MAC-to-IP address ARP table?

Unanswered Question
May 5th, 2010

The SNMP MIB entry ipNetToMediaPhysAddress gives the MAC address from the ARP table, referenced by the IP.  Is there a table available anywhere in some router MIB that would give the equivalent of "MediaPhysAddressToipNet" (reverse) information so that an IP address in the ARP table could be referenced using the MAC address?

RFC1213 section 3.6 alludes to a future document that would define a MIB for CLNP and it would contain two tables for mappings in both directions.  But I've not been able to find anything else about that.

I'm trying to avoid pulling the entire ARP table from the router (several thousand entries makes it take about 90 seconds and it drives the CPU to 100%) just to get a single MAC-to-IP address mapping when that info is needed.

--Scott

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Joe Clarke Wed, 05/05/2010 - 22:32

I haven't run across any such object, and a quick check of my 15.0 router yields nothing I missed.

You might consider doing periodic collection of the ARP table (e.g. when most users are logged into the network) to have a cache through which to search for this kind of information.  This is how the Campus Manager User Tracking application works.  By default, it polls the ARP table (along with swithc MAC/CAM tables) at 10:00 and 14:00 to build a table of all connected users.  From this one can search for IPs, MACs, and even usernames.

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