Date: Sun, 11 May 2008 12:07:34 -0700 (PDT) From: Matthew Dillon <dillon@apollo.backplane.com> To: Bakul Shah <bakul@bitblocks.com> Cc: freebsd-current@freebsd.org, Julian Elischer <julian@elischer.org> Subject: Re: tcp over slow links broken? Message-ID: <200805111907.m4BJ7YE7005447@apollo.backplane.com> References: <20080511070708.A1AF05B4D@mail.bitblocks.com>
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:On Sat, 10 May 2008 23:33:56 PDT Julian Elischer <julian@elischer.org> wrote:
:> Bakul Shah wrote:
:...
:>
:> that is just plain wierd... B seems to have gone deaf.
:
:Yup! As if the wrong segment is being queued up.
Hmm. It looks like C has gone deaf, not B. B is retransmitting from
sequence 4744 which is the last sequence that C acked. C is then not
acking any further packets.
14:22:42.411144 IP B.55535 > C.ssh: . 7664:9124(1460) ack 2016 win 65535
14:22:42.411259 IP B.55535 > C.ssh: . 9124:10584(1460) ack 2016 win 65535
14:22:42.468350 IP C.ssh > B.55535: . ack 4744 win 65535
14:22:42.490556 IP C.ssh > B.55535: . ack 4744 win 65535
14:22:42.830171 IP B.55535 > C.ssh: . 4744:6204(1460) ack 2016 win 65535
14:22:43.470135 IP B.55535 > C.ssh: . 4744:6204(1460) ack 2016 win 65535
14:22:44.549944 IP B.55535 > C.ssh: . 4744:6204(1460) ack 2016 win 65535
14:22:46.509750 IP B.55535 > C.ssh: . 4744:6204(1460) ack 2016 win 65535
14:22:50.229210 IP B.55535 > C.ssh: . 4744:6204(1460) ack 2016 win 65535
This sounds like a packet filter state issue. My guess is that
PF running on B is getting confused. Either PF is getting confused,
or the packet is getting munged somehow to the point where PF refuses
to bridge it.
The A->C path (the one that is working) is going through PF's NAT rules.
The B->C path is probably going through a different set of PF rules.
I suggest capturing a trace on C to see if C is actually receiving
B's retransmissions.
-Matt
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