IGMP report must be issued to cause the switch to forward the incoming + IGMP traffic over the newly selected slave. + + This option was added for bonding version 3.7.0. + +lp_interval + + Specifies the number of seconds between instances where the bonding + driver sends learning packets to each slaves peer switch. + + The valid range is 1 - 0x7fffffff; the default value is 1. This Option + has effect only in balance-tlb and balance-alb modes. + +3. Configuring Bonding Devices +============================== + + You can configure bonding using either your distro's network +initialization scripts, or manually using either iproute2 or the +sysfs interface. Distros generally use one of three packages for the +network initialization scripts: initscripts, sysconfig or interfaces. +Recent versions of these packages have support for bonding, while older +versions do not. + + We will first describe the options for configuring bonding for +distros using versions of initscripts, sysconfig and interfaces with full +or partial support for bonding, then provide information on enabling +bonding without support from the network initialization scripts (i.e., +older versions of initscripts or sysconfig). + + If you're unsure whether your distro uses sysconfig, +initscripts or interfaces, or don't know if it's new enough, have no fear. +Determining this is fairly straightforward. + + First, look for a file called interfaces in /etc/network directory. +If this file is present in your system, then your system use interfaces. See +Configuration with Interfaces Support. + + Else, issue the command: + +$ rpm -qf /sbin/ifup + + It will respond with a line of text starting with either +"initscripts" or "sysconfig," followed by some numbers. This is the +package that provides your network initialization scripts. + + Next, to determine if your installation supports bonding, +issue the command: + +$ grep ifenslave /sbin/ifup + + If this returns any matches, then your initscripts or +sysconfig has support for bonding. + +3.1 Configuration with Sysconfig Support +---------------------------------------- + + This section applies to distros using a version of sysconfig +with bonding support, for example, SuSE Linux Enterprise Server 9. + + SuSE SLES 9's networking configuration system does support +bonding, however, at this writing, the YaST system configuration +front end does not provide any means to work with bonding devices. +Bonding devices can be managed by hand, however, as follows. + + First, if they have not already been configured, configure the +slave devices. On SLES 9, this is most easily done by running the +yast2 sysconfig configuration utility. The goal is for to create an +ifcfg-id file for each slave device. The simplest way to accomplish +this is to configure the devices for DHCP (this is only to get the +file ifcfg-id file created; see below for some issues with DHCP). The +name of the configuration file for each device will be of the form: + +ifcfg-id-xx:xx:xx:xx:xx:xx + + Where the "xx" portion will be replaced with the digits from +the device's permanent MAC address. + + Once the set of ifcfg-id-xx:xx:xx:xx:xx:xx files has been +created, it is necessary to edit the configuration files for the slave +devices (the MAC addresses correspond to those of the slave devices). +Before editing, the file will contain multiple lines, and will look +something like this: + +BOOTPROTO='dhcp' +STARTMODE='on' +USERCTL='no' +UNIQUE='XNzu.WeZGOGF+4wE' +_nm_name='bus-pci-0001:61:01.0' + + Change the BOOTPROTO and STARTMODE lines to the following: + +BOOTPROTO='none' +STARTMODE='off' + + Do not alter the UNIQUE or _nm_name lines. Remove any other +lines (USERCTL, etc). + + Once the ifcfg-id-xx:xx:xx:xx:xx:xx files have been modified, +it's time to create the configuration file for the bonding device +itself. This file is named ifcfg-bondX, where X is the number of the +bonding device to create, starting at 0. The first such file is +ifcfg-bond0, the second is ifcfg-bond1, and so on. The sysconfig +network configuration system will correctly start multiple instances +of bonding. + + The contents of the ifcfg-bondX file is as follows: + +BOOTPROTO="static" +BROADCAST="10.0.2.255" +IPADDR="10.0.2.10" +NETMASK="255.255.0.0" +NETWORK="10.0.2.0" +REMOTE_IPADDR="" +STARTMODE="onboot" +BONDING_MASTER="yes" +BONDING_MODULE_OPTS="mode=active-backup miimon=100" +BONDING_SLAVE0="eth0" +BONDING_SLAVE1="bus-pci-0000:06:08.1" + + Replace the sample BROADCAST, IPADDR, NETMASK and NETWORK +values with the appropriate values for your network. + + The STARTMODE specifies when the device is brought online. +The possible values are: + + onboot: The device is started at boot time. If you're not + sure, this is probably what you want. + + manual: The device is started only when ifup is called + manually. Bonding devices may be configured this + way if you do not wish them to start automatically + at boot for some reason. + + hotplug: The device is started by a hotplug event. This is not + a valid choice for a bonding device. + + off or ignore: The device configuration is ignored. + + The line BONDING_MASTER='yes' indicates that the device is a +bonding master device. The only useful value is "yes." + + The contents of BONDING_MODULE_OPTS are supplied to the +instance of the bonding module for this device. Specify the options +for the bonding mode, link monitoring, and so on here. Do not include +the max_bonds bonding parameter; this will confuse the configuration +system if you have multiple bonding devices. + + Finally, supply one BONDING_SLAVEn="slave device" for each +slave. where "n" is an increasing value, one for each slave. The +"slave device" is either an interface name, e.g., "eth0", or a device +specifier for the network device. The interface name is easier to +find, but the ethN names are subject to change at boot time if, e.g., +a device early in the sequence has failed. The device specifiers +(bus-pci-0000:06:08.1 in the example above) specify the physical +network device, and will not change unless the device's bus location +changes (for example, it is moved from one PCI slot to another). The +example above uses one of each type for demonstration purposes; most +configurations will choose one or the other for all slave devices. + + When all configuration files have been modified or created, +networking must be restarted for the configuration changes to take +effect. This can be accomplished via the following: + +# /etc/init.d/network restart + + Note that the network control script (/sbin/ifdown) will +remove the bonding module as part of the network shutdown processing, +so it is not necessary to remove the module by hand if, e.g., the +module parameters have changed. + + Also, at this writing, YaST/YaST2 will not manage bonding +devices (they do not show bonding interfaces on its list of network +devices). It is necessary to edit the configuration file by hand to +change the bonding configuration. + + Additional general options and details of the ifcfg file +format can be found in an example ifcfg template file: + +/etc/sysconfig/network/ifcfg.template + + Note that the template does not document the various BONDING_ +settings described above, but does describe many of the other options. + +3.1.1 Using DHCP with Sysconfig +------------------------------- + + Under sysconfig, configuring a device with BOOTPROTO='dhcp' +will cause it to query DHCP for its IP address information. At this +writing, this does not function for bonding devices; the scripts +attempt to obtain the device address from DHCP prior to adding any of +the slave devices. Without active slaves, the DHCP requests are not +sent to the network. + +3.1.2 Configuring Multiple Bonds with Sysconfig +----------------------------------------------- + + The sysconfig network initialization system is capable of +handling multiple bonding devices. All that is necessary is for each +bonding instance to have an appropriately configured ifcfg-bondX file +(as described above). Do not specify the "max_bonds" parameter to any +instance of bonding, as this will confuse sysconfig. If you require +multiple bonding devices with identical parameters, create multiple +ifcfg-bondX files. + + Because the sysconfig scripts supply the bonding module +options in the ifcfg-bondX file, it is not necessary to add them to +the system /etc/modules.d/*.conf configuration files. + +3.2 Configuration with Initscripts Support +------------------------------------------ + + This section applies to distros using a recent version of +initscripts with bonding support, for example, Red Hat Enterprise Linux +version 3 or later, Fedora, etc. On these systems, the network +initialization scripts have knowledge of bonding, and can be configured to +control bonding devices. Note that older versions of the initscripts +package have lower levels of support for bonding; this will be noted where +applicable. + + These distros will not automatically load the network adapter +driver unless the ethX device is configured with an IP address. +Because of this constraint, users must manually configure a +network-script file for all physical adapters that will be members of +a bondX link. Network script files are located in the directory: + +/etc/sysconfig/network-scripts + + The file name must be prefixed with "ifcfg-eth" and suffixed +with the adapter's physical adapter number. For example, the script +for eth0 would be named /etc/sysconfig/network-scripts/ifcfg-eth0. +Place the following text in the file: + +DEVICE=eth0 +USERCTL=no +ONBOOT=yes +MASTER=bond0 +SLAVE=yes +BOOTPROTO=none + + The DEVICE= line will be different for every ethX device and +must correspond with the name of the file, i.e., ifcfg-eth1 must have +a device