tech-net: IP NAT problem over pppoe(4)

Subject: IP NAT problem over pppoe(4)
To: None <tech-net@netbsd.org>
From: Matthias Scheler <tron@zhadum.de>
List: tech-net
Date: 12/10/2002 11:37:23
	Hello,

after changing the Internet provider for my DSL line I experience
strange connectivity problems on TCP connections of a NetBSD system
behind my NetBSD IP NAT gateway.

The affected IP NAT client can download and upload files via "scp"
from and to other systems on the Internet without problems. The
trouble starts if I try to access "cvs.netbsd.org":

a) The IP NAT gateway can upload files to and download files from
   "cvs.netbsd.org" via "scp" without problems.
b) The IP NAT client can upload files to "cvs.netbsd.org" with "scp"
   but always gets stuck while downloading files.

Here is a trace of such a stuck connection:

PPPoE interface of the IP NAT gateway:
10:55:16.498714 PPPoE  [ses 0xfee] colwyn.zhadum.de.16389 > netbsd.hut.fi.ssh: S 565709589:565709589(0) win 16384 <mss 1412,nop,wscale 0,nop,nop,timestamp 0 0> (DF)
10:55:16.615547 PPPoE  [ses 0xfee] netbsd.hut.fi.ssh > colwyn.zhadum.de.16389: S 2400819126:2400819126(0) ack 565709590 win 32768 <mss 1460,nop,wscale 0,nop,nop,timestamp 2574486 0>
10:55:16.615845 PPPoE  [ses 0xfee] colwyn.zhadum.de.16389 > netbsd.hut.fi.ssh: . ack 1 win 17520 <nop,nop,timestamp 1 2574486> (DF)
10:55:16.731603 PPPoE  [ses 0xfee] netbsd.hut.fi.ssh > colwyn.zhadum.de.16389: P 1:53(52) ack 1 win 33580 <nop,nop,timestamp 2574487 0>
10:55:16.732073 PPPoE  [ses 0xfee] colwyn.zhadum.de.16389 > netbsd.hut.fi.ssh: P 1:50(49) ack 53 win 17520 <nop,nop,timestamp 1 2574487> (DF)
10:55:16.854997 PPPoE  [ses 0xfee] netbsd.hut.fi.ssh > colwyn.zhadum.de.16389: P 53:693(640) ack 50 win 33580 <nop,nop,timestamp 2574487 1>
10:55:16.855447 PPPoE  [ses 0xfee] colwyn.zhadum.de.16389 > netbsd.hut.fi.ssh: P 50:594(544) ack 693 win 16880 <nop,nop,timestamp 1 2574487> (DF)
10:55:17.113545 PPPoE  [ses 0xfee] netbsd.hut.fi.ssh > colwyn.zhadum.de.16389: . ack 594 win 33580 <nop,nop,timestamp 2574487 1>
10:55:17.113840 PPPoE  [ses 0xfee] colwyn.zhadum.de.16389 > netbsd.hut.fi.ssh: P 594:618(24) ack 693 win 17520 <nop,nop,timestamp 2 2574487> (DF)
10:55:17.294757 PPPoE  [ses 0xfee] netbsd.hut.fi.ssh > colwyn.zhadum.de.16389: P 693:1117(424) ack 618 win 33580 <nop,nop,timestamp 2574488 2>
10:55:17.327662 PPPoE  [ses 0xfee] colwyn.zhadum.de.16389 > netbsd.hut.fi.ssh: P 618:1034(416) ack 1117 win 17520 <nop,nop,timestamp 2 2574488> (DF)
10:55:17.513284 PPPoE  [ses 0xfee] netbsd.hut.fi.ssh > colwyn.zhadum.de.16389: . ack 1034 win 33164 <nop,nop,timestamp 2574488 2>
10:55:19.284032 PPPoE  [ses 0xfee] netbsd.hut.fi.ssh > colwyn.zhadum.de.16389: P 1117:1853(736) ack 1034 win 33580 <nop,nop,timestamp 2574492 2>
