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More: TCP problem on 3.6 (was: SSH problem on 3.6)

To: misc_(_at_)_openbsd_(_dot_)_org
Subject: More: TCP problem on 3.6 (was: SSH problem on 3.6)
From: "Ilya A. Kovalenko" <shadow_(_at_)_oganer_(_dot_)_net>
Date: Fri, 12 Nov 2004 03:18:59 +0700
Organization: JSC Oganer-Service
Reply-to: "Ilya A. Kovalenko" <shadow_(_at_)_oganer_(_dot_)_net>
  Story short retell and additions:

  I face w/permanent TCP-delaying effect, on OpenBSD 3.6 (unlike
3.5- in same conditions).

  This effect shows it's worth only then I trying to work from home via
UTP fast-ethernet campus network (3 OpenBSD gateways, switches, cables):

             _____     ______      ________
  office    |     |   |      |    (        )
   _________|spoon|___|route0|____( campus  )
   __|__    |_____|   |______|   ( network )
  |     |   office     campus     (_______)
  | owl |     GW         GW           |
  |_____|                          ___|___
                             home |  NAT  |
                              GW  | void  |
                                  |_______|
                             ______   |
                            |      |__|
                            |buggy |  |
                            |______|  |

(working from "buggy" or "void" with "owl")

  This is, probably, the problem caused by campus network, but I
want to understand two things:
   >> what can be wrong with it (and how can I do work it around)
   >> why 3.5 can work via it, but not 3.6

"delayng effect" = infinite repetition of:
   >> receiving ~50 Kb (couple of seconds)
   >> delay 2-5 minutes
on high connection payload.
   

  Worked out suggestions:
   1. Tested on different 3.6 host (i.e. not HW-related)
   2. MTU=576, looking for non-standard MTU on middle
      gateways, trying to sniff fragmented packets
      (case of http://www.snailbook.com/faq/mtu-mismatch.auto.html)
   3. Compare sysctl variables 3.5 vs 3.6
   4. Disable MTU discovery (net.inet.ip.mtudisc=0)

  No, yet, valid how-to-repeat scenario.

  I captured connection fragment (receive before delay)
on source host(owl) and before destination (on void). Here is diff:

192.168.114.230 = owl, 172.30.3.64 = void

 192.168.114.230.62165 > 172.30.3.64.53661: . 86343492:86344004(512) ack 1478856698 win 16384
 172.30.3.64.53661 > 192.168.114.230.62165: . ack 512 win 65023 (DF)
 192.168.114.230.62165 > 172.30.3.64.53661: . 512:1024(512) ack 1 win 16384
 192.168.114.230.62165 > 172.30.3.64.53661: . 1024:1536(512) ack 1 win 16384
 172.30.3.64.53661 > 192.168.114.230.62165: . ack 1536 win 65535 (DF)
 192.168.114.230.62165 > 172.30.3.64.53661: . 1536:2048(512) ack 1 win 16384
 192.168.114.230.62165 > 172.30.3.64.53661: . 2048:2560(512) ack 1 win 16384
 192.168.114.230.62165 > 172.30.3.64.53661: . 2560:3072(512) ack 1 win 16384
 172.30.3.64.53661 > 192.168.114.230.62165: . ack 2560 win 64511 (DF)
 192.168.114.230.62165 > 172.30.3.64.53661: . 3072:3584(512) ack 1 win 16384
 192.168.114.230.62165 > 172.30.3.64.53661: . 3584:4096(512) ack 1 win 16384
 192.168.114.230.62165 > 172.30.3.64.53661: . 4096:4266(170) ack 1 win 16384
{... skipped ...}
 192.168.114.230.62165 > 172.30.3.64.53661: . 64976:65488(512) ack 1 win 16384
 192.168.114.230.62165 > 172.30.3.64.53661: . 65488:66000(512) ack 1 win 16384
 172.30.3.64.53661 > 192.168.114.230.62165: . ack 61392 win 43007 (DF)
 192.168.114.230.62165 > 172.30.3.64.53661: . 66000:66512(512) ack 1 win 16384
 192.168.114.230.62165 > 172.30.3.64.53661: . 66512:67024(512) ack 1 win 16384
 172.30.3.64.53661 > 192.168.114.230.62165: . ack 62416 win 41983 (DF)
 172.30.3.64.53661 > 192.168.114.230.62165: . ack 63440 win 40959 (DF)
 192.168.114.230.62165 > 172.30.3.64.53661: . 67024:67536(512) ack 1 win 16384
-192.168.114.230.62165 > 172.30.3.64.53661: . 67536:68048(512) ack 1 win 16384
-192.168.114.230.62165 > 172.30.3.64.53661: . 68048:68560(512) ack 1 win 16384
-192.168.114.230.62165 > 172.30.3.64.53661: . 68560:69072(512) ack 1 win 16384
 172.30.3.64.53661 > 192.168.114.230.62165: . ack 64464 win 39935 (DF)
-192.168.114.230.62165 > 172.30.3.64.53661: . 69072:69584(512) ack 1 win 16384
-192.168.114.230.62165 > 172.30.3.64.53661: . 69584:70096(512) ack 1 win 16384
 172.30.3.64.53661 > 192.168.114.230.62165: . ack 65488 win 38911 (DF)
-192.168.114.230.62165 > 172.30.3.64.53661: . 70096:70608(512) ack 1 win 16384
-192.168.114.230.62165 > 172.30.3.64.53661: . 70608:71120(512) ack 1 win 16384
 172.30.3.64.53661 > 192.168.114.230.62165: . ack 66512 win 37887 (DF)
-192.168.114.230.62165 > 172.30.3.64.53661: . 71120:71632(512) ack 1 win 16384
-192.168.114.230.62165 > 172.30.3.64.53661: . 71632:72144(512) ack 1 win 16384
 172.30.3.64.53661 > 192.168.114.230.62165: . ack 67536 win 36863 (DF)
-192.168.114.230.62165 > 172.30.3.64.53661: . 72144:72656(512) ack 1 win 16384
-192.168.114.230.62165 > 172.30.3.64.53661: . 72656:73168(512) ack 1 win 16384
 172.30.3.64.53661 > 192.168.114.230.62165: . ack 67536 win 40599 (DF)
 172.30.3.64.53661 > 192.168.114.230.62165: . ack 67536 win 65535 (DF)
-192.168.114.230.62165 > 172.30.3.64.53661: . 67536:68048(512) ack 1 win 16384
-192.168.114.230.62165 > 172.30.3.64.53661: . 67536:68048(512) ack 1 win 16384
-192.168.114.230.62165 > 172.30.3.64.53661: . 67536:68048(512) ack 1 win 16384
{... delay ...}

