Inbound TCP Circuits over PPP Stall; MTUs and Kppp
paulus at cs.anu.edu.au
Mon Sep 27 10:14:35 EST 1999
Randall R Schulz <rrschulz at cris.com> wrote:
> By using tcpdump, I have discovered what seems to be a relevant fact:
> When the stream stalls, the sending side (always the remote) is
> resending the same range of bytes (sequence numbers) over and over
> again with an inter-packet arrival time that increases gradually
> until it reaches about two minutes where it holds until one side or
> the other gives up and closes the stream. Each such packet has the
> PUSH flag set and elicits an ACK from my system, but for whatever
> reason, the remote just keeps sending repetitions of a packet
> containing the same range of sequence numbers (with a total of 1448
> data bytes each).
This sounds like the remote system isn't getting the ACKs (or they are
getting corrupted). Try putting the `novj' option in your ~/.ppprc
file and see if that makes any difference.
> I have captured the tcpdump output from one of these "sessions"
> (beginning when I clicked a FTP URL link in Navigator through until I
> cancelled the stalled transfer after several repetitions at the
> two-minute inter-packet arrival time. There are 140 lines of tcpdump
> output. If anybody can make use of this in diagnosing the problem,
> I'd be happy to send it...
I would be interested to see it.
> This problem is easily repeated,
Hopefully we can track it down then.
> I'd like to try changing my PPP MTU from 1500 to 1514, but I don't
> know where to control it under kppp and the documentation doesn't
> mention it.
Try making yourself a ~/.ppprc file containing the line `mru 1514'.
In fact the MTU is determined by the MRU (max receive unit) that the
peer asks for so you can't directly control it except to give a
maximum value with the mtu option.
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