10:55:19.343598 PPPoE  [ses 0xfee] colwyn.zhadum.de.16389 > netbsd.hut.fi.ssh: P 1034:1050(16) ack 1853 win 17520 <nop,nop,timestamp 6 2574492> (DF)
10:55:19.512480 PPPoE  [ses 0xfee] netbsd.hut.fi.ssh > colwyn.zhadum.de.16389: . ack 1050 win 33580 <nop,nop,timestamp 2574492 6>
10:55:19.512815 PPPoE  [ses 0xfee] colwyn.zhadum.de.16389 > netbsd.hut.fi.ssh: P 1050:1098(48) ack 1853 win 17520 <nop,nop,timestamp 6 2574492> (DF)
10:55:19.628534 PPPoE  [ses 0xfee] netbsd.hut.fi.ssh > colwyn.zhadum.de.16389: P 1853:1901(48) ack 1098 win 33580 <nop,nop,timestamp 2574492 6>
10:55:19.629200 PPPoE  [ses 0xfee] colwyn.zhadum.de.16389 > netbsd.hut.fi.ssh: P 1098:1162(64) ack 1901 win 17520 <nop,nop,timestamp 7 2574492> (DF)
10:55:19.913703 PPPoE  [ses 0xfee] netbsd.hut.fi.ssh > colwyn.zhadum.de.16389: . ack 1162 win 33580 <nop,nop,timestamp 2574493 7>
10:55:20.101120 PPPoE  [ses 0xfee] netbsd.hut.fi.ssh > colwyn.zhadum.de.16389: P 1901:1965(64) ack 1162 win 33580 <nop,nop,timestamp 2574493 7>
10:55:20.101943 PPPoE  [ses 0xfee] colwyn.zhadum.de.16389 > netbsd.hut.fi.ssh: P 1162:1658(496) ack 1965 win 17520 <nop,nop,timestamp 8 2574493> (DF)
10:55:20.313030 PPPoE  [ses 0xfee] netbsd.hut.fi.ssh > colwyn.zhadum.de.16389: . ack 1658 win 33580 <nop,nop,timestamp 2574494 8>
10:55:20.326743 PPPoE  [ses 0xfee] netbsd.hut.fi.ssh > colwyn.zhadum.de.16389: P 1965:2461(496) ack 1658 win 33580 <nop,nop,timestamp 2574494 8>
10:55:20.330987 PPPoE  [ses 0xfee] colwyn.zhadum.de.16389 > netbsd.hut.fi.ssh: P 1658:1754(96) ack 2461 win 17520 <nop,nop,timestamp 8 2574494> (DF)
10:55:20.512677 PPPoE  [ses 0xfee] netbsd.hut.fi.ssh > colwyn.zhadum.de.16389: . ack 1754 win 33580 <nop,nop,timestamp 2574494 8>
10:55:20.533713 PPPoE  [ses 0xfee] netbsd.hut.fi.ssh > colwyn.zhadum.de.16389: P 2461:2493(32) ack 1754 win 33580 <nop,nop,timestamp 2574494 8>
10:55:20.534384 PPPoE  [ses 0xfee] colwyn.zhadum.de.16389 > netbsd.hut.fi.ssh: P 1754:1802(48) ack 2493 win 17520 <nop,nop,timestamp 9 2574494> (DF)
10:55:20.649728 PPPoE  [ses 0xfee] netbsd.hut.fi.ssh > colwyn.zhadum.de.16389: P 2493:2541(48) ack 1802 win 33580 <nop,nop,timestamp 2574494 9>
10:55:20.650127 PPPoE  [ses 0xfee] colwyn.zhadum.de.16389 > netbsd.hut.fi.ssh: P 1802:1866(64) ack 2541 win 17520 <nop,nop,timestamp 9 2574494> (DF) [tos 0x8] 
10:55:20.770733 PPPoE  [ses 0xfee] netbsd.hut.fi.ssh > colwyn.zhadum.de.16389: P 2541:2589(48) ack 1866 win 33580 <nop,nop,timestamp 2574495 9> [tos 0x8] 
10:55:20.771100 PPPoE  [ses 0xfee] colwyn.zhadum.de.16389 > netbsd.hut.fi.ssh: P 1866:1914(48) ack 2589 win 17520 <nop,nop,timestamp 9 2574495> (DF) [tos 0x8] 
