[Ilugc] Weird network problem
- From: girish1729@xxxxxxxxx (Girish Venkatachalam)
- Date: Mon Jul 31 17:22:35 2006
--- Joe Steeve <joe_steeve@xxxxxxx> wrote:
Girish Venkatachalam wrote:
Try clearing the ARP caches completely once in a
while. You can try
clearing the Cisco router ARP entry then.
Other than that what does ifdown/ifup do? It might
do much more but
this seems to be a good reason to me.
Hmm., I'll have to check the ARP cache of the 'cisco
router' next time
this happens. But when the issue happens., the
'Cisco router' routes all
other packets correctly to the 'ISP router'., so
that address could not
be screwed. It is possible that the cache entry for
the 'mailserver' is
screwed. However, when the issue happens., the
'Cisco router' responds
to pings from the 'mailserver'. That means., it does
have the correct
MAC address entry in the cache.
Anywayz., I'll check this the next time the issue
happens.
One good thing to do would be to figure out how
often ur mail server
talks out on the network. Dumping tcpdump to a
file and analyzing
what goes wrong when would help.
This is something that should be helpful. I did not
try this. I can do
this on the 'firewall' box.
You cannot rule out a hardware issue here in the NIC
chip of the ethernet card. What card is it? Realtek?
Intex?
You can check for hardware problem by stressing the
receive path of the NIC. Only recv causes interrupts
and NICs normally expose their problem that way.
Try this at the mailserver machine.
$ scp -r user@cisco-router:/usr .
If you find that after a few minutes nothing happens
then you can rule out hardware issue.
If you get a checksum error or network disconnect in
the hub , then it is time to get your card replaced.
Anyway pls observe the problem for some time and
theorize after you have data. Observe tcpdump output
for a while. What particular packet exchange causes
this behavior? Or is it after a certain period of
time?
As Arthur Conan Doyle says,
" It is a capital mistake to theorize before you have
all the facts. You cannot build bricks without clay."
:-)
I enjoyed this thread.
All the best! Kindly let us know what the problem
turned out to be in the end.
regards,
Girish
--
.o. A proud GNU user
..o
ooo [W] http://www.joesteeve.org/
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