Can I change ARP timers on a router? (7301)

[jwbensley]

A link went down to another router (R2 @ 10.224.0.6). However I thought I was having a one way traffic issue down the link as the ARP entry for R2 was still present in R1, but R1 was not in R2.

As you can see from the output below an ARP entry for R2 was still present in R1, its says 253 minutes, but the link had been down for around the last 120 minutes or so.

Is there something I can change on R1, a 7301 running c7301-advipservicesk9-mz.122-33.SRC, to stop these ARP entries `hanging` around like this?

This is the console output just as the link came back up;

R1#show arp 10.224.0.6

Protocol  Address          Age (min)  Hardware Addr   Type   Interface

Internet  10.224.0.6            253   001a.a1b0.1cad  ARPA   GigabitEthernet0/0.807

R1#

R1#

R1#

Sep  6 12:32:22.613: %BGP-5-ADJCHANGE: neighbor 10.224.0.6 Up

R1#

R1#

R1#show arp 10.224.0.6

Protocol  Address          Age (min)  Hardware Addr   Type   Interface

Internet  10.224.0.6              0   001a.a1b0.1cad  ARPA   GigabitEthernet0/0.807

[Alessio Andreoli · Accepted solution]

Hi J,

below the interface you can type arp time-out as follow:

http://www.cisco.com/en/US/docs/ios/ipaddr/command/reference/iad_arp.html#wp1011700

http://www.cisco.com/en/US/docs/ios/12_1/iproute/command/reference/1rdipadr.html

check the default on your device to avoid to set it again!

Alessio

[John Blakley]

On the interface, you should be able to change the arp timeout with "arp timeout ".

HTH,

John

[ciscoamit_497]

Hi Bensley,

By default on cisco routers, ARP time is set to 4 hrs...hence u need to manually configured it under per interface basis...

Command shown by the J is perfect..

Regards,

Amit

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[jwbensley]

Thanks all for the input. Obivous answer there

On a side note, does anyone think you should change the ARP timer by default? Do people recommend lowering ARP timmers as standard practice? If yes, then why, if no, then why?

Thank you.

[ciscoamit_497]

Hi Ben,

On router, we are not supposed to change it bcoz it increases the router cpu utilization..if arp time-out is configured lower than default..but if necessary then u can chqange it as ur own way....