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Old 02-04-2010, 11:37 AM
"Joel Merrick"
Default Issues with SYN on Lenny

Hi all,

Seeing a strange problem exhibited after a recent dist-upgrade of an
exim server.

We see connections hanging when connecting to port 25 running on the
2.6.26 kernel version.

Running a tcpdump on the server shows that a syn packet is received, but
there's no ack or anything. Using the etch kernel doesn't cause this
issue either, which negates any issue with exim, iptables or named and
the like.

I'm wondering if there's been any changes to the tcp/ip stack or the way
the kernel handles syn cookies etc..

The server is under heavy utilization, so I'm wondering if we're
tripping an arbitrary value somewhere in /proc ?

Any tips greatly appreciated!

Joel Merrick
Systems Administrator, Zen Internet
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