line of DEVICE=eth1. The setting of the MASTER= line will +also depend on the final bonding interface name chosen for your bond. +As with other network devices, these typically start at 0, and go up +one for each device, i.e., the first bonding instance is bond0, the +second is bond1, and so on. + + Next, create a bond network script. The file name for this +script will be /etc/sysconfig/network-scripts/ifcfg-bondX where X is +the number of the bond. For bond0 the file is named "ifcfg-bond0", +for bond1 it is named "ifcfg-bond1", and so on. Within that file, +place the following text: + +DEVICE=bond0 +IPADDR=192.168.1.1 +NETMASK=255.255.255.0 +NETWORK=192.168.1.0 +BROADCAST=192.168.1.255 +ONBOOT=yes +BOOTPROTO=none +USERCTL=no + + Be sure to change the networking specific lines (IPADDR, +NETMASK, NETWORK and BROADCAST) to match your network configuration. + + For later versions of initscripts, such as that found with Fedora +7 (or later) and Red Hat Enterprise Linux version 5 (or later), it is possible, +and, indeed, preferable, to specify the bonding options in the ifcfg-bond0 +file, e.g. a line of the format: + +BONDING_OPTS="mode=active-backup arp_interval=60 arp_ip_target=192.168.1.254" + + will configure the bond with the specified options. The options +specified in BONDING_OPTS are identical to the bonding module parameters +except for the arp_ip_target field when using versions of initscripts older +than and 8.57 (Fedora 8) and 8.45.19 (Red Hat Enterprise Linux 5.2). When +using older versions each target should be included as a separate option and +should be preceded by a '+' to indicate it should be added to the list of +queried targets, e.g., + + arp_ip_target=+192.168.1.1 arp_ip_target=+192.168.1.2 + + is the proper syntax to specify multiple targets. When specifying +options via BONDING_OPTS, it is not necessary to edit /etc/modprobe.d/*.conf. + + For even older versions of initscripts that do not support +BONDING_OPTS, it is necessary to edit /etc/modprobe.d/*.conf, depending upon +your distro) to load the bonding module with your desired options when the +bond0 interface is brought up. The following lines in /etc/modprobe.d/*.conf +will load the bonding module, and select its options: + +alias bond0 bonding +options bond0 mode=balance-alb miimon=100 + + Replace the sample parameters with the appropriate set of +options for your configuration. + + Finally run "/etc/rc.d/init.d/network restart" as root. This +will restart the networking subsystem and your bond link should be now +up and running. + +3.2.1 Using DHCP with Initscripts +--------------------------------- + + Recent versions of initscripts (the versions supplied with Fedora +Core 3 and Red Hat Enterprise Linux 4, or later versions, are reported to +work) have support for assigning IP information to bonding devices via +DHCP. + + To configure bonding for DHCP, configure it as described +above, except replace the line "BOOTPROTO=none" with "BOOTPROTO=dhcp" +and add a line consisting of "TYPE=Bonding". Note that the TYPE value +is case sensitive. + +3.2.2 Configuring Multiple Bonds with Initscripts +------------------------------------------------- + + Initscripts packages that are included with Fedora 7 and Red Hat +Enterprise Linux 5 support multiple bonding interfaces by simply +specifying the appropriate BONDING_OPTS= in ifcfg-bondX where X is the +number of the bond. This support requires sysfs support in the kernel, +and a bonding driver of version 3.0.0 or later. Other configurations may +not support this method for specifying multiple bonding interfaces; for +those instances, see the "Configuring Multiple Bonds Manually" section, +below. + +3.3 Configuring Bonding Manually with iproute2 +----------------------------------------------- + + This section applies to distros whose network initialization +scripts (the sysconfig or initscripts package) do not have specific +knowledge of bonding. One such distro is SuSE Linux Enterprise Server +version 8. + + The general method for these systems is to place the bonding +module parameters into a config file in /etc/modprobe.d/ (as +appropriate for the installed distro), then add modprobe and/or +`ip link` commands to the system's global init script. The name of +the global init script differs; for sysconfig, it is +/etc/init.d/boot.local and for initscripts it is /etc/rc.d/rc.local. + + For example, if you wanted to make a simple bond of two e100 +devices (presumed to be eth0 and eth1), and have it persist across +reboots, edit the appropriate file (/etc/init.d/boot.local or +/etc/rc.d/rc.local), and add the following: + +modprobe bonding mode=balance-alb miimon=100 +modprobe e100 +ifconfig bond0 192.168.1.1 netmask 255.255.255.0 up +ip link set eth0 master bond0 +ip link set eth1 master bond0 + + Replace the example bonding module parameters and bond0 +network configuration (IP address, netmask, etc) with the appropriate +values for your configuration. + + Unfortunately, this method will not provide support for the +ifup and ifdown scripts on the bond devices. To reload the bonding +configuration, it is necessary to run the initialization script, e.g., + +# /etc/init.d/boot.local + + or + +# /etc/rc.d/rc.local + + It may be desirable in such a case to create a separate script +which only initializes the bonding configuration, then call that +separate script from within boot.local. This allows for bonding to be +enabled without re-running the entire global init script. + + To shut down the bonding devices, it is necessary to first +mark the bonding device itself as being down, then remove the +appropriate device driver modules. For our example above, you can do +the following: + +# ifconfig bond0 down +# rmmod bonding +# rmmod e100 + + Again, for convenience, it may be desirable to create a script +with these commands. + + +3.3.1 Configuring Multiple Bonds Manually +----------------------------------------- + + This section contains information on configuring multiple +bonding devices with differing options for those systems whose network +initialization scripts lack support for configuring multiple bonds. + + If you require multiple bonding devices, but all with the same +options, you may wish to use the "max_bonds" module parameter, +documented above. + + To create multiple bonding devices with differing options, it is +preferable to use bonding parameters exported by sysfs, documented in the +section below. + + For versions of bonding without sysfs support, the only means to +provide multiple instances of bonding with differing options is to load +the bonding driver multiple times. Note that current versions of the +sysconfig network initialization scripts handle this automatically; if +your distro uses these scripts, no special action is needed. See the +section Configuring Bonding Devices, above, if you're not sure about your +network initialization scripts. + + To load multiple instances of the module, it is necessary to +specify a different name for each instance (the module loading system +requires that every loaded module, even multiple instances of the same +module, have a unique name). This is accomplished by supplying multiple +sets of bonding options in /etc/modprobe.d/*.conf, for example: + +alias bond0 bonding +options bond0 -o bond0 mode=balance-rr miimon=100 + +alias bond1 bonding +options bond1 -o bond1 mode=balance-alb miimon=50 + + will load the bonding module two times. The first instance is +named "bond0" and creates the bond0 device in balance-rr mode with an +miimon of 100. The second instance is named "bond1" and creates the +bond1 device in balance-alb mode with an miimon of 50. + + In some circumstances (typically with older distributions), +the above does not work, and the second bonding instance never sees +its options. In that case, the second options line can be substituted +as follows: + +install bond1 /sbin/modprobe --ignore-install bonding -o bond1 \ + mode=balance-alb miimon=50 + + This may be repeated any number of times, specifying a new and +unique name in place of bond1 for each subsequent instance. + + It has been observed that some Red Hat supplied kernels are unable +to rename modules at load time (the "-o bond1" part). Attempts to pass +that option to modprobe will produce an "Operation not permitted" error. +This has been reported on some Fedora Core kernels, and has been seen on +RHEL 4 as well. On kernels exhibiting this problem, it will be impossible +to configure multiple bonds with differing parameters (as they are older +kernels, and also lack sysfs support). + +3.4 Configuring Bonding Manually via Sysfs +------------------------------------------ + + Starting with version 3.0.0, Channel Bonding may be configured +via the sysfs interface. This interface allows dynamic configuration +of all bonds in the system without unloading the module. It also +allows for adding and removing bonds at runtime. Ifenslave is no +longer required, though it is still supported. + + Use of the sysfs interface allows you to use multiple bonds +with different configurations without having to reload the module. +It also allows you to use multiple, differently configured bonds when +bonding is compiled into the kernel. + + You must have the sysfs filesystem mounted to configure +bonding this way. The examples in this document assume that you +are using the standard mount point for sysfs, e.g. /sys. If your +sysfs filesystem is mounted elsewhere, you will need to adjust the +example paths accordingly. + +Creating and Destroying Bonds +----------------------------- +To add a new bond foo: +# echo +foo > /sys/class/net/bonding_masters + +To remove an existing bond bar: +# echo -bar > /sys/class/net/bonding_masters + +To show all existing bonds: +# cat /sys/class/net/bonding_masters + +NOTE: due to 4K size limitation of sysfs files, this list may be +truncated if you have more than a few hundred bonds. This is unlikely +to occur under normal operating conditions. + +Adding and Removing Slaves +-------------------------- + Interfaces may be enslaved to a bond using the file +/sys/class/net/<bond>/bonding/slaves. The semantics for this file +are the same as for the bonding_masters file. + +To enslave interface eth0 to bond bond0: +# ifconfig bond0 up +# echo +eth0 > /sys/class/net/bond0/bonding/slaves + +To free slave eth0 from bond bond0: +# echo -eth0 > /sys/class/net/bond0/bonding/slaves + + When an interface is enslaved to a bond, symlinks between the +two are created in the sysfs filesystem. In this case, you would get +/sys/class/net/bond0/slave_eth0 pointing to /sys/class/net/eth0, and +/sys/class/net/eth0/master pointing to /sys/class/net/bond0. + + This means that you can tell quickly whether or not an +interface is enslaved by looking for the master symlink. Thus: +# echo -eth0 > /sys/class/net/eth0/master/bonding/slaves +will free eth0 from whatever bond it is enslaved to, regardless of +the name of the bond interface. + +Changing a Bond's Configuration +------------------------------- + Each bond may be configured individually by manipulating the +files located in /sys/class/net/<bond name>/bonding + + The names of these files correspond directly with the command- +line parameters described elsewhere in this file, and, with the +exception of arp_ip_target, they accept the same values. To see the +current setting, simply cat the appropriate file. + + A few examples will be given here; for specific usage +guidelines for each parameter, see the appropriate section in this +document. + +To configure bond0 for balance-alb mode: +# ifconfig bond0 down +# echo 6 > /sys/class/net/bond0/bonding/mode + - or - +# echo balance-alb > /sys/class/net/bond0/bonding/mode + NOTE: The bond interface must be down before the mode can be +changed. + +To enable MII monitoring on bond0 with a 1 second interval: +# echo 1000 > /sys/class/net/bond0/bonding/miimon + NOTE: If ARP monitoring is enabled, it will disabled when MII +monitoring is enabled, and vice-versa. + +To add ARP targets: +# echo +192.168.0.100 > /sys/class/net/bond0/bonding/arp_ip_target +# echo +192.168.0.101 > /sys/class/net/bond0/bonding/arp_ip_target + NOTE: up to 16 target addresses may be specified. + +To remove an ARP target: +# echo -192.168.0.100 > /sys/class/net/bond0/bonding/arp_ip_target + +To configure the interval between learning packet transmits: +# echo 12 > /sys/class/net/bond0/bonding/lp_interval + NOTE: the lp_inteval is the number of seconds between instances where +the bonding driver sends learning packets to each slaves peer switch. The +default interval is 1 second. + +Example Configuration +--------------------- + We begin with the same example that is shown in section 3.3, +executed with sysfs, and without using ifenslave. + + To make a simple bond of two e100 devices (presumed to be eth0 +and eth1), and have it persist across reboots, edit the appropriate +file (/etc/init.d/boot.local or /etc/rc.d/rc.local), and add the +following: + +modprobe bonding +modprobe e100 +echo balance-alb > /sys/class/net/bond0/bonding/mode +ifconfig bond0 192.168.1.1 netmask 255.255.255.0 up +echo 100 > /sys/class/net/bond0/bonding/miimon +echo +eth0 > /sys/class/net/bond0/bonding/slaves +echo +eth1 > /sys/class/net/bond0/bonding/slaves + + To add a second bond, with two e1000 interfaces in +active-backup mode, using ARP monitoring, add the following lines to +your init script: + +modprobe e1000 +echo +bond1 > /sys/class/net/bonding_masters +echo active-backup > /sys/class/net/bond1/bonding/mode +ifconfig bond1 192.168.2.1 netmask 255.255.255.0 up +echo +192.168.2.100 /sys/class/net/bond1/bonding/arp_ip_target +echo 2000 > /sys/class/net/bond1/bonding/arp_interval +echo +eth2 > /sys/class/net/bond1/bonding/slaves +echo +eth3 > /sys/class/net/bond1/bonding/slaves + +3.5 Configuration with Interfaces Support +----------------------------------------- + + This section applies to distros which use /etc/network/interfaces file +to describe network interface configuration, most notably Debian and it's +derivatives. + + The ifup and ifdown commands on Debian don't support bonding out of +the box. The ifenslave-2.6 package should be installed to provide bonding +support. Once installed, this package will provide bond-* options to be used +into /etc/network/interfaces. + + Note that ifenslave-2.6 package will load the bonding module and use +the ifenslave command when appropriate. + +Example Configurations +---------------------- + +In /etc/network/interfaces, the following stanza will configure bond0, in +active-backup mode, with eth0 and eth1 as slaves. + +auto bond0 +iface bond0 inet dhcp + bond-slaves eth0 eth1 + bond-mode active-backup + bond-miimon 100 + bond-primary eth0 eth1 + +If the above configuration doesn't work, you might have a system using +upstart for system startup. This is most notably true for recent +Ubuntu versions. The following stanza in /etc/network/interfaces will +produce the same result on those systems. + +auto bond0 +iface bond0 inet dhcp + bond-slaves none + bond-mode active-backup + bond-miimon 100 + +auto eth0 +iface eth0 inet manual + bond-master bond0 + bond-primary eth0 eth1 + +auto eth1 +iface eth1 inet manual + bond-master bond0 + bond-primary eth0 eth1 + +For a full list of bond-* supported options in /etc/network/interfaces and some +more advanced examples tailored to you particular distros, see the files in +/usr/share/doc/ifenslave-2.6. + +3.6 Overriding Configuration for Special Cases +---------------------------------------------- + +When using the bonding driver, the physical port which transmits a frame is +typically selected by the bonding driver, and is not relevant to the user or +system administrator. The output port is simply selected using the policies of +the selected bonding mode. On occasion however, it is helpful to direct certain +classes of traffic to certain physical interfaces on output to implement +slightly more complex policies. For example, to reach a web server over a +bonded interface in which eth0 connects to a private network, while eth1 +connects via a public network, it may be desirous to bias the bond to send said +traffic over eth0 first, using eth1 only as a fall back, while all other traffic +can safely be sent over either interface. Such configurations may be achieved +using the traffic control utilities inherent in linux. + +By default the bonding driver is multiqueue aware and 16 queues are created +when the driver initializes (see Documentation/networking/multiqueue.txt +for details). If more or less queues are desired the module parameter +tx_queues can be used to change this value. There is no sysfs parameter +available as the allocation is done at module init time. + +The output of the file /proc/net/bonding/bondX has changed so the output Queue +ID is now printed for each slave: + +Bonding Mode: fault-tolerance (active-backup) +Primary Slave: None +Currently Active Slave: eth0 +MII Status: up +MII Polling Interval (ms): 0 +Up Delay (ms): 0 +Down Delay (ms): 0 + +Slave Interface: eth0 +MII Status: up +Link Failure Count: 0 +Permanent HW addr: 00:1a:a0:12:8f:cb +Slave queue ID: 0 + +Slave Interface: eth1 +MII Status: up +Link Failure Count: 0 +Permanent HW addr: 00:1a:a0:12:8f:cc +Slave queue ID: 2 + +The queue_id for a slave can be set using the command: + +# echo "eth1:2" > /sys/class/net/bond0/bonding/queue_id + +Any interface that needs a queue_id set should set it with multiple calls +like the one above until proper priorities are set for all interfaces. On +distributions that allow configuration via initscripts, multiple 'queue_id' +arguments can be added to BONDING_OPTS to set all needed slave queues. + +These queue id's can be used in conjunction with the tc utility to configure +a multiqueue qdisc and filters to bias certain traffic to transmit on certain +slave devices. For instance, say we wanted, in the above configuration to +force all traffic bound to 192.168.1.100 to use eth1 in the bond as its output +device. The following commands would accomplish this: + +# tc qdisc add dev bond0 handle 1 root multiq + +# tc filter add dev bond0 protocol ip parent 1: prio 1 u32 match ip dst \ + 192.168.1.100 action skbedit queue_mapping 2 + +These commands tell the kernel to attach a multiqueue queue discipline to the +bond0 interface and filter traffic enqueued to it, such that packets with a dst +ip of 192.168.1.100 have their output queue mapping value overwritten to 2. +This value is then passed into the driver, causing the normal output path +selection policy to be overridden, selecting instead qid 2, which maps to eth1. + +Note that qid values begin at 1. Qid 0 is reserved to initiate to the driver +that normal output policy selection should take place. One benefit to simply +leaving the qid for a slave to 0 is the multiqueue awareness in the bonding +driver that is now present. This awareness allows tc filters to be placed on +slave devices as well as bond devices and the bonding driver will simply act as +a pass-through for selecting output queues on the slave device rather than +output port selection. + +This feature first appeared in bonding driver version 3.7.0 and support for +output slave selection was limited to round-robin and active-backup modes. + +4 Querying Bonding Configuration +================================= + +4.1 Bonding Configuration +------------------------- + + Each bonding device has a read-only file residing in the +/proc/net/bonding directory. The file contents include information +about the