summaryrefslogtreecommitdiff
path: root/src/libsystemd-network
diff options
context:
space:
mode:
authorTom Gundersen <teg@jklm.no>2015-08-27 08:54:41 +0200
committerTom Gundersen <teg@jklm.no>2015-08-28 11:05:32 +0200
commit83cedf7ae28925e37931e7e92d22be9c936a1def (patch)
tree89c615165cb234dc42da2ffe8554ab62e6f3ad92 /src/libsystemd-network
parent9c92a077b667fe3947cc8a9caa197dea8b80b8e0 (diff)
sd-dhcp-server: improve predictability of leases
Rather than having all clients attempt to get the same leases (starting at the beginning of the pool), make each client star at a random offset into the pool determined by their client id. This greatly increases the chances of a given client receiving the same IP address even though both the client and server have lost any lease information (and distinct server instances handing out the same leases).
Diffstat (limited to 'src/libsystemd-network')
-rw-r--r--src/libsystemd-network/dhcp-server-internal.h1
-rw-r--r--src/libsystemd-network/sd-dhcp-server.c16
2 files changed, 13 insertions, 4 deletions
diff --git a/src/libsystemd-network/dhcp-server-internal.h b/src/libsystemd-network/dhcp-server-internal.h
index 6cc794c937..268210fc50 100644
--- a/src/libsystemd-network/dhcp-server-internal.h
+++ b/src/libsystemd-network/dhcp-server-internal.h
@@ -59,7 +59,6 @@ struct sd_dhcp_server {
be32_t netmask;
be32_t pool_start;
size_t pool_size;
- size_t next_offer;
char *timezone;
diff --git a/src/libsystemd-network/sd-dhcp-server.c b/src/libsystemd-network/sd-dhcp-server.c
index a46858258b..89b9a4c6be 100644
--- a/src/libsystemd-network/sd-dhcp-server.c
+++ b/src/libsystemd-network/sd-dhcp-server.c
@@ -669,6 +669,8 @@ static int get_pool_offset(sd_dhcp_server *server, be32_t requested_ip) {
return be32toh(requested_ip) - be32toh(server->pool_start);
}
+#define HASH_KEY SD_ID128_MAKE(0d,1d,fe,bd,f1,24,bd,b3,47,f1,dd,6e,73,21,93,30)
+
int dhcp_server_handle_message(sd_dhcp_server *server, DHCPMessage *message,
size_t length) {
_cleanup_dhcp_request_free_ DHCPRequest *req = NULL;
@@ -716,12 +718,20 @@ int dhcp_server_handle_message(sd_dhcp_server *server, DHCPMessage *message,
if (existing_lease)
address = existing_lease->address;
else {
+ size_t next_offer;
+
+ /* even with no persistence of leases, we try to offer the same client
+ the same IP address. we do this by using the hash of the client id
+ as the offset into the pool of leases when finding the next free one */
+
+ next_offer = client_id_hash_func(&req->client_id, HASH_KEY.bytes) % server->pool_size;
+
for (i = 0; i < server->pool_size; i++) {
- if (!server->bound_leases[server->next_offer]) {
- address = htobe32(be32toh(server->pool_start) + server->next_offer);
+ if (!server->bound_leases[next_offer]) {
+ address = htobe32(be32toh(server->pool_start) + next_offer);
break;
} else
- server->next_offer = (server->next_offer + 1) % server->pool_size;
+ next_offer = (next_offer + 1) % server->pool_size;
}
}