dst cache overflow

[Stephan =?iso-8859-1?Q?Engstr=F6m?=]

I have a busy webserver that stops responding to network traffic when
running for 7-10 days. First the server will gradually slow down and
then all network traffic will stop. The syslog is full of:

    dst cache overflow
    NET: 173 messages suppressed.

The machine is alive and well but to start network traffic I have to
reboot the machine.
Doing a 'netstat -t -n -o' says that there are 5364 connections in
LAST_ACK state, is this some kind of DOS or what?

I have some information (netstat and some /proc output) if more
information is needed.

Thanks

Stephan Engström