bonding configuration, options and state of each slave. + + For example, the contents of /proc/net/bonding/bond0 after the +driver is loaded with parameters of mode=0 and miimon=1000 is +generally as follows: + + Ethernet Channel Bonding Driver: 2.6.1 (October 29, 2004) + Bonding Mode: load balancing (round-robin) + Currently Active Slave: eth0 + MII Status: up + MII Polling Interval (ms): 1000 + Up Delay (ms): 0 + Down Delay (ms): 0 + + Slave Interface: eth1 + MII Status: up + Link Failure Count: 1 + + Slave Interface: eth0 + MII Status: up + Link Failure Count: 1 + + The precise format and contents will change depending upon the +bonding configuration, state, and version of the bonding driver. + +4.2 Network configuration +------------------------- + + The network configuration can be inspected using the ifconfig +command. Bonding devices will have the MASTER flag set; Bonding slave +devices will have the SLAVE flag set. The ifconfig output does not +contain information on which slaves are associated with which masters. + + In the example below, the bond0 interface is the master +(MASTER) while eth0 and eth1 are slaves (SLAVE). Notice all slaves of +bond0 have the same MAC address (HWaddr) as bond0 for all modes except +TLB and ALB that require a unique MAC address for each slave. + +# /sbin/ifconfig +bond0 Link encap:Ethernet HWaddr 00:C0:F0:1F:37:B4 + inet addr:XXX.XXX.XXX.YYY Bcast:XXX.XXX.XXX.255 Mask:255.255.252.0 + UP BROADCAST RUNNING MASTER MULTICAST MTU:1500 Metric:1 + RX packets:7224794 errors:0 dropped:0 overruns:0 frame:0 + TX packets:3286647 errors:1 dropped:0 overruns:1 carrier:0 + collisions:0 txqueuelen:0 + +eth0 Link encap:Ethernet HWaddr 00:C0:F0:1F:37:B4 + UP BROADCAST RUNNING SLAVE MULTICAST MTU:1500 Metric:1 + RX packets:3573025 errors:0 dropped:0 overruns:0 frame:0 + TX packets:1643167 errors:1 dropped:0 overruns:1 carrier:0 + collisions:0 txqueuelen:100 + Interrupt:10 Base address:0x1080 + +eth1 Link encap:Ethernet HWaddr 00:C0:F0:1F:37:B4 + UP BROADCAST RUNNING SLAVE MULTICAST MTU:1500 Metric:1 + RX packets:3651769 errors:0 dropped:0 overruns:0 frame:0 + TX packets:1643480 errors:0 dropped:0 overruns:0 carrier:0 + collisions:0 txqueuelen:100 + Interrupt:9 Base address:0x1400 + +5. Switch Configuration +======================= + + For this section, "switch" refers to whatever system the +bonded devices are directly connected to (i.e., where the other end of +the cable plugs into). This may be an actual dedicated switch device, +or it may be another regular system (e.g., another computer running +Linux), + + The active-backup, balance-tlb and balance-alb modes do not +require any specific configuration of the switch. + + The 802.3ad mode requires that the switch have the appropriate +ports configured as an 802.3ad aggregation. The precise method used +to configure this varies from switch to switch, but, for example, a +Cisco 3550 series switch requires that the appropriate ports first be +grouped together in a single etherchannel instance, then that +etherchannel is set to mode "lacp" to enable 802.3ad (instead of +standard EtherChannel). + + The balance-rr, balance-xor and broadcast modes generally +require that the switch have the appropriate ports grouped together. +The nomenclature for such a group differs between switches, it may be +called an "etherchannel" (as in the Cisco example, above), a "trunk +group" or some other similar variation. For these modes, each switch +will also have its own configuration options for the switch's transmit +policy to the bond. Typical choices include XOR of either the MAC or +IP addresses. The transmit policy of the two peers does not need to +match. For these three modes, the bonding mode really selects a +transmit policy for an EtherChannel group; all three will interoperate +with another EtherChannel group. + + +6. 802.1q VLAN Support +====================== + + It is possible to configure VLAN devices over a bond interface +using the 8021q driver. However, only packets coming from the 8021q +driver and passing through bonding will be tagged by default. Self +generated packets, for example, bonding's learning packets or ARP +packets generated by either ALB mode or the ARP monitor mechanism, are +tagged internally by bonding itself. As a result, bonding must +"learn" the VLAN IDs configured above it, and use those IDs to tag +self generated packets. + + For reasons of simplicity, and to support the use of adapters +that can do VLAN hardware acceleration offloading, the bonding +interface declares itself as fully hardware offloading capable, it gets +the add_vid/kill_vid notifications to gather the necessary +information, and it propagates those actions to the slaves. In case +of mixed adapter types, hardware accelerated tagged packets that +should go through an adapter that is not offloading capable are +"un-accelerated" by the bonding driver so the VLAN tag sits in the +regular location. + + VLAN interfaces *must* be added on top of a bonding interface +only after enslaving at least one slave. The bonding interface has a +hardware address of 00:00:00:00:00:00 until the first slave is added. +If the VLAN interface is created prior to the first enslavement, it +would pick up the all-zeroes hardware address. Once the first slave +is attached to the bond, the bond device itself will pick up the +slave's hardware address, which is then available for the VLAN device. + + Also, be aware that a similar problem can occur if all slaves +are released from a bond that still has one or more VLAN interfaces on +top of it. When a new slave is added, the bonding interface will +obtain its hardware address from the first slave, which might not +match the hardware address of the VLAN interfaces (which was +ultimately copied from an earlier slave). + + There are two methods to insure that the VLAN device operates +with the correct hardware address if all slaves are removed from a +bond interface: + + 1. Remove all VLAN interfaces then recreate them + + 2. Set the bonding interface's hardware address so that it +matches the hardware address of the VLAN interfaces. + + Note that changing a VLAN interface's HW address would set the +underlying device -- i.e. the bonding interface -- to promiscuous +mode, which might not be what you want. + + +7. Link Monitoring +================== + + The bonding driver at present supports two schemes for +monitoring a slave device's link state: the ARP monitor and the MII +monitor. + + At the present time, due to implementation restrictions in the +bonding driver itself, it is not possible to enable both ARP and MII +monitoring simultaneously. + +7.1 ARP Monitor Operation +------------------------- + + The ARP monitor operates as its name suggests: it sends ARP +queries to one or more designated peer systems on the network, and +uses the response as an indication that the link is operating. This +gives some assurance that traffic is actually flowing to and from one +or more peers on the local network. + + The ARP monitor relies on the device driver itself to verify +that traffic is flowing. In particular, the driver must keep up to +date the last receive time, dev->last_rx, and transmit start time, +dev->trans_start. If these are not updated by the driver, then the +ARP monitor will immediately fail any slaves using that driver, and +those slaves will stay down. If networking monitoring (tcpdump, etc) +shows the ARP requests and replies on the network, then it may be that +your device driver is not updating last_rx and trans_start. + +7.2 Configuring Multiple ARP Targets +------------------------------------ + + While ARP monitoring can be done with just one target, it can +be useful in a High Availability setup to have several targets to +monitor. In the case of just one target, the target itself may go +down or have a problem making it unresponsive to ARP requests. Having +an additional target (or several) increases the reliability of the ARP +monitoring. + + Multiple ARP targets must be separated by commas as follows: + +# example options for ARP monitoring with three targets +alias bond0 bonding +options bond0 arp_interval=60 arp_ip_target=192.168.0.1,192.168.0.3,192.168.0.9 + + For just a single target the options would resemble: + +# example options for ARP monitoring with one target +alias bond0 bonding +options bond0 arp_interval=60 arp_ip_target=192.168.0.100 + + +7.3 MII Monitor Operation +------------------------- + + The MII monitor monitors only the carrier state of the local +network interface. It accomplishes this in one of three ways: by +depending upon the device driver to maintain its carrier state, by +querying the device's MII registers, or by making an ethtool query to +the device. + + If the use_carrier module parameter is 1 (the default value), +then the MII monitor will rely on the driver for carrier state +information (via the netif_carrier subsystem). As explained in the +use_carrier parameter information, above, if the MII monitor fails to +detect carrier loss on the device (e.g., when the cable is physically +disconnected), it may be that the driver does not support +netif_carrier. + + If use_carrier is 0, then the MII monitor will first query the +device's (via ioctl) MII registers and check the link state. If that +request fails (not just that it returns carrier down), then the MII +monitor will make an ethtool ETHOOL_GLINK request to attempt to obtain +the same information. If both methods fail (i.e., the driver either +does not support or had some error in processing both the MII register +and ethtool requests), then the MII monitor will assume the link is +up. + +8. Potential Sources of Trouble +=============================== + +8.1 Adventures in Routing +------------------------- + + When