[c-nsp] ip multicast rate-limit

[Tim Stevenson]

My answers below for 6500/sup720 only:

At 11:36 PM 3/27/2006, Hank Nussbacher quipped:
>I am wondering what is up with the "ip multicast rate-limit" command.  A
>few gotcha's from Cisco:

This command, ip multicast rate-limit, is not supported & never has 
been on 6500/7600.

>a) doesn't work on 12.2(18)SXE4:
>
>petach-tikva-gp(config-if)#ip multicast ?
>    boundary       Boundary for administratively scoped multicast addresses
>    helper-map     Broadcast to Multicast map OR Multicast to ip-address map
>    netflow        NetFlow accounting for multicast
>    rate-limit     Rate limit multicast data packets
>    tagswitch      Enable IP Multicast Tagswitching
>    ttl-threshold  TTL threshold for multicast packets
>
>petach-tikva-gp(config-if)#ip multicast rate-limit ?
>    in   Rate limit incoming packets
>    out  Rate limit outgoing packets
>
>petach-tikva-gp(config-if)#ip multicast rate-limit in 40000
>   "ip multicast rate-limit" command is not supported

This is correct.


>Was introduced in 11.0 so should be available and the CLI shows it as
>available.  No altrernate command suggested.  See below.

THe correct alternative is an MQC policy that classifies & polices 
multicast traffic (ie, using ACLs, class-maps, policy maps, service policy).


>b) On:
><http://www.cisco.com/en/US/products/ps6350/products_command_reference_book09186a008042def5.html>
>the left hand menu shows a link for "IP Multicast Commands: ip multicast
>rate-limit through ip urd", which is a mistake and should be 'route-limit'
>to 'urd'.

No idea on this one - you point to a 12.4 IOS doc, which of course is 
not supported on 6500.


>c) On:
><http://www.cisco.com/en/US/products/hw/routers/ps368/products_command_reference_chapter09186a0080172751.html>
>it lists the command for 12.2SX as being "mls ip multicast rate-limit" yet
>the link to the actual page shows the command as being now "mls rate-limit
>multicast ipv4..."  Looks like someone has been playing fast and loose with
>the CLI syntax and changing their minds every few months :-)

Yes, this syntax was changed to accomodate IPv6 multicast when it was 
added. This command is TOTALLY different from any of the above, this 
configures the various h/w rate limiters for the RP CPU, meaning it 
throttles back multicast packets of various types that are being 
punted to the RP for whatever reason.

>d) Following the multicast trail, I see the mls command has an igmp option
>such as "mls rate-limit multicast ipv4 igmp" for rate limiting igmp pps,
>yet 12.2(18)SXE4  one can still do

The above is actually a "Layer 2" rate limiter - that is to say, it 
is a CPU rate limiter that applies to the SP CPU. It globally rate 
limits IGMP & PIM (yes PIM) packets redirected to the SP CPU for IGMP 
snooping purposes.

>petach-tikva-gp(config-if)#ip igmp limit ?
>    <1-64000>  Max Allowed State on this interface

This is a software only rate limiter that limits the amount of IGMP 
state allowed on an L3 interface in IOS.

>Couldn't Cisco put all multicast limiters in one spot in the CLI?

This is my job security... :\  But seriously, I am not sure I agree 
that all RLs of any kind should drop under one CLI chain. Here we are 
talking about IGMP software state, hardware rate limiters, and 
control plane RLing. Shouldn't these fall into their appropriate chains?

>   Can't
>Cisco indicate a command has been deprecated and what the new command
>should be?  Can't Cisco check their documentation?

Agree that often the docs are misleading, incomplete, or in some 
cases wrong. We correct the docs if this appears to be the case. If 
you find an error, there is a feedback button on virtually every 
cisco.com page, in my experience this works in most cases. For 6500 
stuff, I know the writers personally & can ask them to change stuff. 
What exactly would you suggest be changed per the above?

Tim


>Thanks,
>Hank
>
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Tim Stevenson, tstevens at cisco.com
Routing & Switching CCIE #5561
Technical Marketing Engineer, Catalyst 6500
Cisco Systems, http://www.cisco.com
IP Phone: 408-526-6759
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