10:55:20.912429 PPPoE  [ses 0xfee] netbsd.hut.fi.ssh > colwyn.zhadum.de.16389: . ack 1914 win 33580 <nop,nop,timestamp 2574495 9> [tos 0x8] 
10:55:21.325507 PPPoE  [ses 0xfee] netbsd.hut.fi.ssh > colwyn.zhadum.de.16389: P 2589:2653(64) ack 1914 win 33580 <nop,nop,timestamp 2574496 9> [tos 0x8] 
10:55:21.327344 PPPoE  [ses 0xfee] colwyn.zhadum.de.16389 > netbsd.hut.fi.ssh: P 1914:1946(32) ack 2653 win 17520 <nop,nop,timestamp 10 2574496> (DF) [tos 0x8] 
10:55:21.459977 PPPoE  [ses 0xfee] netbsd.hut.fi.ssh > colwyn.zhadum.de.16389: P 4065:4349(284) ack 1946 win 33580 <nop,nop,timestamp 2574496 10> [tos 0x8] 
10:55:21.460331 PPPoE  [ses 0xfee] colwyn.zhadum.de.16389 > netbsd.hut.fi.ssh: . ack 2653 win 17520 <nop,nop,timestamp 10 2574496> (DF) [tos 0x8] 
10:55:21.460722 PPPoE  [ses 0xfee] netbsd.hut.fi > colwyn.zhadum.de: (frag 1387:4@1440) [tos 0x8] 
10:55:21.477693 PPPoE  [ses 0xfee] netbsd.hut.fi.ssh > colwyn.zhadum.de.16389: . 2653:4061(1408) ack 1946 win 33580 <nop,nop,timestamp 2574496 10> (frag 1387:1440@0+) [tos 0x8] 
10:55:21.477726 PPPoE  [ses 0xfee] netbsd.hut.fi > colwyn.zhadum.de: (frag 1389:4@1440) [tos 0x8] 
10:55:21.494960 PPPoE  [ses 0xfee] netbsd.hut.fi.ssh > colwyn.zhadum.de.16389: . 4349:5757(1408) ack 1946 win 33580 <nop,nop,timestamp 2574496 10> (frag 1389:1440@0+) [tos 0x8] 
10:55:21.495140 PPPoE  [ses 0xfee] netbsd.hut.fi > colwyn.zhadum.de: (frag 1390:4@1440) [tos 0x8] 
10:55:21.511946 PPPoE  [ses 0xfee] netbsd.hut.fi.ssh > colwyn.zhadum.de.16389: . 5761:7169(1408) ack 1946 win 33580 <nop,nop,timestamp 2574496 10> (frag 1390:1440@0+) [tos 0x8] 
10:55:22.713936 PPPoE  [ses 0xfee] netbsd.hut.fi > colwyn.zhadum.de: (frag 1402:4@1440) [tos 0x8] 
10:55:22.731550 PPPoE  [ses 0xfee] netbsd.hut.fi.ssh > colwyn.zhadum.de.16389: . 2653:4061(1408) ack 1946 win 33580 <nop,nop,timestamp 2574498 10> (frag 1402:1440@0+) [tos 0x8] 
10:55:25.712841 PPPoE  [ses 0xfee] netbsd.hut.fi > colwyn.zhadum.de: (frag 1431:4@1440) [tos 0x8] 
10:55:25.730835 PPPoE  [ses 0xfee] netbsd.hut.fi.ssh > colwyn.zhadum.de.16389: . 2653:4061(1408) ack 1946 win 33580 <nop,nop,timestamp 2574504 10> (frag 1431:1440@0+) [tos 0x8] 
10:55:31.712099 PPPoE  [ses 0xfee] netbsd.hut.fi > colwyn.zhadum.de: (frag 1520:4@1440) [tos 0x8] 
10:55:31.730194 PPPoE  [ses 0xfee] netbsd.hut.fi.ssh > colwyn.zhadum.de.16389: . 2653:4061(1408) ack 1946 win 33580 <nop,nop,timestamp 2574516 10> (frag 1520:1440@0+) [tos 0x8] 
10:55:43.711312 PPPoE  [ses 0xfee] netbsd.hut.fi > colwyn.zhadum.de: (frag 1604:4@1440) [tos 0x8] 
10:55:43.728833 PPPoE  [ses 0xfee] netbsd.hut.fi.ssh > colwyn.zhadum.de.16389: . 2653:4061(1408) ack 1946 win 33580 <nop,nop,timestamp 2574540 10> (frag 1604:1440@0+) [tos 0x8] 
