Oliver Lehmann writes:


[...]

> 13:13:28.839003 IP (tos 0x0, ttl 64, id 56001, offset 0, flags [DF],
> proto TCP (6), length 60) 10.1.1.1.50984 > 10.1.1.2.echo: S,
> cksum 0xb417 (correct),
> 903547536:903547536(0) win 65535 > sackOK,timestamp 12024138 0>
> 0x0000: 0145 0000 3cda c140 0040 0649 f60a 0101 .E..<..@.@.I....
> 0x0010: 4500 003c dac1 4000 4006 49f6 0a01 0101 E..<..@.@.I.....
> 0x0020: 0a01 0102 c728 0007 35db 0a90 0000 0000 .....(..5.......
> 0x0030: a002 ffff b417 0000 0204 0200 0103 0303 ................
> 0x0040: 0402 080a 00b7 794a 0000 0000 ......yJ....
> 13:13:29.062298 IP (tos 0x0, ttl 254, id 65456, offset 0, flags [none],
> proto TCP (6), length 44) 10.1.1.2.echo > 10.1.1.1.50984: S,
> cksum 0xb461 (correct),
> 1262663520:1262663520(0) ack 4294967185 win 2048
> 0x0000: 0045 0000 2cff b000 00fe 06a7 160a 0101 .E..,...........
> 0x0010: 4500 002c ffb0 0000 fe06 a716 0a01 0102 E..,............
> 0x0020: 0a01 0101 0007 c728 4b42 b760 ffff ff91 .......(KB.`....
> 0x0030: 6012 0800 b461 0000 0204 0200 `....a......
>
> I don't know how the package the old system sends out should look like
> but it seems to be wrong - otherwise the echoping would have detected it
> I'd guess.


One random thing I would try: turn off all of the newer TCP/IP options
on your modern box, like selective acknowledgement (SACK), path MTU
discovery (PMTU-D), timestamping, and window scaling. The older
system may not understand them, or they may cause the modern system to
require a particular set of options back that it doesn't get. Look in
your logs for anything interesting. Look at your interface stats with
ifconfig to see if there are any clues (if the number of errors
increases that's an interesting clue). See what happens when you try
to initiate a connection from the older server to the newer. See if
your OS has any network debugging options you can turn on.

Hope this helps,

----Scott.