[c-nsp] 7200vxr-npe400/512mb - how much BGP?

[Justin M. Streiner]

On Mon, 14 Apr 2008, Skeeve Stevens wrote:

> Just how much BGP should a 7200vxr-NPE400 with 512MB of RAM be able to
> handle.
> 
> The router currently says "Total: 466497056, Used: 200153224, Free:
> 266343832"
>
> When should I start worrying about how big the tables are growing and so on?

512 MB is the minimum I'd consider using for a router that will be 
carrying full BGP feeds, but in this case, the limiting factor might not 
be memory availability, but rather the CPU, since everything in the 7200 
series is done in software.  Do you notice your CPU usage spiking 
periodically (around once a minute), and is a large chunk of the CPU tied 
up un the BGP Scanner process?

If you have a tool for graphing and trending stuff like that over time 
(MRTG, Cricket, many others), you may want to set up something to monitor 
that CPU utilization, paying attnetion to both the 5 second and 5 minute 
CPU utilization values in the MIBs.  The 5 second value will help you 
catch transient spikes that get washed out of the 5-minute average 
values.  The output ends up more closely resembling the output of "show 
proc cpu hist".  When the utilization starts regularly getting close to 
100%, it's time to think about an upgrade.

I wouldn't worry so much about one or two errant spikes, but when things 
regularly get that high, it could manifest itself in the form of increased 
latency in getting traffic through the box, or if things get bad enough, 
the router starts missing BGP update messages or similar messages for your 
IGP, and sessions/adjacencies can start dropping, which only makes the CPU 
thrashing problem worse.

jms