10:56:07.708273 PPPoE  [ses 0xfee] netbsd.hut.fi > colwyn.zhadum.de: (frag 1754:4@1440) [tos 0x8] 
10:56:07.726306 PPPoE  [ses 0xfee] netbsd.hut.fi.ssh > colwyn.zhadum.de.16389: . 2653:4061(1408) ack 1946 win 33580 <nop,nop,timestamp 2574588 10> (frag 1754:1440@0+) [tos 0x8] 
10:56:55.701036 PPPoE  [ses 0xfee] netbsd.hut.fi > colwyn.zhadum.de: (frag 2185:4@1440) [tos 0x8] 
10:56:55.719016 PPPoE  [ses 0xfee] netbsd.hut.fi.ssh > colwyn.zhadum.de.16389: . 2653:4061(1408) ack 1946 win 33580 <nop,nop,timestamp 2574684 10> (frag 2185:1440@0+) [tos 0x8] 
10:57:59.693066 PPPoE  [ses 0xfee] netbsd.hut.fi > colwyn.zhadum.de: (frag 2685:4@1440) [tos 0x8] 
10:57:59.710974 PPPoE  [ses 0xfee] netbsd.hut.fi.ssh > colwyn.zhadum.de.16389: . 2653:4061(1408) ack 1946 win 33580 <nop,nop,timestamp 2574812 10> (frag 2685:1440@0+) [tos 0x8] 
10:59:03.685273 PPPoE  [ses 0xfee] netbsd.hut.fi > colwyn.zhadum.de: (frag 3407:4@1440) [tos 0x8] 
10:59:03.703241 PPPoE  [ses 0xfee] netbsd.hut.fi.ssh > colwyn.zhadum.de.16389: . 2653:4061(1408) ack 1946 win 33580 <nop,nop,timestamp 2574940 10> (frag 3407:1440@0+) [tos 0x8] 
11:00:07.677065 PPPoE  [ses 0xfee] netbsd.hut.fi > colwyn.zhadum.de: (frag 3852:4@1440) [tos 0x8] 
11:00:07.694577 PPPoE  [ses 0xfee] netbsd.hut.fi.ssh > colwyn.zhadum.de.16389: . 2653:4061(1408) ack 1946 win 33580 <nop,nop,timestamp 2575068 10> (frag 3852:1440@0+) [tos 0x8] 
11:00:35.070195 PPPoE  [ses 0xfee] colwyn.zhadum.de.16389 > netbsd.hut.fi.ssh: F 1946:1946(0) ack 2653 win 17520 <nop,nop,timestamp 638 2574496> (DF) [tos 0x8] 
11:00:35.180846 PPPoE  [ses 0xfee] netbsd.hut.fi.ssh > colwyn.zhadum.de.16389: . ack 1947 win 33580 <nop,nop,timestamp 2575124 638> [tos 0x8] 

LAN interface of the IP NAT gateway:
10:55:16.498714 PPPoE  [ses 0xfee] colwyn.zhadum.de.16389 > netbsd.hut.fi.ssh: S 565709589:565709589(0) win 16384 <mss 1412,nop,wscale 0,nop,nop,timestamp 0 0> (DF)
10:55:16.615547 PPPoE  [ses 0xfee] netbsd.hut.fi.ssh > colwyn.zhadum.de.16389: S 2400819126:2400819126(0) ack 565709590 win 32768 <mss 1460,nop,wscale 0,nop,nop,timestamp 2574486 0>
10:55:16.615845 PPPoE  [ses 0xfee] colwyn.zhadum.de.16389 > netbsd.hut.fi.ssh: . ack 1 win 17520 <nop,nop,timestamp 1 2574486> (DF)
10:55:16.731603 PPPoE  [ses 0xfee] netbsd.hut.fi.ssh > colwyn.zhadum.de.16389: P 1:53(52) ack 1 win 33580 <nop,nop,timestamp 2574487 0>
10:55:16.732073 PPPoE  [ses 0xfee] colwyn.zhadum.de.16389 > netbsd.hut.fi.ssh: P 1:50(49) ack 53 win 17520 <nop,nop,timestamp 1 2574487> (DF)
10:55:16.854997 PPPoE  [ses 0xfee] netbsd.hut.fi.ssh > colwyn.zhadum.de.16389: P 53:693(640) ack 50 win 33580 <nop,nop,timestamp 2574487 1>
10:55:16.855447 PPPoE  [ses 0xfee] colwyn.zhadum.de.16389 > netbsd.hut.fi.ssh: P 50:594(544) ack 693 win 16880 <nop,nop,timestamp 1 2574487> (DF)
