ARP & mac address entries

[SpongeRob]

Hello,

Under what circumstance would a mac-address show up in the arp tables but not in the mac-address table?  when I look at the arp table for an particular address is has a corresponding mac-add, when I show mac-add | i mac-add it does not show!

[milan.kulik]

Hi,

don't forget the ARP cache timer is 4 hours by default, while forwarding MAC table timer is 5 minutes!

So if the end device was not sending any traffic for last 5 minutes, the entry is removed from the MAC address table.

But it remains in the ARP cache much longer!

HTH,

Milan

[SpongeRob]

Thanks Milan - if I clear arp and it is again in the arp table should it then be in the mac-add table ?

[milan.kulik · Accepted solution]

Yes, it should.

As your device should send an ARP request and get an ARP response to fill the ARP cache entry again at the moment it needs to send any data to the end device.

HTH,

Milan

[SpongeRob]

Milan thanks for the replies.  Evidently it is an Avaya phone system that "we are not suppose to see", however immediately following a clear arp it is in the arp table yet absent from the mac-addr.

Best Regards,

[fb_webuser]

ARP stand for address resolutions protocol. Arp convert Mac add to Ip add. RARP just opposite to arp.

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Posted by WebUser Awnish Kumar

[fb_webuser]

ARP maintains a list of both IP addresses and matching MAC addresses called the ARP cache. These caches are available on individual network adapters

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Posted by WebUser Awnish Kumar