arp cache time

[FranzR]

Dear Community,

when does a arp entry in the cache of a vsp-Switch deleted?
Can this be modified?

Our problem is that we use a 60 minutes lease time at the DHCP server. And sometimes the NAC System reports a ARP spoofing event if DHCP server offers a new client a IP adress because of lease time. But in the arp cache of the Switch this IP belongs to the older MAC adress.

Thanks

Franz

[WillyHe · Accepted solution]

Hello Franz,

The default arp time-out for VSP and ERS switches is 6 hours, you can see that when executing "show ip arp", at the end of the table following information is provided.

====================================================================================================

IP Arp Extn - GlobalRouter

====================================================================================================

MULTICAST-MAC-FLOODING    AGING(Minutes)    ARP-THRESHOLD

----------------------------------------------------------------------------------------------------

disable                                           360                          500

c: customer vid u: untagged-traffic

30 out of 35 ARP entries displayed

ARPs on TX-NNI: Current = 0, re-ARP count = 4

If you like it is possible to change the ARP time-out

SA-02:1(config)#ip arp timeout ?

<1-32767> Arp lifetime in minutes

When using VRF's you must change ARP time-out for each VRF.

hope this helps

regards
WillyHe