High CPU load on Cisco 877 and 878 while downloading

Hi,

I have recently tested performance of Cisco 876 router (which is basically the same as your 877 but for ADSL-over-ISDN) using Agilent N2X tester. My observation is that top performance of this router at small packets is roughly 6Mbps, while with large packets it could go a bit higher - slightly over 10Mbps. So this is at most half of the line rate you have.

Same with 878. I have tested 878 with QoS enabled, the performance decreases dramatically - it can't even do 2Mbps on small packets. According to Cisco performance datasheet, 870 routers can deliver upto 12.8Mbps and upto 25Kpps in ideal conditions and this values can never be exceeded, but will decrease as you add features (NAT, firewall, routing, QoS etc.)

Don't expect anything much greater in this price range of routers. I have tested also DrayTek 2800 and 2900 series routers - they're even worse. While Cisco 870 ISR routers perform much better as soon as packet size increases to 128Byte, with DrayTek packet size has to be at least 768Byte to get decent troughput.

If you use 20Mbps line, you have to get something like Cisco 1800 series router.

Hope this helps.

Cheers, iLya

I agree that this sounds like too much for an 870 however it is worth checking that there is not something amiss.

Please post:-

sh run ! < -- please sanitise.

!sh tech ipmulticast ! < -- produces a password-removed config and not ! < -- too much else if you do not have m'cast configured

!when the router is under stress sh proc cpu ! < -- first few lines.

!when it has stopped frowarding traffic sh mem ! < -- first few lines sh buff ! < -- all

oops, my mistake. The other router was this 876.

But thanks a lot for your clear answer. I tested a little bit yesterday and as long as I stay below 80% of CPU-usage ( around 12 mbit downloading) the router stays online.

If you want I can run the tests just to make sure. Maybe later today.

thanks,

Jos

Today I called the reseller and he confirmed all this:

-the maximum routeable traffic (he used other words, but I hope you'll understand this...) is for the 800 series 12 mbit.

-if I want to use the full bandwidth, I need a 1800 series.

Anyway, thanks for your answers! Maybe I'll put the router in the freezer or something, see what happens then... ;-)

BTw,if the reason why the router "did not remain online" while you were moving more data than it can handle, was that its CPU was pegged in interrupt mode, then you should be able to reconfigure it so that it can provide CPU cycles to process activity ... something like:

scheduler allocate 3000 1000

Cheers,

Aaron