SRE External Gig port for WCCP traffic?

[Tammy Cox]

Has anyone been successful with using the external Gig port on the SRE modules for WCCP traffic?  Has anyone tried it?

I'd like to reduce the CPU on my ISR-G2 routers that have the SRE modules running WCCP GRE.  I'd like to use the external gig port on the SRE module for the WCCP traffic, which will allow me to use WCCP L2.  Is this even feasible?  Or maybe I just need to add WCCP L2 on an SRE as a New Feature request to Cisco?

According the to Cisco documentation....

The external service-module interface can be used to monitor LAN traffic. You can also select the external interface as the management interface for the SM. The external interface cannot be used for downloading applications.

Visible only to the SM software on the Cisco SM-SRE, the external service-module interface is the Gigabit Ethernet interface connector on the Cisco SM-SRE faceplate. The external interface supports data requests and data transfers from outside sources, and it provides direct connectivity to the LAN through an RJ-45 connector.

[Michael Korenbaum · Accepted solution]

Tammy,

What is preventing you from configuing WAAS on SRE with L2 WCCP / Mask assignment via the internal interface?   This is totally feasible.

If you are trying to decrease CPU utilization on your router, don't expect switching from GRE to L2 to make a drastic difference.  The ISR G2 is a software based platform, as such WCCP (whether L2 or GRE) is processed by the CPU with CEF assistance. 

True removing the GRE encapsulation will save some processing overhead, but in the end it's the PPS (packets per second) your router is handling that's driving the CPU.

Remember when you add WCCP / WAAS to the flow it's no longer packet in/ packet out on the router.  Compressed data in on WAN, out to WAAS, uncompressed from WAAS back to Router, out on the LAN, then the reverse... uncompressed data on the LAN in to the router, out to WAAS, compressed from WAAS out to the router, then out on the WAN.  So depending on the compression observed you will see > 2x the amount of traffic being processed by the router. 

[Tammy Cox]

Hi Michael,

That is excellent news.  I know in the past few years we've tried it on older code than what we are running now and it didn't work - but I don't recall if that was a WAAS code or router IOS issue.

You are correct in that it is the PPS that is primary driver, but every little bit of reduction we implement helps.  I also heard back via a query to our Cisco SE that the external SRE interface would work for the WCCP traffic as well.

I did a quick test in the lab on an SRE running WAAS 5.1.1 and 4.4.3 for the L2 on a 2911 running 15.1(1)T.  It did work on both, although the cli command output on the SRE is different between the two versions and not always clear.  However, running the sh ip wccp sum on the router is reflecting the L2 Redirect.

Thanks again!