Multicast Routing

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Sep 16th, 2007
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I have two network entities which have multicast routing configured and working on both them. They have a link between both of them that is currently not enabled for multicast routing thus keeping the two multicast domains completely separate.

At this point I need to have multicast routing working between the both, but only on one specific address ( Rather then just adding an ip pim dense-mode (sparse-mode,etc) statement to the interfaces and then routing all of the multicast addresses is there a way to route that one address between the two?

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Richard Burts Sun, 09/16/2007 - 17:55
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I am not aware of a way to route the multicast between the two without enabling PIM (sparse, dense, sparsedense whichever). My suggestion would be to enable PIM (whichever mode you like) and then to apply an access list on the interfaces of this link. The access list would:

permit ip host any

deny ip any

permit ip any any

This will have the effect of allowing your desired multicast, denying any other multicast, and permitting all other IP. Of course if you have an existing access list on these interfaces then this logic needs to be incorporated into the existing logic.



Kevin Dorrell Sun, 09/16/2007 - 23:21
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I think you will also need to allow any multicasts that your routing protocols need. (Or will those bypass the access list?) Typically it should be safe to permit ip At the minimum you will need permit ip host to allow the PIM, plus perhaps .27 and .28 if you are running sparse-mode.

Kevin Dorrell


cjnwodo Mon, 09/17/2007 - 08:17
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Sounds to me like you need to enable PIM on the interface and then apply a multicast boundary to it.


access-list 10 permit host


int f0/0

ip multicast boundary 10


Depending on the version of IOS you are using you might need to specify the direction of the multicast boundary in or out.

mhurley131 Fri, 09/21/2007 - 18:03
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Quick question on the multicast boundary command...

Is the access list for multicast addresses that i want to cross the boundary or for addresses that i want stopped? The documentation ive found on the command is not very clear on that.

Based on the comment here it looks like i allow only the addresses i want, but the cisco documentation make it seem like you allow the addresses you want filtered.

cjnwodo Mon, 09/24/2007 - 00:17
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In my experience i've used it to permit the multicast groups that I want allowed.

Note: If you use it on an IOS that does not specify the direction [ip multicast boundary 10 in or ip multicast boundary 10 out] then the command is bidirectional.

Pavel Bykov Mon, 09/24/2007 - 03:01
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Theoretically, MSDP was built for exactly your scenario. You can interconnect your multicast domains and allow only needed multicast group (e.g. using "msdp sa-filter")

Please refer to the following documents:

Hope this helps


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