bonding is configured, it is important that the slave +devices not have routes that supersede routes of the master (or, +generally, not have routes at all). For example, suppose the bonding +device bond0 has two slaves, eth0 and eth1, and the routing table is +as follows: + +Kernel IP routing table +Destination Gateway Genmask Flags MSS Window irtt Iface +10.0.0.0 0.0.0.0 255.255.0.0 U 40 0 0 eth0 +10.0.0.0 0.0.0.0 255.255.0.0 U 40 0 0 eth1 +10.0.0.0 0.0.0.0 255.255.0.0 U 40 0 0 bond0 +127.0.0.0 0.0.0.0 255.0.0.0 U 40 0 0 lo + + This routing configuration will likely still update the +receive/transmit times in the driver (needed by the ARP monitor), but +may bypass the bonding driver (because outgoing traffic to, in this +case, another host on network 10 would use eth0 or eth1 before bond0). + + The ARP monitor (and ARP itself) may become confused by this +configuration, because ARP requests (generated by the ARP monitor) +will be sent on one interface (bond0), but the corresponding reply +will arrive on a different interface (eth0). This reply looks to ARP +as an unsolicited ARP reply (because ARP matches replies on an +interface basis), and is discarded. The MII monitor is not affected +by the state of the routing table. + + The solution here is simply to insure that slaves do not have +routes of their own, and if for some reason they must, those routes do +not supersede routes of their master. This should generally be the +case, but unusual configurations or errant manual or automatic static +route additions may cause trouble. + +8.2 Ethernet Device Renaming +---------------------------- + + On systems with network configuration scripts that do not +associate physical devices directly with network interface names (so +that the same physical device always has the same "ethX" name), it may +be necessary to add some special logic to config files in +/etc/modprobe.d/. + + For example, given a modules.conf containing the following: + +alias bond0 bonding +options bond0 mode=some-mode miimon=50 +alias eth0 tg3 +alias eth1 tg3 +alias eth2 e1000 +alias eth3 e1000 + + If neither eth0 and eth1 are slaves to bond0, then when the +bond0 interface comes up, the devices may end up reordered. This +happens because bonding is loaded first, then its slave device's +drivers are loaded next. Since no other drivers have been loaded, +when the e1000 driver loads, it will receive eth0 and eth1 for its +devices, but the bonding configuration tries to enslave eth2 and eth3 +(which may later be assigned to the tg3 devices). + + Adding the following: + +add above bonding e1000 tg3 + + causes modprobe to load e1000 then tg3, in that order, when +bonding is loaded. This command is fully documented in the +modules.conf manual page. + + On systems utilizing modprobe an equivalent problem can occur. +In this case, the following can be added to config files in +/etc/modprobe.d/ as: + +softdep bonding pre: tg3 e1000 + + This will load tg3 and e1000 modules before loading the bonding one. +Full documentation on this can be found in the modprobe.d and modprobe +manual pages. + +8.3. Painfully Slow Or No Failed Link Detection By Miimon +--------------------------------------------------------- + + By default, bonding enables the use_carrier option, which +instructs bonding to trust the driver to maintain carrier state. + + As discussed in the options section, above, some drivers do +not support the netif_carrier_on/_off link state tracking system. +With use_carrier enabled, bonding will always see these links as up, +regardless of their actual state. + + Additionally, other drivers do support netif_carrier, but do +not maintain it in real time, e.g., only polling the link state at +some fixed interval. In this case, miimon will detect failures, but +only after some long period of time has expired. If it appears that +miimon is very slow in detecting link failures, try specifying +use_carrier=0 to see if that improves the failure detection time. If +it does, then it may be that the driver checks the carrier state at a +fixed interval, but does not cache the MII register values (so the +use_carrier=0 method of querying the registers directly works). If +use_carrier=0 does not improve the failover, then the driver may cache +the registers, or the problem may be elsewhere. + + Also, remember that miimon only checks for the device's +carrier state. It has no way to determine the state of devices on or +beyond other ports of a switch, or if a switch is refusing to pass +traffic while still maintaining carrier on. + +9. SNMP agents +=============== + + If running SNMP agents, the bonding driver should be loaded +before any network drivers participating in a bond. This requirement +is due to the interface index (ipAdEntIfIndex) being associated to +the first interface found with a given IP address. That is, there is +only one ipAdEntIfIndex for each IP address. For example, if eth0 and +eth1 are slaves of bond0 and the driver for eth0 is loaded before the +bonding driver, the interface for the IP address will be associated +with the eth0 interface. This configuration is shown below, the IP +address 192.168.1.1 has an interface index of 2 which indexes to eth0 +in the ifDescr table (ifDescr.2). + + interfaces.ifTable.ifEntry.ifDescr.1 = lo + interfaces.ifTable.ifEntry.ifDescr.2 = eth0 + interfaces.ifTable.ifEntry.ifDescr.3 = eth1 + interfaces.ifTable.ifEntry.ifDescr.4 = eth2 + interfaces.ifTable.ifEntry.ifDescr.5 = eth3 + interfaces.ifTable.ifEntry.ifDescr.6 = bond0 + ip.ipAddrTable.ipAddrEntry.ipAdEntIfIndex.10.10.10.10 = 5 + ip.ipAddrTable.ipAddrEntry.ipAdEntIfIndex.192.168.1.1 = 2 + ip.ipAddrTable.ipAddrEntry.ipAdEntIfIndex.10.74.20.94 = 4 + ip.ipAddrTable.ipAddrEntry.ipAdEntIfIndex.127.0.0.1 = 1 + + This problem is avoided by loading the bonding driver before +any network drivers participating in a bond. Below is an example of +loading the bonding driver first, the IP address 192.168.1.1 is +correctly associated with ifDescr.2. + + interfaces.ifTable.ifEntry.ifDescr.1 = lo + interfaces.ifTable.ifEntry.ifDescr.2 = bond0 + interfaces.ifTable.ifEntry.ifDescr.3 = eth0 + interfaces.ifTable.ifEntry.ifDescr.4 = eth1 + interfaces.ifTable.ifEntry.ifDescr.5 = eth2 + interfaces.ifTable.ifEntry.ifDescr.6 = eth3 + ip.ipAddrTable.ipAddrEntry.ipAdEntIfIndex.10.10.10.10 = 6 + ip.ipAddrTable.ipAddrEntry.ipAdEntIfIndex.192.168.1.1 = 2 + ip.ipAddrTable.ipAddrEntry.ipAdEntIfIndex.10.74.20.94 = 5 + ip.ipAddrTable.ipAddrEntry.ipAdEntIfIndex.127.0.0.1 = 1 + + While some distributions may not report the interface name in +ifDescr, the association between the IP address and IfIndex remains +and SNMP functions such as Interface_Scan_Next will report that +association. + +10. Promiscuous mode +==================== + + When running network monitoring tools, e.g., tcpdump, it is +common to enable promiscuous mode on the device, so that all traffic +is seen (instead of seeing only traffic destined for the local host). +The bonding driver handles promiscuous mode changes to the bonding +master device (e.g., bond0), and propagates the setting to the slave +devices. + + For the balance-rr, balance-xor, broadcast, and 802.3ad modes, +the promiscuous mode setting is propagated to all slaves. + + For the active-backup, balance-tlb and balance-alb modes, the +promiscuous mode setting is propagated only to the active slave. + + For balance-tlb mode, the active slave is the slave currently +receiving inbound traffic. + + For balance-alb mode, the active slave is the slave used as a +"primary." This slave is used for mode-specific control traffic, for +sending to peers that are unassigned or if the load is unbalanced. + + For the active-backup, balance-tlb and balance-alb modes, when +the active slave changes (e.g., due to a link failure), the +promiscuous setting will be propagated to the new active slave. + +11. Configuring Bonding for High Availability +============================================= + + High Availability refers to configurations that provide +maximum network availability by having redundant or backup devices, +links or switches between the host and the rest of the world. The +goal is to provide the maximum availability of network connectivity +(i.e., the network always works), even though other configurations +could provide higher throughput. + +11.1 High Availability in a Single Switch Topology +-------------------------------------------------- + + If two hosts (or a host and a single switch) are directly +connected via multiple physical links, then there is no availability +penalty to optimizing for maximum bandwidth. In this case, there is +only one switch (or peer), so if it fails, there is no alternative +access to fail over to. Additionally, the bonding load balance modes +support link monitoring of their members, so if individual links fail, +the load will be rebalanced across the remaining devices. + + See Section 12, "Configuring Bonding for Maximum Throughput" +for information on configuring bonding with one peer device. + +11.2 High Availability in a Multiple Switch Topology +---------------------------------------------------- + + With multiple switches, the configuration of bonding and the +network changes dramatically. In multiple switch topologies, there is +a trade off between network availability and usable bandwidth. + + Below is a sample network, configured to maximize the +availability of the network: + + | | + |port3 port3| + +-----+----+ +-----+----+ + | |port2 ISL port2| | + | switch A +--------------------------+ switch B | + | | | | + +-----+----+ +-----++---+ + |port1 port1| + | +-------+ | + +-------------+ host1 +---------------+ + eth0 +-------+ eth1 + + In this configuration, there is a link between the two +switches (ISL, or inter