TCP connection stalls on LAN

[Stephen Clark]

Jeremie Le Hen wrote:

>Hi,
>
>I'm running a quite recent -CURRENT.
>
>I don't understand what's happening.  According to tcpdump(1) it seems
>the two peers both keep acknowledging the same segment for ever.
>(See the file attached.)
>
>The peer is a Linksys router that have worked correctly for a while.
>The problem arises only with it, I can successfully connect to a
>NetBSD and a Windows host.
>
>I've attached the dump output.  Feel free to ask me for more infos.
>
>Note that automatic TCP socket buffer sizing is disabled (the same
>happens when enabled).  I've also disabled rxcsum and txcsum on
>my network adapter to narrow the possible sources of the problem.
>
>Regards,
>  
>
>------------------------------------------------------------------------
>
>09:14:57.593729 IP (tos 0x0, ttl  64, id 27791, offset 0, flags [DF], proto: TCP (6), length: 64) 192.168.1.3.56556 > 192.168.1.1.80: S, cksum 0xe59c (correct), 487760288:487760288(0) win 65535 <mss 1460,nop,wscale 8,nop,nop,timestamp 54669015 0,sackOK,eol>
>09:14:57.597224 IP (tos 0x0, ttl  64, id 0, offset 0, flags [DF], proto: TCP (6), length: 60) 192.168.1.1.80 > 192.168.1.3.56556: S, cksum 0xe603 (correct), 2303804549:2303804549(0) ack 487760289 win 5792 <mss 1460,sackOK,timestamp 76829 54669015,nop,wscale 0>
>09:14:57.597306 IP (tos 0x0, ttl  64, id 2460, offset 0, flags [DF], proto: TCP (6), length: 52) 192.168.1.3.56556 > 192.168.1.1.80: ., cksum 0x2a62 (correct), 1:1(0) ack 1 win 260 <nop,nop,timestamp 54669018 76829>
>09:14:57.601590 IP (tos 0x0, ttl  64, id 48542, offset 0, flags [DF], proto: TCP (6), length: 488) 192.168.1.3.56556 > 192.168.1.1.80: P 1:437(436) ack 1 win 260 <nop,nop,timestamp 54669023 76829>
>09:14:57.602390 IP (tos 0x0, ttl  64, id 26779, offset 0, flags [DF], proto: TCP (6), length: 52) 192.168.1.1.80 > 192.168.1.3.56556: ., cksum 0x108d (correct), 1:1(0) ack 437 win 6432 <nop,nop,timestamp 76829 54669023>
>09:14:57.605968 IP (tos 0x0, ttl  64, id 26780, offset 0, flags [DF], proto: TCP (6), length: 308) 192.168.1.1.80 > 192.168.1.3.56556: P 1:257(256) ack 437 win 6432 <nop,nop,timestamp 76829 54669023>
>09:14:57.613414 IP (tos 0x0, ttl  64, id 26781, offset 0, flags [DF], proto: TCP (6), length: 1500) 192.168.1.1.80 > 192.168.1.3.56556: . 257:1705(1448) ack 437 win 6432 <nop,nop,timestamp 76830 54669023>
>09:14:57.613465 IP (tos 0x0, ttl  64, id 38624, offset 0, flags [DF], proto: TCP (6), length: 52) 192.168.1.3.56556 > 192.168.1.1.80: ., cksum 0x21fb (correct), 437:437(0) ack 1705 win 254 <nop,nop,timestamp 54669035 76829>
>09:14:57.816442 IP (tos 0x0, ttl  64, id 26782, offset 0, flags [DF], proto: TCP (6), length: 52) 192.168.1.1.80 > 192.168.1.3.56556: ., cksum 0x09c4 (correct), 1704:1704(0) ack 437 win 6432 <nop,nop,timestamp 76851 54669035>
>09:14:57.816489 IP (tos 0x0, ttl  64, id 4315, offset 0, flags [DF], proto: TCP (6), length: 52) 192.168.1.3.56556 > 192.168.1.1.80: ., cksum 0x212a (correct), 437:437(0) ack 1705 win 260 <nop,nop,timestamp 54669238 76829>
>09:14:58.236395 IP (tos 0x0, ttl  64, id 26783, offset 0, flags [DF], proto: TCP (6), length: 52) 192.168.1.1.80 > 192.168.1.3.56556: ., cksum 0x08cf (correct), 1704:1704(0) ack 437 win 6432 <nop,nop,timestamp 76893 54669238>
>09:14:58.236448 IP (tos 0x0, ttl  64, id 48004, offset 0, flags [DF], proto: TCP (6), length: 52) 192.168.1.3.56556 > 192.168.1.1.80: ., cksum 0x1f86 (correct), 437:437(0) ack 1705 win 260 <nop,nop,timestamp 54669658 76829>
>09:14:59.076354 IP (tos 0x0, ttl  64, id 26784, offset 0, flags [DF], proto: TCP (6), length: 52) 192.168.1.1.80 > 192.168.1.3.56556: ., cksum 0x06d7 (correct), 1704:1704(0) ack 437 win 6432 <nop,nop,timestamp 76977 54669658>
>09:14:59.076403 IP (tos 0x0, ttl  64, id 4302, offset 0, flags [DF], proto: TCP (6), length: 52) 192.168.1.3.56556 > 192.168.1.1.80: ., cksum 0x1c3e (correct), 437:437(0) ack 1705 win 260 <nop,nop,timestamp 54670498 76829>
>09:15:00.756298 IP (tos 0x0, ttl  64, id 26785, offset 0, flags [DF], proto: TCP (6), length: 52) 192.168.1.1.80 > 192.168.1.3.56556: ., cksum 0x02e7 (correct), 1704:1704(0) ack 437 win 6432 <nop,nop,timestamp 77145 54670498>
>09:15:00.756344 IP (tos 0x0, ttl  64, id 47006, offset 0, flags [DF], proto: TCP (6), length: 52) 192.168.1.3.56556 > 192.168.1.1.80: ., cksum 0x15ae (correct), 437:437(0) ack 1705 win 260 <nop,nop,timestamp 54672178 76829>
>09:15:04.116021 IP (tos 0x0, ttl  64, id 26786, offset 0, flags [DF], proto: TCP (6), length: 52) 192.168.1.1.80 > 192.168.1.3.56556: ., cksum 0xfb06 (correct), 1704:1704(0) ack 437 win 6432 <nop,nop,timestamp 77481 54672178>
>09:15:04.116068 IP (tos 0x0, ttl  64, id 63692, offset 0, flags [DF], proto: TCP (6), length: 52) 192.168.1.3.56556 > 192.168.1.1.80: ., cksum 0x088e (correct), 437:437(0) ack 1705 win 260 <nop,nop,timestamp 54675538 76829>
>  
>
>  
>
looks like the 1500 byte packet is not making it thru the network. Lower 
your mtu and see if this
helps.

Steve


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