[c-nsp] Brief CPU spikes on 6500 Sup 720

[Jon Lewis]

On Wed, 14 Jul 2010, Phil Mayers wrote:

>> mac-address-table aging-time 14400
>> 
>> http://www.ciscopress.com/articles/article.asp?p=336872
>
> Or of course drop the ARP timeout:
>
> int VlanX
>  arp timeout 290

I haven't tracked down the exact issue, but we've seen issues when using 
too short an arp timeout on a 6500 vlan interface.  Sometimes customers 
will ask for really short arp timeouts to cope with failover systems that 
change an IPs MAC address.

The vlan in question had an arp timeout of 60s and had a couple of KVM 
servers with 100 or so virtual machines.  Especially when a large number 
of VMs started up, we'd see periods of packet loss.  My assumption is that 
the sup720-3bxl can only handle so much arp activity on a vlan.  There was 
nothing in the config to artificially limit arp traffic.

----------------------------------------------------------------------
  Jon Lewis                   |  I route
  Senior Network Engineer     |  therefore you are
  Atlantic Net                |
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