What is the ARP table size on a Catalyst 6500 with Supervisor 720-3B

[rstever]

I am trying to find out how many ARP entries a Catalyst 6500 with Supervisor 720-3B modules can hold.  I am looking into a problem that seems to be related to ARP and CAM table aging timer mismatches due to asymmetrical traffic patterns in a LAN switching environment.  I understand one of the options to resolve this is to increase the CAM aging timer to 4 hours to match the default ARP timer.  When discussing this solution, a question came up with regards to how many ARP entries can be held on the switch.  Based on this an alternative was to lower the ARP timer to 5 minutes to match the default CAM timer.

I could not find a document on CCO that described the maximum number of ARP entries that can be cached.  We did some checking and we are running around 5,000 cached ARP entries on our distribution layer switches where the default gateway services for workstations reside.  I have heard 128,000 entries from one source, but I cannot point to any authoritative document to back that up.  I have also heard that the ARP table size might increase if you have more than 256MB DRAM, but again I cannot point to any authoritative document to back that up.

[Shashank Singh]

Hi Randy,

There is no spec available as such for ARP table  but following are the specs for mac address table and routes for this platform:

•The PFC3 supports a theoretical maximum of 64 K MAC addresses (32 K MAC addresses recommended maximum).

•The PFC3 partitions the hardware FIB table to route IPv4 unicast, IPv4 multicast, MPLS, and IPv6 unicast and multicast traffic in hardware.

The defaults for PFC3B are:

–IPv4 unicast and MPLS—192,000 routes

–IPv4 multicast and IPv6 unicast and multicast—32,000 routes

For more information, visit:

http://www.cisco.com/en/US/docs/switches/lan/catalyst6500/ios/12.2SXF/native/release/notes/hardware.html

Hope this helps,

Shashank

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[Shashank Singh]

Hi Randy,

If you suspect you are running out of memory space with your ARP entries, do the following command and check the available and used memory for storing mac-addresses.

'sh tcam count'

Cheers,

Shashank

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