TCP Stall

Richard B. Johnson (root@analogic.com)
Sat, 5 Apr 1997 20:45:22 -0500 (EST)

This message is in MIME format. The first part should be readable text,
while the remaining parts are likely unreadable without MIME-aware tools.
Send mail to mime@docserver.cac.washington.edu for more info.

---1295196120-33695938-860291122=:606
Content-Type: TEXT/PLAIN; charset=US-ASCII

I have now found the EXACT sequence of events that leads to the
TCP Stall. It is repeatable. I don't know WHY it happens, however
I now know WHAT is happening. The event that leads to the stall is
the first line in the attached file.

I enabled the character generator (chargen, port 19) so I have a
continuous stream of characters. The remote (slow-speed) end of
the link executes:

# telnet chaos chargen

A process on my ppp server, that can listen on the Ethernet backbone
executes:

# tcpdump -nlpS -tt host chaos >tcp.dmp

It looks as though a cache-entry has expired, the host sends an ARP
request to find the hardware address of the already established client.

The host gets very confused but eventually continues to send data 31
seconds later.

So the new questions are; "Should an ARP cache entry expire on an established
connection?", and; "If this happends, what bad things can happen?".

Cheers,
Dick Johnson
-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
Richard B. Johnson
Project Engineer
Analogic Corporation
Voice : (508) 977-3000 ext. 3754
Fax : (508) 532-6097
Modem : (508) 977-6870
Ftp : ftp@boneserver.analogic.com
Email : rjohnson@analogic.com, johnson@analogic.com
Penguin : Linux version 2.1.31 on an i586 machine (66.15 BogoMips).
Warning : I read unsolicited mail for $350.00 per hour. Supply billing address.
-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-

---1295196120-33695938-860291122=:606
Content-Type: APPLICATION/octet-stream; name="dump.gz"
Content-Transfer-Encoding: BASE64
Content-ID: <Pine.LNX.3.91.970405204522.606B@chaos.analogic.com>
Content-Description:
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---1295196120-33695938-860291122=:606--