IP ARP Question

[john.wright]

We have two Layer 3 switches one of which is the main switch for all layer 3 switching. And the other is backup.

We monitor the SVI's with hsrp between the two switches.

I noticed today that when I do sh ip arp on the back up L3 switch that there are a lot of IP entries.

The primary L3 switch has many more (over 2400) but I was suprised to see so many entries (well over 800 in the backup L3 switch. It is an active switch with backup servers connected to it as well as firewall and router.

Is it normal to have that many arp entries in a backup L3 switch?

[Joseph W. Doherty · Accepted solution]

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Posting

My guess would be the backup switch is recording ARP announcments, like gratious ARP annoucements.

[Jon Marshall]

John

In addition to Joseph's reply it may also be to do with your topology.

So you may be running HSRP for the clients which means they all go via the active switch but if some destination subnets are remote and reached via the router for example the return traffic could go to either L3 switch unless of course you are also running HSRP on the "other side" as well.

If the return traffic goes to the backup switch it should simply arp out for the clients.

So it depends on your setup really.

Jon