switch link), and multiple ports connecting to +the outside world ("port3" on each switch). There is no technical +reason that this could not be extended to a third switch. + +11.2.1 HA Bonding Mode Selection for Multiple Switch Topology +------------------------------------------------------------- + + In a topology such as the example above, the active-backup and +broadcast modes are the only useful bonding modes when optimizing for +availability; the other modes require all links to terminate on the +same peer for them to behave rationally. + +active-backup: This is generally the preferred mode, particularly if + the switches have an ISL and play together well. If the + network configuration is such that one switch is specifically + a backup switch (e.g., has lower capacity, higher cost, etc), + then the primary option can be used to insure that the + preferred link is always used when it is available. + +broadcast: This mode is really a special purpose mode, and is suitable + only for very specific needs. For example, if the two + switches are not connected (no ISL), and the networks beyond + them are totally independent. In this case, if it is + necessary for some specific one-way traffic to reach both + independent networks, then the broadcast mode may be suitable. + +11.2.2 HA Link Monitoring Selection for Multiple Switch Topology +---------------------------------------------------------------- + + The choice of link monitoring ultimately depends upon your +switch. If the switch can reliably fail ports in response to other +failures, then either the MII or ARP monitors should work. For +example, in the above example, if the "port3" link fails at the remote +end, the MII monitor has no direct means to detect this. The ARP +monitor could be configured with a target at the remote end of port3, +thus detecting that failure without switch support. + + In general, however, in a multiple switch topology, the ARP +monitor can provide a higher level of reliability in detecting end to +end connectivity failures (which may be caused by the failure of any +individual component to pass traffic for any reason). Additionally, +the ARP monitor should be configured with multiple targets (at least +one for each switch in the network). This will insure that, +regardless of which switch is active, the ARP monitor has a suitable +target to query. + + Note, also, that of late many switches now support a functionality +generally referred to as "trunk failover." This is a feature of the +switch that causes the link state of a particular switch port to be set +down (or up) when the state of another switch port goes down (or up). +Its purpose is to propagate link failures from logically "exterior" ports +to the logically "interior" ports that bonding is able to monitor via +miimon. Availability and configuration for trunk failover varies by +switch, but this can be a viable alternative to the ARP monitor when using +suitable switches. + +12. Configuring Bonding for Maximum Throughput +============================================== + +12.1 Maximizing Throughput in a Single Switch Topology +------------------------------------------------------ + + In a single switch configuration, the best method to maximize +throughput depends upon the application and network environment. The +various load balancing modes each have strengths and weaknesses in +different environments, as detailed below. + + For this discussion, we will break down the topologies into +two categories. Depending upon the destination of most traffic, we +categorize them into either "gatewayed" or "local" configurations. + + In a gatewayed configuration, the "switch" is acting primarily +as a router, and the majority of traffic passes through this router to +other networks. An example would be the following: + + + +----------+ +----------+ + | |eth0 port1| | to other networks + | Host A +---------------------+ router +-------------------> + | +---------------------+ | Hosts B and C are out + | |eth1 port2| | here somewhere + +----------+ +----------+ + + The router may be a dedicated router device, or another host +acting as a gateway. For our discussion, the important point is that +the majority of traffic from Host A will pass through the router to +some other network before reaching its final destination. + + In a gatewayed network configuration, although Host A may +communicate with many other systems, all of its traffic will be sent +and received via one other peer on the local network, the router. + + Note that the case of two systems connected directly via +multiple physical links is, for purposes of configuring bonding, the +same as a gatewayed configuration. In that case, it happens that all +traffic is destined for the "gateway" itself, not some other network +beyond the gateway. + + In a local configuration, the "switch" is acting primarily as +a switch, and the majority of traffic passes through this switch to +reach other stations on the same network. An example would be the +following: + + +----------+ +----------+ +--------+ + | |eth0 port1| +-------+ Host B | + | Host A +------------+ switch |port3 +--------+ + | +------------+ | +--------+ + | |eth1 port2| +------------------+ Host C | + +----------+ +----------+port4 +--------+ + + + Again, the switch may be a dedicated switch device, or another +host acting as a gateway. For our discussion, the important point is +that the majority of traffic from Host A is destined for other hosts +on the same local network (Hosts B and C in the above example). + + In summary, in a gatewayed configuration, traffic to and from +the bonded device will be to the same MAC level peer on the network +(the gateway itself, i.e., the router), regardless of its final +destination. In a local configuration, traffic flows directly to and +from the final destinations, thus, each destination (Host B, Host C) +will be addressed directly by their individual MAC addresses. + + This distinction between a gatewayed and a local network +configuration is important because many of the load balancing modes +available use the MAC addresses of the local network source and +destination to make load balancing decisions. The behavior of each +mode is described below. + + +12.1.1 MT Bonding Mode Selection for Single Switch Topology +----------------------------------------------------------- + + This configuration is the easiest to set up and to understand, +although you will have to decide which bonding mode best suits your +needs. The trade offs for each mode are detailed below: + +balance-rr: This mode is the only mode that will permit a single + TCP/IP connection to stripe traffic across multiple + interfaces. It is therefore the only mode that will allow a + single TCP/IP stream to utilize more than one interface's + worth of throughput. This comes at a cost, however: the + striping generally results in peer systems receiving packets out + of order, causing TCP/IP's congestion control system to kick + in, often by retransmitting segments. + + It is possible to adjust TCP/IP's congestion limits by + altering the net.ipv4.tcp_reordering sysctl parameter. The + usual default value is 3. But keep in mind TCP stack is able + to automatically increase this when it detects reorders. + + Note that the fraction of packets that will be delivered out of + order is highly variable, and is unlikely to be zero. The level + of reordering depends upon a variety of factors, including the + networking interfaces, the switch, and the topology of the + configuration. Speaking in general terms, higher speed network + cards produce more reordering (due to factors such as packet + coalescing), and a "many to many" topology will reorder at a + higher rate than a "many slow to one fast" configuration. + + Many switches do not support any modes that stripe traffic + (instead choosing a port based upon IP or MAC level addresses); + for those devices, traffic for a particular connection flowing + through the switch to a balance-rr bond will not utilize greater + than one interface's worth of bandwidth. + + If you are utilizing protocols other than TCP/IP, UDP for + example, and your application can tolerate out of order + delivery, then this mode can allow for single stream datagram + performance that scales near linearly as interfaces are added + to the bond. + + This mode requires the switch to have the appropriate ports + configured for "etherchannel" or "trunking." + +active-backup: There is not much advantage in this network topology to + the active-backup mode, as the inactive backup devices are all + connected to the same peer as the primary. In this case, a + load balancing mode (with link monitoring) will provide the + same level of network availability, but with increased + available bandwidth. On the plus side, active-backup mode + does not require any configuration of the switch, so it may + have value if the hardware available does not support any of + the load balance modes. + +balance-xor: This mode will limit traffic such that packets destined + for specific peers will always be sent over the same + interface. Since the destination is determined by the MAC + addresses involved, this mode works best in a "local" network + configuration (as described above), with destinations all on + the same local network. This mode is likely to be suboptimal + if all your traffic is passed through a single router (i.e., a + "gatewayed" network configuration, as described above). + + As with balance-rr, the switch ports need to be configured for + "etherchannel" or "trunking." + +broadcast: Like active-backup, there is not much advantage to this + mode in this type of network topology. + +802.3ad: This mode can be a good choice for this type of network + topology. The 802.3ad mode is an IEEE standard, so all peers + that implement 802.3ad should interoperate well. The 802.3ad + protocol includes automatic configuration of the aggregates, + so minimal manual configuration of the switch is needed + (typically only to designate that some set of devices is + available for 802.3ad). The 802.3ad standard also mandates + that frames be delivered in order (within certain limits), so + in general single connections will not see misordering of + packets. The 802.3ad mode does have some drawbacks: the + standard mandates that all devices in the aggregate operate at + the same speed and duplex. Also, as with all bonding load + balance modes other than balance-rr, no single connection will + be able to utilize more than a single interface's worth of + bandwidth. + + Additionally, the linux bonding 802.3ad implementation + distributes traffic by peer (using an XOR of MAC addresses + and packet type ID), so in a "gatewayed" configuration, all + outgoing traffic will generally use the same device. Incoming + traffic may also end up on a single device, but that is + dependent upon the balancing policy of the peer's 8023.ad + implementation. In a "local" configuration, traffic will be + distributed across the devices in the bond. + + Finally, the 802.3ad mode mandates the use of the MII monitor, + therefore, the ARP monitor is not available in this mode. + +balance-tlb: The balance-tlb mode balances outgoing traffic by peer. + Since the balancing is done according to MAC address, in a + "gatewayed" configuration (as described above), this mode will + send all traffic across a single device. However, in a + "local" network configuration, this mode balances multiple + local network peers across devices in a vaguely intelligent + manner (not a simple XOR as in balance-xor or 802.3ad mode), + so that mathematically unlucky MAC addresses (i.e., ones that + XOR to the same value) will not all "bunch up" on a single + interface. + + Unlike 802.3ad, interfaces may be of differing speeds, and no + special switch configuration is required. On the down side, + in this mode all incoming traffic arrives over a single + interface, this mode requires certain ethtool support in the + network device driver of the slave interfaces, and the ARP + monitor is not available. + +balance-alb: This mode is everything that balance-tlb is, and more. + It has all of the features (and restrictions) of balance-tlb, + and will also balance incoming traffic from local network + peers (as described in the Bonding Module Options section, + above). + + The only additional down side to this mode is that the network + device driver must support changing the hardware address while + the device is open. + +12.1.2 MT Link Monitoring for Single Switch Topology +---------------------------------------------------- + + The choice of link monitoring may largely depend upon which +mode you choose to use. The more advanced load balancing modes do not +support the use of the ARP monitor, and are thus restricted to using +the MII monitor (which does not provide as high a level of end to end +assurance as the ARP monitor). + +12.2 Maximum Throughput in a Multiple Switch Topology +----------------------------------------------------- + + Multiple switches may be utilized to optimize for throughput +when they are configured in parallel as part of an isolated network +between two or more systems, for example: + + +-----------+ + | Host A | + +-+---+---+-+ + | | | + +--------+ | +---------+ + | | | + +------+---+ +-----+----+ +-----+----+ + | Switch A | | Switch B | | Switch C | + +------+---+ +-----+----+ +-----+----+ + | | | + +--------+ | +---------+ + | | | + +-+---+---+-+ + | Host B | + +-----------+ + + In this configuration, the switches are isolated from one +another. One reason to employ a topology such as this is for an +isolated network with many hosts (a cluster configured for high +performance, for example), using multiple smaller switches can be more +cost effective than a single larger switch, e.g., on a network with 24 +hosts, three 24 port switches can be significantly less expensive than +a single 72 port switch. + + If access beyond the network is required, an individual host +can be equipped with an additional network device connected to an +external network; this host then additionally acts as a gateway. + +12.2.1 MT Bonding Mode Selection for Multiple Switch Topology +------------------------------------------------------------- + + In actual practice, the bonding mode typically employed in +configurations of this type is balance-rr. Historically, in this +network configuration, the usual caveats about out of order packet +delivery are mitigated by the use of network adapters that do not do +any kind of packet coalescing (via the use of NAPI, or because the +device itself does not generate interrupts until some number of +packets has arrived). When employed in this fashion, the balance-rr +mode allows individual connections between two hosts to effectively +utilize greater than one interface's bandwidth. + +12.2.2 MT Link Monitoring for Multiple Switch Topology +------------------------------------------------------ + + Again, in actual practice, the MII monitor is most often used +in this configuration, as performance is given preference over +availability. The ARP monitor will function in this topology, but its +advantages over the MII monitor are mitigated by the volume of probes +needed as the number of systems involved grows (remember that each +host in the network is configured with bonding). + +13. Switch Behavior Issues +========================== + +13.1 Link Establishment and Failover Delays +------------------------------------------- + + Some switches exhibit undesirable behavior with regard to the +timing of link up and down reporting by the switch. + + First, when a link comes up, some switches may indicate that +the link is up (carrier available), but not pass traffic over the +interface for some period of time. This delay is typically due to +some type of autonegotiation or routing protocol, but may also occur +during switch initialization (e.g., during recovery after a switch +failure). If you find this to be a problem, specify an appropriate +value to the updelay bonding module option to delay the use of the +relevant interface(s). + + Second, some switches may "bounce" the link state one or more +times while a link is changing state. This occurs most commonly while +the switch is initializing. Again, an appropriate updelay value may +help. + + Note that when a bonding interface has no active links, the +driver will immediately reuse the first link that goes up, even if the +updelay parameter has been specified (the updelay is ignored in this +case). If there are slave interfaces waiting for the updelay timeout +to expire, the interface that first went into that state will be +immediately reused. This reduces down time of the network if the +value of updelay has been overestimated, and since this occurs only in +cases with no connectivity, there is no additional penalty for +ignoring the updelay. + + In addition to the concerns about switch timings, if your +switches take a long time to go into backup mode, it may be desirable +to not activate a backup interface immediately after a link goes down. +Failover may be delayed via the downdelay bonding module option. + +13.2 Duplicated Incoming Packets +-------------------------------- + + NOTE: Starting with version 3.0.2, the bonding driver has logic to +suppress duplicate packets, which should largely eliminate this problem. +The following description is kept for reference. + + It is not uncommon to observe a short burst of duplicated +traffic when the bonding device is first used, or after it has been +idle for some period of time. This is most easily observed by issuing +a "ping" to some other host on the network, and noticing that the +output from ping flags duplicates (typically one per slave). + + For example, on a bond in active-backup mode with five slaves +all connected to one switch, the output may appear as follows: + +# ping -n 10.0.4.2 +PING 10.0.4.2 (10.0.4.2) from 10.0.3.10 : 56(84) bytes of data. +64 bytes from 10.0.4.2: icmp_seq=1 ttl=64 time=13.7 ms +64 bytes from 10.0.4.2: icmp_seq=1 ttl=64 time=13.8 ms (DUP!) +64 bytes from 10.0.4.2: icmp_seq=1 ttl=64 time=13.8 ms (DUP!) +64 bytes from 10.0.4.2: icmp_seq=1 ttl=64 time=13.8 ms (DUP!) +64 bytes from 10.0.4.2: icmp_seq=1 ttl=64 time=13.8 ms (DUP!) +64 bytes from 10.0.4.2: icmp_seq=2 ttl=64 time=0.216 ms +64 bytes from 10.0.4.2: icmp_seq=3 ttl=64 time=0.267 ms +64 bytes from 10.0.4.2: icmp_seq=4 ttl=64 time=0.222 ms + + This is not due to an error in the bonding driver, rather, it +is a side effect of how many switches update their MAC forwarding +tables. Initially, the switch does not associate the MAC address in +the packet with a particular switch port, and so it may send the +traffic to all ports until its MAC forwarding table is updated. Since +the interfaces attached to the bond may occupy multiple ports on a +single switch, when the switch (temporarily) floods the traffic to all +ports, the bond device receives multiple copies of the same packet +(one per slave device). + + The duplicated packet behavior is switch dependent, some +switches exhibit this, and some do not. On switches that display this +behavior, it can be induced by clearing the MAC forwarding table (on +most Cisco switches, the privileged command "clear mac address-table +dynamic" will accomplish this). + +14. Hardware Specific Considerations +==================================== + + This section contains additional information for configuring +bonding on specific hardware platforms, or for