10:55:17.113545 PPPoE  [ses 0xfee] netbsd.hut.fi.ssh > colwyn.zhadum.de.16389: . ack 594 win 33580 <nop,nop,timestamp 2574487 1>
10:55:17.113840 PPPoE  [ses 0xfee] colwyn.zhadum.de.16389 > netbsd.hut.fi.ssh: P 594:618(24) ack 693 win 17520 <nop,nop,timestamp 2 2574487> (DF)
10:55:17.294757 PPPoE  [ses 0xfee] netbsd.hut.fi.ssh > colwyn.zhadum.de.16389: P 693:1117(424) ack 618 win 33580 <nop,nop,timestamp 2574488 2>
10:55:17.327662 PPPoE  [ses 0xfee] colwyn.zhadum.de.16389 > netbsd.hut.fi.ssh: P 618:1034(416) ack 1117 win 17520 <nop,nop,timestamp 2 2574488> (DF)
10:55:17.513284 PPPoE  [ses 0xfee] netbsd.hut.fi.ssh > colwyn.zhadum.de.16389: . ack 1034 win 33164 <nop,nop,timestamp 2574488 2>
10:55:19.284032 PPPoE  [ses 0xfee] netbsd.hut.fi.ssh > colwyn.zhadum.de.16389: P 1117:1853(736) ack 1034 win 33580 <nop,nop,timestamp 2574492 2>
10:55:19.343598 PPPoE  [ses 0xfee] colwyn.zhadum.de.16389 > netbsd.hut.fi.ssh: P 1034:1050(16) ack 1853 win 17520 <nop,nop,timestamp 6 2574492> (DF)
10:55:19.512480 PPPoE  [ses 0xfee] netbsd.hut.fi.ssh > colwyn.zhadum.de.16389: . ack 1050 win 33580 <nop,nop,timestamp 2574492 6>
10:55:19.512815 PPPoE  [ses 0xfee] colwyn.zhadum.de.16389 > netbsd.hut.fi.ssh: P 1050:1098(48) ack 1853 win 17520 <nop,nop,timestamp 6 2574492> (DF)
10:55:19.628534 PPPoE  [ses 0xfee] netbsd.hut.fi.ssh > colwyn.zhadum.de.16389: P 1853:1901(48) ack 1098 win 33580 <nop,nop,timestamp 2574492 6>
10:55:19.629200 PPPoE  [ses 0xfee] colwyn.zhadum.de.16389 > netbsd.hut.fi.ssh: P 1098:1162(64) ack 1901 win 17520 <nop,nop,timestamp 7 2574492> (DF)
10:55:19.913703 PPPoE  [ses 0xfee] netbsd.hut.fi.ssh > colwyn.zhadum.de.16389: . ack 1162 win 33580 <nop,nop,timestamp 2574493 7>
10:55:20.101120 PPPoE  [ses 0xfee] netbsd.hut.fi.ssh > colwyn.zhadum.de.16389: P 1901:1965(64) ack 1162 win 33580 <nop,nop,timestamp 2574493 7>
10:55:20.101943 PPPoE  [ses 0xfee] colwyn.zhadum.de.16389 > netbsd.hut.fi.ssh: P 1162:1658(496) ack 1965 win 17520 <nop,nop,timestamp 8 2574493> (DF)
10:55:20.313030 PPPoE  [ses 0xfee] netbsd.hut.fi.ssh > colwyn.zhadum.de.16389: . ack 1658 win 33580 <nop,nop,timestamp 2574494 8>
10:55:20.326743 PPPoE  [ses 0xfee] netbsd.hut.fi.ssh > colwyn.zhadum.de.16389: P 1965:2461(496) ack 1658 win 33580 <nop,nop,timestamp 2574494 8>
10:55:20.330987 PPPoE  [ses 0xfee] colwyn.zhadum.de.16389 > netbsd.hut.fi.ssh: P 1658:1754(96) ack 2461 win 17520 <nop,nop,timestamp 8 2574494> (DF)
10:55:20.512677 PPPoE  [ses 0xfee] netbsd.hut.fi.ssh > colwyn.zhadum.de.16389: . ack 1754 win 33580 <nop,nop,timestamp 2574494 8>
10:55:20.533713 PPPoE  [ses 0xfee] netbsd.hut.fi.ssh > colwyn.zhadum.de.16389: P 2461:2493(32) ack 1754 win 33580 <nop,nop,timestamp 2574494 8>
