On 9/12/07, Jun Salen <nokijun@xxxxxxxxx> wrote:
> On 9/11/07, Jun Salen <nokijun@xxxxxxxxx> wrote:
> > >Hi List,
> > >
> > >My Mail/Proxy server has from time to time refuse
> to
> > >accept accept network connection. If I restart the
> > >network service, the service will again start to
> > >accept connection but after some time will again
> > >refuse connection. I use CentOS 4.5 with Squid,
> > >DansGuardian, Postfix. Please can someone point me
> > >what are the possible cause of this. Thank you.
> >
> > In addition to my posting above. When I make ping to
> > other machine from the server, the server will again
> > restore and accept connection. This is weird, so my
> > temporary solution is to let the server continually
> > ping other machine. Please help. Thanks again.
> >
>
> Ping is a very cheap and acceptable solution !
>
> Anyway you'r certainly curious about the problem :-)
> This is a problem about ARP request.
> Maybe another machine with low activity share the same
> IP or your
> swith/hub
> is badly configured !
> You can use arping to detect any device with the same
> IP and tcpdump
> to look for arp request."arp -an" will show you the
> arp table.
>
> Regards
>
> > junji
> > aisalen.wordpress.com
> > Linux Registered User #253162
> >
> > Send instant messages to your online friends
> http://uk.messenger.yahoo.com
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> >
>
>
> --
> Alain Spineux
> aspineux gmail com
>
>
> -----------------------
>
> When I do /sbin/arp -an in the server box it does not
> contain entries for ip address where the server, it is
> ok?
I have the same here, I'm not surprised.
> I observed that when I ping the server from other
> machine, it replies but from time to time displays
> time-out. We use this server for our mail and proxy so
> it is affecting us when time outs occur. Tsk tsk.
Every time the server ping (or open an IP connection) one of your
client, it "announce" its MAC address on the network. Switches and
bridges will learn this information for some minutes and later
redirect client responses or new connections directly to your server.
When the MAC cache is expired, switches have to learn by them self,
and depending
the network topology, the configuration of the switch, or some bug in
the switch itself this could fail.
Try to replace your switch.
>
>
> junji
> aisalen.wordpress.com
> Linux Registered User #253162
>
> Send instant messages to your online friends http://uk.messenger.yahoo.com
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> http://lists.centos.org/mailman/listinfo/centos
>
--
Alain Spineux
aspineux gmail com
May the sources be with you
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