Policy Routing - Performance Loss?

[mlsommer]

What kind of performance hit will I see on a Cat6506 running in pure IOS mode when I am exchanging full BGP routes with 2 ISPs and have policy routing enabled? Basically, what I'm interested in is will I have less latency by getting rid of the policy routing altogether and simply load-balancing between the two ISPs to which I'm dual homed? I understand that by utilizing policy routing, CEF & DCEF are not able to be used. With this in mind I assume that latency will likely increase. Is this true? and to what extent?

I would be extremely greatful to anyone who can offer me a little insight and/or a link to some thorough documentation or whitepapers on this.

Thanks,

Matt

[thisisshanky]

With policy routing enabled, process switching is used. So latency is there, compared to techniques such as Fast and CEF switching. You can additionally enabled Fast switched Policy routing, to improve latency in switching.

[m.venkatesan]

I was recently playing with PBR and did a performance analysis. It wasn't really bad with either Fast-switching or netflow. PBR supports CEF and netflow. If you don't configure any caching, then it will the router. The following links has some good info...

http://www.cisco.com/warp/public/cc/pd/iosw/prodlit/ntfo_wp.htm

Mannan

[vcjones]

Whether or not policy routing forces process switching will depend upon the IOS release, the hardware platform, and sometimes even the specific policy routing commands used. Most of the policy routing commands which force process switching are documented as such in the command reference, but it may not always be obvious.

As always, test and measure carefully as your mileage may vary :-)

Vincent C Jones

www.networkingunlimited.com

[mlsommer]

Thanks for all of your good suggestions. I'm going to keep digging, testing, and measuring. I plan on trying fast switching mode first.

Thanks again,

Matt