("-" - packets transmitted by "owl", but not received by "void")

  I.e. connection delayed as result of mass packet lost.

  Verbose listing (another session, another host):

received packets:

18:32:06.640897 192.168.114.219.54622 > 172.30.3.64.59618: . \
414682903:414684363(1460) ack 3724177995 win 17520 (ttl 64,  \
id 64464)
  4500 05dc fbd0 0000 4006 9669 c0a8 72db
  ac1e 0340 d55e e8e2 18b7 8f17 ddfa 724b
  5010 4470 c9f5 0000 0fb6 4605 5053 8d47
  1489 85ec fbff ff50 685e 9058 d0e8 a697
  d7ff 83c4 248b 85f4 fbff ff50 e833 19ff
  ff89
18:32:06.781453 172.30.3.64.59618 > 192.168.114.219.54622: . \
[tcp sum ok] 1:1(0) ack 1460 win 65535 (DF) (ttl 122, id 23403)
  4500 0028 5b6b 4000 7a06 c282 ac1e 0340
  c0a8 72db e8e2 d55e ddfa 724b 18b7 94cb
  5010 ffff 10e8 0000 0000 0000 0000
18:32:06.781726 192.168.114.219.54622 > 172.30.3.64.59618: . \
1460:2920(1460) ack 1 win 17520 (ttl 64, id 41424)
  4500 05dc a1d0 0000 4006 f069 c0a8 72db
  ac1e 0340 d55e e8e2 18b7 94cb ddfa 724b
  5010 4470 2cab 0000 26bf 0500 0000 83c4
  f4ff 7640 e8f7 0eff ffc7 4640 0000 0000
  c686 9400 0000 0083 c410 e9f4 0000 0083
  c4f4
18:32:06.782801 192.168.114.219.54622 > 172.30.3.64.59618: . \
2920:4380(1460) ack 1 win 17520 (ttl 64, id 44412)
  4500 05dc ad7c 0000 4006 e4bd c0a8 72db
  ac1e 0340 d55e e8e2 18b7 9a7f ddfa 724b
  5010 4470 a8a3 0000 83c4 fc53 8d5e 1453
  681a 9258 d0e8 468c d7ff 83c4 100f b646
  5889 9df0 fbff ff83 f802 7410 7f07 83f8
  0174

lost packets:

18:32:06.923974 192.168.114.219.54622 > 172.30.3.64.59618: . \
76156:77616(1460) ack 1 win 17520 (ttl 64, id 63422)
  4500 05dc f7be 0000 4006 9a7b c0a8 72db
  ac1e 0340 d55e e8e2 18b8 b893 ddfa 724b
  5010 4470 cd48 0000 5dd0 7414 83c4 f88b
  45fc 5068 2619 59d0 e873 17d6 ff8d 7600
  8da5 d8fb ffff 5b5e 5fc9 c390 5589 e583
  ec10
18:32:08.930202 192.168.114.219.54622 > 172.30.3.64.59618: . \
67396:68856(1460) ack 1 win 17520 (ttl 64, id 52825)
  4500 05dc ce59 0000 4006 c3e0 c0a8 72db
  ac1e 0340 d55e e8e2 18b8 965b ddfa 724b
  5010 4470 cc09 0000 5de8 c9c3 5589 e583
  ec10 5653 8b75 088b 4d10 8b41 0889 c3c1
  eb08 83e3 0489 daf6 c410 740d 83cb 18f6
  c420
18:32:12.930208 192.168.114.219.54622 > 172.30.3.64.59618: . \
67396:68856(1460) ack 1 win 17520 (ttl 64, id 53898)
  4500 05dc d28a 0000 4006 bfaf c0a8 72db
  ac1e 0340 d55e e8e2 18b8 965b ddfa 724b
  5010 4470 cc09 0000 5de8 c9c3 5589 e583
  ec10 5653 8b75 088b 4d10 8b41 0889 c3c1
  eb08 83e3 0489 daf6 c410 740d 83cb 18f6
  c420

  Any other ideas ? Need more debug info ?

Thank you

Ilya A. Kovalenko
S.A.
JSC Oganer-Service
References:
- SSH problems on 3.6
  - From: Ilya A. Kovalenko
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