3845 PBR Performance

[Muhammad Kashif Siddiqui]

I am having one ISR-3845 Router. I am having AdvanceIPServices-12.4 (24)T5 IOS. This router is terminating 100Mbps Internet link. Currently we are having around 60Mbps traffic as average.

Due to some topology change I have to apply PBR to my internal traffic to switch (Source based Routing) some traffic to other router. Before doing any change I want to check the PBR Performance of 3845 Router as I believe it is a software based platform and will all the PBR traffic will be circuit switched (Will not use CEF or Fastswitching).

Can anyone advice what will be the impact on Router with increase (from 60Mbps to 100Mbps) in traffic or If you can share some PBR performance document ?

[Joseph W. Doherty · Accepted solution]

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PBR will add to your processing overhead, but doubtful anyone can easily predict the incremental additional load it will add.

I recall on some platforms, and IOS versions, the Cisco documentation will note specific PBR commands that will cause process switching.

I also recall (?) there might also be a PBR kind of cache feature on some platforms and IOSs.

[Jon Marshall · Accepted solution]

As Joseph says it is difficult to be precise about the amount of overhead it will introduce.

However from IOS 12.x onwards PBR has been supported with CEF so as far as I am aware you should not see it process switching.

See this link for details -

http://www.cisco.com/c/en/us/td/docs/ios/12_2/qos/configuration/guide/fqos_c/qcfpbr.html#wp1005373

Jon

[Muhammad Kashif Siddiqui]

Hi Jon,

You have shared a very good document which negate my statement about PBR Process switching. Thanks for this.

Can you further help in finding any document which can describe the PBR throughput over ISR Routers or more specifically 3845 ?

Thanks/Regards

[Jon Marshall]

I don't think you will find those figures because it is not like the VPN throughput for example. 

PBR is still forwarding packets with CEF it's just overriding the routing table as such.

So the only thing i can think of is the complexity of your acl ie. keep it as simple as possible.

If your device was a L3 switch then you need to be more careful as some PBR options can cause packets to be sent to the main CPU which degrades the performance but you are not dealing with a hardware based device.

Sorry I can't be more precise but with software based devices, as Joseph said, it's difficult to quantify.

Jon