[127700] in North American Network Operators' Group
Re: Rate Limiting on Cisco Router
daemon@ATHENA.MIT.EDU (Danny McPherson)
Thu Jul 8 22:04:39 2010
From: Danny McPherson <danny@tcb.net>
In-Reply-To: <AANLkTim30hkm4wtMXXCQYGsWRq-v_3lqMHonNBDF9ZnR@mail.gmail.com>
Date: Thu, 8 Jul 2010 20:04:11 -0600
To: nanog@nanog.org
Errors-To: nanog-bounces+nanog.discuss=bloom-picayune.mit.edu@nanog.org
On Jul 8, 2010, at 4:05 PM, Alan Bryant wrote:
> Thanks again for all the responses to my previous post.
>=20
> We have a Cisco 7206VXR router with IOS of 12.4(12) and a PA-POS-1OC3
> card ofr our OC3.
>=20
> 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.
>=20
> 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.
>=20
> Any advice?
If your issue is cost for rates larger than 80 Mbps then you probably =
want=20
to find out what applications are using the bulk of the bandwidth and=20
either adjust your budget, or their performance expectations and =
allocate
network resources expressly. Flow data (even local cache analysis v.=20
exporting) would help you glean some of this, but external longer term=20=
analysis would surely be more useful - and there are lots of way you can=20=
do that - and use the data to either justify more budget or cull =
offending=20
applications.
As others have noted, rate *limiting* is usually indiscriminate and =
often=20
results in non-determinism and far less 'goodput' than rate-shaping. If
hardware constraints with those WAN-side PHY devices are gating, you=20
could always do it on the LAN side, and perhaps much more selectively=20
based on which application and associated network transaction traffic is=20=
the most valuable to your business and in your operating environment.
Given, you didn't talk about asymmetries and egress traffic policy =
tweaking=20
at the CPE to induce desired ingress levels is usually a science in and =
of=20
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=20
worst case you align network resource allocation with critical business=20=
applications first via LAN-side rate-shaping functions - or AUPs, or....
-danny
