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SubjectRe: TCP stalls in 2.0.33 and 2.1.x
David S. Miller writes:
> Date: Wed, 18 Mar 1998 23:53:38 +1100
> From: Richard Gooch <rgooch@atnf.CSIRO.AU>
>
> Nope, the ftp client is running on machine B (2.1.90), which has an
> EtherNet connection to machine A (2.1.86), which is the local
> router (via SLIP) to a CISCO terminal server, which is on the
> departmental LAN. Trust me: I know what keyboard I'm using :-)
>
> The trace still makes no sense then. The connection was completed
> correctly by both machines, and the SunOS FTP server did not send one
> packet containing data.
>
> Sniff the wire at the SunOS box, someone else is dropping packets. I
> bet the SLIP line is hosed, the MTU is incorrect, and the SunOS FTP
> server is sending data packets larger than the MTU of the SLIP end,
> and the CISCO router is dropping things. Doing tcpdump at the Linux
> host, in this case, only gives half the story.

Possibly there are MTU problems. I've got a programme which I can use
to send UDP packets around. If I send 1024 byte packets from machine C
(2.1.90-pre3) to machine A (2.1.86, my router at home), I get 0% loss.
If I send 2048 byte packets, I get 100% packet loss. I make sure I
don't send packets faster than what the SLIP link will handle.
I get the same results if I send from machine C to machine B (2.1.90).

As I understand it, if your packet travels links with different MTUs
(such as when you go from EtherNet to SLIP), then packets are
fragmented and reassembled. This works even for UDP, correct?

The MTU on my SLIP link is 255. I'll check tomorrow what the CISCI
terminal server is set to, but I think it should be higher than
that. Would that cause a problem?

Regards,

Richard....

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