tlug: tcpdump and networking problem

[Neil Booth <NeilB@example.com>]

Here is the output of tcpdump on my PPP connection to my ISP,
comparing RH 5.2 and RH 6.0.  My networking problem with 2.2.x kernels
has not gone away, despite a clean RH 6.0 install to which I had only
done the minimum of entering my ISPs phone number, login name,
password and primary DNS server.  So there is no real room for me to
have screwed up.

Here is RH 5.1 2.0.36 kernel, which achieves the "+OK" from telnetting
the POP3 server on port 110:-

22:36:31.799404 tc-1-095.ariake.gol.ne.jp.1063 > ns01.dns.gol.com.domain: 38594+ A? popmail.gol.com. (33)
22:36:31.999404 ns01.dns.gol.com.domain > tc-1-095.ariake.gol.ne.jp.1063: 38594* 3/4/4 (238)
22:36:31.999404 tc-1-095.ariake.gol.ne.jp.4831 > pp02.mail.gol.com.pop-3: S 3179524889:3179524889(0) win 512 <mss 1474> [tos 0x10]
22:36:32.139404 pp02.mail.gol.com.pop-3 > tc-1-095.ariake.gol.ne.jp.4831: S 596482816:596482816(0) ack 3179524890 win 61320 <mss 1460> (DF)
22:36:32.139404 tc-1-095.ariake.gol.ne.jp.4831 > pp02.mail.gol.com.pop-3: . ack 1 win 32428 (DF) [tos 0x10]
22:36:32.329404 pp02.mail.gol.com.pop-3 > tc-1-095.ariake.gol.ne.jp.4831: P 1:39(38) ack 1 win 61320 (DF)
22:36:32.349404 tc-1-095.ariake.gol.ne.jp.4831 > pp02.mail.gol.com.pop-3: . ack 39 win 32428 (DF) [tos 0x10]

And exactly the same procedure for RH 6.0 2.2.5 gives:-

22:30:36.992170 203.216.42.119.1027 > 165.76.16.2.domain: 54611+ A? popmail.gol.com. (33)
22:30:37.200028 165.76.16.2.domain > 203.216.42.119.1027: 54611 3/4/4 (246) (DF)
22:30:37.201252 203.216.42.119.1078 > 203.216.5.32.pop-3: S 2446288621:2446288621(0) win 32428 <mss 1474,sackOK,timestamp 8815740 0,nop,wscale 0> (DF)
22:30:37.340018 203.216.5.32.pop-3 > 203.216.42.119.1078: S 526016256:526016256(0) ack 2446288622 win 60816 <mss 1460,nop,wscale 0,nop,nop,timestamp 568693 8815740> (DF)
22:30:37.340078 203.216.42.119.1078 > 203.216.5.32.pop-3: . ack 1 win 32428 <nop,nop,timestamp 8815754 568693> (DF)

Where it stalls; the effect being I don't get the "+OK" message.
Comparing the two, it appears to me that all is the same, except that
2.2.x does not receive the "P" (Push) packet from my ISP.  To me, a
networking newbie, that means that either my ISP didn't get my most
recent acknowledgement "ack 1", or that the reply they sent was
dropped either by my modem or kernel.

My modem is an external AIWA PV-BW5601 56K.  In both cases above,
tcpdump reports *no* packets dropped by the kernel.

Any ideas, e.g. where to look next, would be hugely appreciated.

Cheers,

Neil.
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