Link DOWN detection on 3750

[alanwright1]

Hi Folks,

I have a small test network where i have two 3750's, as routers. In the middle is a linux router. I send traffic from say R1.

Client-----R1-----LxRTR----R2---Server

If the linux router puts the interface DOWN (IFDOWN)between itself and R1, the ARP entry of the LxRTR remains in R1's arp cache, however, if the same command is done on Lx RTR on the interface to R2, R2 correctly detects the link DOWN and removes the entry from ARP cache.

Any ideas why this occurs only on one side?

PS. They have the same IOS image 12.2.40SE IPSVCS

TIA

Alan

[John Blakley]

Alan,

I'm not sure if this applies, but I had an earlier version of the IOS on my 3750 stack. ARP entries wouldn't time out without clearing arp. I updated to 12.2(46)SE, and it resolved the issue (or so it seemed). There was a document describing the bug somewhere, but I haven't been able to find it again.

I would try to update your IOS (regardless if it works on one and not the other).

Found it: http://supportwiki.cisco.com/ViewWiki/index.php/Host_connectivity_or_ping_issues_due_to_ARP_or_CEF_table_changes_in_Catalyst_3750_switch_stack

HTH,

John