[c-nsp] rate limiting multicast

[Hank Nussbacher]

At 09:56 AM 16-03-05 -0600, John Kristoff wrote:

See:

ip multicast rate-limit {in | out} [video | whiteboard] [group-list 
access-list] [source-list access-list] kbps

<http://www.cisco.com/univercd/cc/td/doc/product/software/ios122/122cgcr/fiprmc_r/mult/1rfmult2.htm#wp1078547>

-Hank

>On Wed, 16 Mar 2005 10:26:35 +0100 (CET)
>"Mikael Carlander" <rip at kth.se> wrote:
>
> > Most ISP's are now rate-limiting Multicast. My question is: When you limit
> > Multicast, are you limiting CPU or bandwidth? and more importantly, are
> > you limiting by percentage or a static number?
>
>Can you provide references to the claim that most ISP's are rate
>limiting multicast traffic?  I'd be curious in how specifically.  It
>may be that certain types of multicast data and/or control traffic is
>being limited, but it matters as to which one you are talking about.
>
>Generally speaking, you may be limiting both CPU somewhere and link
>usage (what you call bandwidth).  If you set rate limits on edge
>interfaces for anything over UDP to 224/4 for example, you are potentially
>saving capacity on links that multicast may have been forwarded onto.
>In addition, you may also be limiting multicast state created on the
>router with the rate limit, or ones further downstream, due to the sender
>driven state mechanisms used in typical multicast configurations.  This
>is often the case when worms have indiscriminately scanned 224/4.
>
>Most rate limit knobs use a fixed number, but since you are often
>talking about a rate limit of capacity on a fixed speed link, you
>can think of it as a percentage if you'd like to.
>
>John
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