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IP ARP Question

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?

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Super Bronze

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Posting

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

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Super Bronze

DisclaimerThe Author of this

Disclaimer

The Author of this posting offers the information contained within this posting without consideration and with the reader's understanding that there's no implied or expressed suitability or fitness for any purpose. Information provided is for informational purposes only and should not be construed as rendering professional advice of any kind. Usage of this posting's information is solely at reader's own risk.

Liability Disclaimer

In no event shall Author be liable for any damages whatsoever (including, without limitation, damages for loss of use, data or profit) arising out of the use or inability to use the posting's information even if Author has been advised of the possibility of such damage.

Posting

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

Hall of Fame Super Blue

JohnIn addition to Joseph's

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

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