From 571370c1555d2aa697733479a50957aff024bbcb Mon Sep 17 00:00:00 2001 From: Lennart Poettering Date: Fri, 8 Jan 2016 02:46:59 +0100 Subject: resolved: when we get a packet failure from a server, don't downgrade UDP to TCP or vice versa Under the assumption that packet failures (i.e. FORMERR, SERVFAIL, NOTIMP) are caused by packet contents, not used transport, we shouldn't switch between UDP and TCP when we get them, but only downgrade the higher levels down to UDP. --- src/resolve/resolved-dns-server.c | 8 ++++++++ 1 file changed, 8 insertions(+) (limited to 'src/resolve/resolved-dns-server.c') diff --git a/src/resolve/resolved-dns-server.c b/src/resolve/resolved-dns-server.c index 0de6c8cec0..1600e7c292 100644 --- a/src/resolve/resolved-dns-server.c +++ b/src/resolve/resolved-dns-server.c @@ -277,6 +277,14 @@ void dns_server_packet_failed(DnsServer *s, DnsServerFeatureLevel level) { if (s->possible_feature_level != level) return; + /* Invoked whenever we get a FORMERR, SERVFAIL or NOTIMP rcode from a server. This is an immediate trigger for + * us to go one feature level down. Except when we are already at TCP or UDP level, in which case there's no + * point in changing, under the assumption that packet failures are caused by packet contents, not by used + * transport. */ + + if (s->possible_feature_level <= DNS_SERVER_FEATURE_LEVEL_UDP) + return; + s->n_failed_attempts = (unsigned) -1; } -- cgit v1.2.3-54-g00ecf