interfacing bonding +with particular switches or other devices. + +14.1 IBM BladeCenter +-------------------- + + This applies to the JS20 and similar systems. + + On the JS20 blades, the bonding driver supports only +balance-rr, active-backup, balance-tlb and balance-alb modes. This is +largely due to the network topology inside the BladeCenter, detailed +below. + +JS20 network adapter information +-------------------------------- + + All JS20s come with two Broadcom Gigabit Ethernet ports +integrated on the planar (that's "motherboard" in IBM-speak). In the +BladeCenter chassis, the eth0 port of all JS20 blades is hard wired to +I/O Module #1; similarly, all eth1 ports are wired to I/O Module #2. +An add-on Broadcom daughter card can be installed on a JS20 to provide +two more Gigabit Ethernet ports. These ports, eth2 and eth3, are +wired to I/O Modules 3 and 4, respectively. + + Each I/O Module may contain either a switch or a passthrough +module (which allows ports to be directly connected to an external +switch). Some bonding modes require a specific BladeCenter internal +network topology in order to function; these are detailed below. + + Additional BladeCenter-specific networking information can be +found in two IBM Redbooks (www.ibm.com/redbooks): + +"IBM eServer BladeCenter Networking Options" +"IBM eServer BladeCenter Layer 2-7 Network Switching" + +BladeCenter networking configuration +------------------------------------ + + Because a BladeCenter can be configured in a very large number +of ways, this discussion will be confined to describing basic +configurations. + + Normally, Ethernet Switch Modules (ESMs) are used in I/O +modules 1 and 2. In this configuration, the eth0 and eth1 ports of a +JS20 will be connected to different internal switches (in the +respective I/O modules). + + A passthrough module (OPM or CPM, optical or copper, +passthrough module) connects the I/O module directly to an external +switch. By using PMs in I/O module #1 and #2, the eth0 and eth1 +interfaces of a JS20 can be redirected to the outside world and +connected to a common external switch. + + Depending upon the mix of ESMs and PMs, the network will +appear to bonding as either a single switch topology (all PMs) or as a +multiple switch topology (one or more ESMs, zero or more PMs). It is +also possible to connect ESMs together, resulting in a configuration +much like the example in "High Availability in a Multiple Switch +Topology," above. + +Requirements for specific modes +------------------------------- + + The balance-rr mode requires the use of passthrough modules +for devices in the bond, all connected to an common external switch. +That switch must be configured for "etherchannel" or "trunking" on the +appropriate ports, as is usual for balance-rr. + + The balance-alb and balance-tlb modes will function with +either switch modules or passthrough modules (or a mix). The only +specific requirement for these modes is that all network interfaces +must be able to reach all destinations for traffic sent over the +bonding device (i.e., the network must converge at some point outside +the BladeCenter). + + The active-backup mode has no additional requirements. + +Link monitoring issues +---------------------- + + When an Ethernet Switch Module is in place, only the ARP +monitor will reliably detect link loss to an external switch. This is +nothing unusual, but examination of the BladeCenter cabinet would +suggest that the "external" network ports are the ethernet ports for +the system, when it fact there is a switch between these "external" +ports and the devices on the JS20 system itself. The MII monitor is +only able to detect link failures between the ESM and the JS20 system. + + When a passthrough module is in place, the MII monitor does +detect failures to the "external" port, which is then directly +connected to the JS20 system. + +Other concerns +-------------- + + The Serial Over LAN (SoL) link is established over the primary +ethernet (eth0) only, therefore, any loss of link to eth0 will result +in losing your SoL connection. It will not fail over with other +network traffic, as the SoL system is beyond the control of the +bonding driver. + + It may be desirable to disable spanning tree on the switch +(either the internal Ethernet Switch Module, or an external switch) to +avoid fail-over delay issues when using bonding. + + +15. Frequently Asked Questions +============================== + +1. Is it SMP safe? + + Yes. The old 2.0.xx channel bonding patch was not SMP safe. +The new driver was designed to be SMP safe from the start. + +2. What type of cards will work with it? + + Any Ethernet type cards (you can even mix cards - a Intel +EtherExpress PRO/100 and a 3com 3c905b, for example). For most modes, +devices need not be of the same speed. + + Starting with version 3.2.1, bonding also supports Infiniband +slaves in active-backup mode. + +3. How many bonding devices can I have? + + There is no limit. + +4. How many slaves can a bonding device have? + + This is limited only by the number of network interfaces Linux +supports and/or the number of network cards you can place in your +system. + +5. What happens when a slave link dies? + + If link monitoring is enabled, then the failing device will be +disabled. The active-backup mode will fail over to a backup link, and +other modes will ignore the failed link. The link will continue to be +monitored, and should it recover, it will rejoin the bond (in whatever +manner is appropriate for the mode). See the sections on High +Availability and the documentation for each mode for additional +information. + + Link monitoring can be enabled via either the miimon or +arp_interval parameters (described in the module parameters section, +above). In general, miimon monitors the carrier state as sensed by +the underlying network device, and the arp monitor (arp_interval) +monitors connectivity to another host on the local network. + + If no link monitoring is configured, the bonding driver will +be unable to detect link failures, and will assume that all links are +always available. This will likely result in lost packets, and a +resulting degradation of performance. The precise performance loss +depends upon the bonding mode and network configuration. + +6. Can bonding be used for High Availability? + + Yes. See the section on High Availability for details. + +7. Which switches/systems does it work with? + + The full answer to this depends upon the desired mode. + + In the basic balance modes (balance-rr and balance-xor), it +works with any system that supports etherchannel (also called +trunking). Most managed switches currently available have such +support, and many unmanaged switches as well. + + The advanced balance modes (balance-tlb and balance-alb) do +not have special switch requirements, but do need device drivers that +support specific features (described in the appropriate section under +module parameters, above). + + In 802.3ad mode, it works with systems that support IEEE +802.3ad Dynamic Link Aggregation. Most managed and many unmanaged +switches currently available support 802.3ad. + + The active-backup mode should work with any Layer-II switch. + +8. Where does a bonding device get its MAC address from? + + When using slave devices that have fixed MAC addresses, or when +the fail_over_mac option is enabled, the bonding device's MAC address is +the MAC address of the active slave. + + For other configurations, if not explicitly configured (with +ifconfig or ip link), the MAC address of the bonding device is taken from +its first slave device. This MAC address is then passed to all following +slaves and remains persistent (even if the first slave is removed) until +the bonding device is brought down or reconfigured. + + If you wish to change the MAC address, you can set it with +ifconfig or ip link: + +# ifconfig bond0 hw ether 00:11:22:33:44:55 + +# ip link set bond0 address 66:77:88:99:aa:bb + + The MAC address can be also changed by bringing down/up the +device and then changing its slaves (or their order): + +# ifconfig bond0 down ; modprobe -r bonding +# ifconfig bond0 .... up +# ifenslave bond0 eth... + + This method will automatically take the address from the next +slave that is added. + + To restore your slaves' MAC addresses, you need to detach them +from the bond (`ifenslave -d bond0 eth0'). The bonding driver will +then restore the MAC addresses that the slaves had before they were +enslaved. + +16. Resources and Links +======================= + + The latest version of the bonding driver can be found in the latest +version of the linux kernel, found on http://kernel.org + + The latest version of this document can be found in the latest kernel +source (named Documentation/networking/bonding.txt). + + Discussions regarding the usage of the bonding driver take place on the +bonding-devel mailing list, hosted at sourceforge.net. If you have questions or +problems, post them to the list. The list address is: + +bonding-devel@lists.sourceforge.net + + The administrative interface (to subscribe or unsubscribe) can +be found at: + +https://lists.sourceforge.net/lists/listinfo/bonding-devel + + Discussions regarding the development of the bonding driver take place +on the main Linux network mailing list, hosted at vger.kernel.org. The list +address is: + +netdev@vger.kernel.org + + The administrative interface (to subscribe or unsubscribe) can +be found at: + +http://vger.kernel.org/vger-lists.html#netdev + +Donald Becker's Ethernet Drivers and diag programs may be found at : + - http://web.archive.org/web/*/http://www.scyld.com/network/ + +You will also find a lot of information regarding Ethernet, NWay, MII, +etc. at www.scyld.com. + +-- END -- |