100% CPU utilization on a Cisco 887VA

Some time ago I wrote a blogpost about using a Cisco 887VA router on a XS4All (dutch ISP) connection. The original article is mostly in Dutch, but I’ll keep this one in English since it will probably help users all over the world.

A couple of days ago I got an e-mail from somebody who read my blogpost and asked me if the 887VA was able to handle more then 25Mbit. I never really tested it since I thought the copper-cable in our office wasn’t that good. During a download I logged into the router and saw that the CPU was 94% utilized!

The VDSL line was however online at 38Mbit, so how could this happen? Was the router underpowered?

I couldn’t wrap my head around it. A brand new VDSL router from Cisco couldn’t handle just 25Mbit? Something had to be wrong.

Some searching brought me to the Cisco Support Forums and one of the suggestions was to turn on CEF. A Cisco technology to improve Layer 3 performance.

Logging in to the router showed me indeed that CEF was disabled for both IPv4 and IPv6.

no ip cef
no ipv6 cef

Enabling CEF was simple:

conf t
ip cef
ipv6 cef

And voila! I suddenly was able to use the full 38Mbit with just ~50% CPU load.

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Wido den Hollander

I am the CTO at PCextreme B.V. and i will keep this blog just to post some interesting information about my daily work on Linux (and other) systems.