10:55:20.534384 PPPoE  [ses 0xfee] colwyn.zhadum.de.16389 > netbsd.hut.fi.ssh: P 1754:1802(48) ack 2493 win 17520 <nop,nop,timestamp 9 2574494> (DF)
10:55:20.649728 PPPoE  [ses 0xfee] netbsd.hut.fi.ssh > colwyn.zhadum.de.16389: P 2493:2541(48) ack 1802 win 33580 <nop,nop,timestamp 2574494 9>
10:55:20.650127 PPPoE  [ses 0xfee] colwyn.zhadum.de.16389 > netbsd.hut.fi.ssh: P 1802:1866(64) ack 2541 win 17520 <nop,nop,timestamp 9 2574494> (DF) [tos 0x8] 
10:55:20.770733 PPPoE  [ses 0xfee] netbsd.hut.fi.ssh > colwyn.zhadum.de.16389: P 2541:2589(48) ack 1866 win 33580 <nop,nop,timestamp 2574495 9> [tos 0x8] 
10:55:20.771100 PPPoE  [ses 0xfee] colwyn.zhadum.de.16389 > netbsd.hut.fi.ssh: P 1866:1914(48) ack 2589 win 17520 <nop,nop,timestamp 9 2574495> (DF) [tos 0x8] 
10:55:20.912429 PPPoE  [ses 0xfee] netbsd.hut.fi.ssh > colwyn.zhadum.de.16389: . ack 1914 win 33580 <nop,nop,timestamp 2574495 9> [tos 0x8] 
10:55:21.325507 PPPoE  [ses 0xfee] netbsd.hut.fi.ssh > colwyn.zhadum.de.16389: P 2589:2653(64) ack 1914 win 33580 <nop,nop,timestamp 2574496 9> [tos 0x8] 
10:55:21.327344 PPPoE  [ses 0xfee] colwyn.zhadum.de.16389 > netbsd.hut.fi.ssh: P 1914:1946(32) ack 2653 win 17520 <nop,nop,timestamp 10 2574496> (DF) [tos 0x8] 
10:55:21.459977 PPPoE  [ses 0xfee] netbsd.hut.fi.ssh > colwyn.zhadum.de.16389: P 4065:4349(284) ack 1946 win 33580 <nop,nop,timestamp 2574496 10> [tos 0x8] 
10:55:21.460331 PPPoE  [ses 0xfee] colwyn.zhadum.de.16389 > netbsd.hut.fi.ssh: . ack 2653 win 17520 <nop,nop,timestamp 10 2574496> (DF) [tos 0x8] 
10:55:21.460722 PPPoE  [ses 0xfee] netbsd.hut.fi > colwyn.zhadum.de: (frag 1387:4@1440) [tos 0x8] 
10:55:21.477693 PPPoE  [ses 0xfee] netbsd.hut.fi.ssh > colwyn.zhadum.de.16389: . 2653:4061(1408) ack 1946 win 33580 <nop,nop,timestamp 2574496 10> (frag 1387:1440@0+) [tos 0x8] 
10:55:21.477726 PPPoE  [ses 0xfee] netbsd.hut.fi > colwyn.zhadum.de: (frag 1389:4@1440) [tos 0x8] 
10:55:21.494960 PPPoE  [ses 0xfee] netbsd.hut.fi.ssh > colwyn.zhadum.de.16389: . 4349:5757(1408) ack 1946 win 33580 <nop,nop,timestamp 2574496 10> (frag 1389:1440@0+) [tos 0x8] 
10:55:21.495140 PPPoE  [ses 0xfee] netbsd.hut.fi > colwyn.zhadum.de: (frag 1390:4@1440) [tos 0x8] 
10:55:21.511946 PPPoE  [ses 0xfee] netbsd.hut.fi.ssh > colwyn.zhadum.de.16389: . 5761:7169(1408) ack 1946 win 33580 <nop,nop,timestamp 2574496 10> (frag 1390:1440@0+) [tos 0x8] 
10:55:22.713936 PPPoE  [ses 0xfee] netbsd.hut.fi > colwyn.zhadum.de: (frag 1402:4@1440) [tos 0x8] 
10:55:22.731550 PPPoE  [ses 0xfee] netbsd.hut.fi.ssh > colwyn.zhadum.de.16389: . 2653:4061(1408) ack 1946 win 33580 <nop,nop,timestamp 2574498 10> (frag 1402:1440@0+) [tos 0x8] 
