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igmp ssm-map static

I was kind of curious on something. I recently changed my ssm static maps to directly specify which multicast source a particular multicast would be coming from. This is coming from a provider outside of my network.


ip igmp ssm-map static 40

ip igmp ssm-map static 41

ip igmp ssm-map static 42

I then have specific multicast with them access-lists:

access-list 41 permit

This obviously creates a really nice sh ip mroute entry with a one to one mapping. What I had before was a more generic access-list with all the hosts pointint to the same access-list:

ip igmp ssm-map static 30

ip igmp ssm-map static 30

ip igmp ssm-map static 30

Then i created a more generic access-list like:

access-list 30 permit

which was really nice. The only problem is that it created a mapping in the mroute table for each specific host. That is what the router is supposed to do and was expected. The problem with the way i'm doing it now is that my multicast provider could change a multicast to a different source. I would have the source address in my table, but I don't have the friendly access-list like I had with the /16. I was wondering if there is any harm on doing it the way I had it in the first place even though I could actually get up to 20 entries of sources and one is really only active. I hope this makes sense, just trying to figure out the easiest way to accomplish this with ssm or the best way I guess. Looking for opinions.

Cisco Employee

Re: igmp ssm-map static


The question is, do you want to send the same request to 3 different sources or only one. I think the way you were doing things before is a bit harder to maintain but it is worth it.


Harold Ritter
Sr. Technical Leader
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igmp ssm-map static


I have a question about SSM DNS and static mapping.

Let's say we already have SSM with DNS mapping and it works fine. I want now to add a new source and source group

but I do not want to add a DNS record. Can I create a static mapping without disabling the working SSM DNS mapping configuration?

I found this on but I have to be sure that I will not disable the working SSM DNS mappings!

Static SSM Mapping

SSM static mapping enables you to configure the last hop router to use a static map to determine the sources sending to groups. Static SSM mapping requires that you configure access lists (ACLs) to define group ranges. The groups permitted by those ACLs then can be mapped to sources using the ip igmp static ssm-map command.

You can configure static SSM mapping in smaller networks when a DNS is not needed or to locally override DNS mappings that may be temporarily incorrect. When configured, static SSM mappings take precedence over DNS mappings.

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