Rate Limiting on Cisco Router

Fri Jul 9 02:04:11 UTC 2010

On Jul 8, 2010, at 4:05 PM, Alan Bryant wrote:

> Thanks again for all the responses to my previous post.
> 
> We have a Cisco 7206VXR router with IOS of 12.4(12) and a PA-POS-1OC3
> card ofr our OC3.
> 
> The problem we have now is that we are only paying for 80 MB/s of the
> OC-3, and the ISP is leaving the capping of it up to us. I have
> googled and the only things I can find is that you can not do a real
> cap on this type of interface.
> 
> We have tried the rate-limit command with various parameters and we
> are unable to keep it at 80. I have read that this is not the correct
> way to do it, but I'm not sure what is.
> 
> Any advice?

If your issue is cost for rates larger than 80 Mbps then you probably want 
to find out what applications are using the bulk of the bandwidth and 
either adjust your budget, or their performance expectations and allocate
network resources expressly.  Flow data (even local cache analysis v. 
exporting) would help you glean some of this, but external longer term 
analysis would surely be more useful - and there are lots of way you can 
do that - and use the data to either justify more budget or cull offending 
applications.

As others have noted, rate *limiting* is usually indiscriminate and often 
results in non-determinism and far less 'goodput' than rate-shaping.  If
hardware constraints with those WAN-side PHY devices are gating, you 
could always do it on the LAN side, and perhaps much more selectively 
based on which application and associated network transaction traffic is 
the most valuable to your business and in your operating environment.
Given, you didn't talk about asymmetries and egress traffic policy tweaking 
at the CPE to induce desired ingress levels is usually a science in and of 
it's self - but alas, if one must turn the steam valves ;-)

I can't see application of any rate-limiting policies indiscriminately be
desirable in any business environment, and suggest that if budget constrained 
worst case you align network resource allocation with critical business 
applications first via LAN-side rate-shaping functions - or AUPs, or....

-danny