Telnet Disconnects - Please help!

Mike Bird mgb-ubuntu at
Sun May 25 17:05:09 UTC 2008

On Sun May 25 2008 03:32:27 Harald Milz wrote:
> I know the PNG with the filtered pcap doesn't seem that complete, but
> Bertelsmann has a very strict policy about data privacy, so I am unable to
> post the complete pcap.

The first packet displayed already has a zero window.  We need to
determine why.  Without that information we can only guess.

For example, something may be blocking ICMP packets necessary for
the router to discover the PMTU.  If this were the case, full-size
packets would never reach the laptop but smaller packets would
arrive, causing Ubuntu to sit with a full window and repeatedly
ack in order to try to stimulate the retransmission of the missing

If this is the case (and ICMP blocks are a common mistake) the bad
filter could be anywhere between the router and the T61 inclusive.
If it only happens in Ubuntu but not Windows on the same laptop,
I'd check the laptop's firewall first.

However, the pattern of incrementing acks without data from the
router would (if confirmed by the totality of the data stream)
suggest some kind of TCP bug.

--Mike Bird

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