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This patch fixes the out of sync scenarios while in SYN_RECV state. Quoting Jozsef, what it happens if we are out of sync if the following: > > b. conntrack entry is outdated, new SYN received > > - (b1) we ignore it but save the initialization data from it > > - (b2) when the reply SYN/ACK receives and it matches the saved data, > > we pick up the new connection This is what it should happen if we are in SYN_RECV state. Initially, the SYN packet hits b1, thus we save data from it. But the SYN/ACK packet is considered a retransmission given that we're in SYN_RECV state. Therefore, we never hit b2 and we don't get in sync. To fix this, we ignore SYN/ACK if we are in SYN_RECV. If the previous packet was a SYN, then we enter the ignore case that get us in sync. This patch helps a lot to conntrackd in stress scenarios (assumming a client that generates lots of small TCP connections). During the failover, consider that the new primary has injected one outdated flow in SYN_RECV state (this is likely to happen if the conntrack event rate is high because the backup will be a bit delayed from the primary). With the current code, if the client starts a new fresh connection that matches the tuple, the SYN packet will be ignored without updating the state tracking, and the SYN+ACK in reply will blocked as it will not pass checkings III or IV (since all state tracking in the original direction is not initialized because of the SYN packet was ignored and the ignore case that get us in sync is not applied). I posted a couple of patches before this one. Changli Gao spotted a simpler way to fix this problem. This patch implements his idea. Cc: Changli Gao <xiaosuo@gmail.com> Cc: Jozsef Kadlecsik <kadlec@blackhole.kfki.hu> Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org> Signed-off-by: Jozsef Kadlecsik <kadlec@blackhole.kfki.hu> Signed-off-by: Patrick McHardy <kaber@trash.net> |
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| xfrm | ||
| compat.c | ||
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| Makefile | ||
| nonet.c | ||
| socket.c | ||
| sysctl_net.c | ||
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