RE: Odd Networking problem.

I have known this issue to happen with certain hardware vendors (Nortel) where the ARP table is not accurate. Out of curiosity, can you list the network equipment in the middle?

-----Original Message-----
From: [email protected] [mailto:[email protected]] On Behalf Of Keith
Sent: Tuesday, June 21, 2011 3:29 PM
To: [email protected]
Subject: Odd Networking problem.

I have two machines, both of them connected to a switch on the same vlan.
Vlan is a /27. There are a few other machines on this vlan as well.

Both the machines in question are running:

Linux 2.6.24-etchnhalf.1-686-bigmem #1 SMP Thu Nov 5 02:48:47 UTC 2009
i686 GNU/Linux

Identical hardware/software on both servers, 1U 3550 IBM machines.

Problem is one of the servers goes unreachable for hours or minutes at a time. Just the one was have as the 'spare' server thank goodness.

This is the odd part. The /27 the server is on is carved out of a /24 we use for network links (/30) and some other Vlans carved out in /29, /28 and /27s.

When this server goes unreachable to the rest of the network, the server can still ping out to any other IP in the /24 that its /27 is part of.

And any other machine that has an IP on a Vlan part of the same /24 can ping the server.

But any other device on the network not part of that /24 can not ping the server and the server can not ping outside of that /24.

None of the other servers on this vlan have any problems, it is just this one machine.

Here is the arp entry for the server on the switch (3560): (IP obfuscated)
Internet  192.168.191.102        125   0021.5edc.a598  ARPA   Vlan40

3 mins later I ping the 192.168.191.102 from the switch and the age of the ARP entry is 0:

Sending 5, 100-byte ICMP Echos to 192.168.191.102, timeout is 2 seconds:
!!!!!

Arp entry:
Internet  192.168.191.102          0   0021.5edc.a598  ARPA   Vlan40

And almost right away the server is reachable from anywhere.

What causes the ARP entry to reset to 0 besides the ARP timer expiring the entry? A few mins ago on the switch the arp entry was 15 mins old, now it shows that arp entry is only 8 mins old. I thought I understood arp, but I guess I don't understand the behaviour as well as I thought.

Thanks,
Keith
--
Eat sushi frequently. - Avi
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-- 
Eat sushi frequently. - Avi
[email protected] is the human contact address.
[email protected] is the list posting address.
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