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Multicast between real servers behind the CSM


I'm looking to get multicasting working between real servers that are behind the CSM.

I'll attached the router config as an example of how the CSM is configured. Note, that we have static routes in place to direct traffic to the real servers from the router to the CSM.

Through a lot of testing, i've found some interesting results, and and i'll explain them as 2 senarios:

Senario 1: no SVI created on the router

In this setup, i have been able to get multicasting working between the real servers on vlan (386) only when i use certain multicast addresses. For example or or alike. If i use or alike, multicasting between the real servers don't work!

How are these IP addressses treated differently? Why do some addresses work, and others don't?

Senario 2: create an SVI vlan 386 on the router

In this setup, creating a SVI with an IP Address and ip pim sparse mode enabled, results in multicasting working for any multicast address. As such load balancing to the real servers continue to work. However, i've noticed that from some subnets traffic to the real servers doesn't get through e.g. SSH etc. Investigations found that the IP address configured on the SVI was presenting a different route!

- What could be a possible fix?

Note, going with senario 2, i was looking to put in place a policy map that routes any traffic coming into interface 386 to a next hop IP of, which is the same next hop IP as defined by the static routes.

Would be very useful if you could shed some light on this issue!




Re: Multicast between real servers behind the CSM

If you are not aware of, I would like to explain you different classifications of Multicast addresses. - --------> Reserved Link Local addresses(Ex: Multicast addresses used for routing protocols like OSPF, EIGRP etc). - ---------> Li9mited-scope addresses(just like private addresses).So, these cannot be forwarded outside to the internet by edge routers. - -----------> Globally scoped addresses. These are the multicast addresses used by the companies to route between different organisations and across the internet. - ---------------> Source-Specific Multicast address. - ------------->GLOP addresses used as multicast addresses between two different AS.

I think in your scenario, 239.0. network because there is an edge router between your 2 servers and one server should be a registered ip address.This may also be a reason but still there can be more than 1 reason.

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