10:55:25.712841 PPPoE  [ses 0xfee] netbsd.hut.fi > colwyn.zhadum.de: (frag 1431:4@1440) [tos 0x8] 
10:55:25.730835 PPPoE  [ses 0xfee] netbsd.hut.fi.ssh > colwyn.zhadum.de.16389: . 2653:4061(1408) ack 1946 win 33580 <nop,nop,timestamp 2574504 10> (frag 1431:1440@0+) [tos 0x8] 
10:55:31.712099 PPPoE  [ses 0xfee] netbsd.hut.fi > colwyn.zhadum.de: (frag 1520:4@1440) [tos 0x8] 
10:55:31.730194 PPPoE  [ses 0xfee] netbsd.hut.fi.ssh > colwyn.zhadum.de.16389: . 2653:4061(1408) ack 1946 win 33580 <nop,nop,timestamp 2574516 10> (frag 1520:1440@0+) [tos 0x8] 
10:55:43.711312 PPPoE  [ses 0xfee] netbsd.hut.fi > colwyn.zhadum.de: (frag 1604:4@1440) [tos 0x8] 
10:55:43.728833 PPPoE  [ses 0xfee] netbsd.hut.fi.ssh > colwyn.zhadum.de.16389: . 2653:4061(1408) ack 1946 win 33580 <nop,nop,timestamp 2574540 10> (frag 1604:1440@0+) [tos 0x8] 
10:56:07.708273 PPPoE  [ses 0xfee] netbsd.hut.fi > colwyn.zhadum.de: (frag 1754:4@1440) [tos 0x8] 
10:56:07.726306 PPPoE  [ses 0xfee] netbsd.hut.fi.ssh > colwyn.zhadum.de.16389: . 2653:4061(1408) ack 1946 win 33580 <nop,nop,timestamp 2574588 10> (frag 1754:1440@0+) [tos 0x8] 
10:56:55.701036 PPPoE  [ses 0xfee] netbsd.hut.fi > colwyn.zhadum.de: (frag 2185:4@1440) [tos 0x8] 
10:56:55.719016 PPPoE  [ses 0xfee] netbsd.hut.fi.ssh > colwyn.zhadum.de.16389: . 2653:4061(1408) ack 1946 win 33580 <nop,nop,timestamp 2574684 10> (frag 2185:1440@0+) [tos 0x8] 
10:57:59.693066 PPPoE  [ses 0xfee] netbsd.hut.fi > colwyn.zhadum.de: (frag 2685:4@1440) [tos 0x8] 
10:57:59.710974 PPPoE  [ses 0xfee] netbsd.hut.fi.ssh > colwyn.zhadum.de.16389: . 2653:4061(1408) ack 1946 win 33580 <nop,nop,timestamp 2574812 10> (frag 2685:1440@0+) [tos 0x8] 
10:59:03.685273 PPPoE  [ses 0xfee] netbsd.hut.fi > colwyn.zhadum.de: (frag 3407:4@1440) [tos 0x8] 
10:59:03.703241 PPPoE  [ses 0xfee] netbsd.hut.fi.ssh > colwyn.zhadum.de.16389: . 2653:4061(1408) ack 1946 win 33580 <nop,nop,timestamp 2574940 10> (frag 3407:1440@0+) [tos 0x8] 
11:00:07.677065 PPPoE  [ses 0xfee] netbsd.hut.fi > colwyn.zhadum.de: (frag 3852:4@1440) [tos 0x8] 
11:00:07.694577 PPPoE  [ses 0xfee] netbsd.hut.fi.ssh > colwyn.zhadum.de.16389: . 2653:4061(1408) ack 1946 win 33580 <nop,nop,timestamp 2575068 10> (frag 3852:1440@0+) [tos 0x8] 
11:00:35.070195 PPPoE  [ses 0xfee] colwyn.zhadum.de.16389 > netbsd.hut.fi.ssh: F 1946:1946(0) ack 2653 win 17520 <nop,nop,timestamp 638 2574496> (DF) [tos 0x8] 
11:00:35.180846 PPPoE  [ses 0xfee] netbsd.hut.fi.ssh > colwyn.zhadum.de.16389: . ack 1947 win 33580 <nop,nop,timestamp 2575124 638> [tos 0x8] 

So "tcpdump" saw 62 packets out the outer interface but only 50 on the
inner one. What is happening here?

	Kind regards

-- 
Matthias Scheler                                  http://scheler.de/~matthias/