Redundant multicast routing

Mark Smith markrefresh12 at
Tue Jan 3 15:01:27 UTC 2012


What's your recipe to implement redundant multicast (stub) routing?
Let's think about the simplest scenario. We have 2 routers, R1 and R2
and 3 ip networks. All 3 networks are directly connected to both
routers and the routers are performing unicast routing between
networks using VRRP as the redundancy protocol. Let's disregard L2
redundancy here and assume it works. Same goes with igmp snoop.

net1:, VRRP .254, R1 .1, R2 .2
net2:, VRRP .254, R1 .1, R2 .2
net3:, VRRP .254, R1 .1, R2 .2

Say multicast source is in net1 and receiver in net2.

If I did not need redundancy in multicast, I would just configure all
interfaces on R1 as pim passive and it would (probably) work. But if I
want the multicast routing to be redundant, what should I do?

If I add the R2 interfaces as pim passive, the multicast is forwarded
to net2 (and net3) twice because R1 and R2 do not know about each
other. I tested this.
If I configure all R1 and R2 interfaces as pim dense, the destination
receives multicast fine, but it is flooded between R1 and R3 2 or 3
times (because pim dense floods the multicast to all pim neighbors and
R1 and R2 are pim neighbors in all 2 networks). So, core links are
unnecessarily consumed. I tested this, too.

One choice could be to use pim sparse and configure R1 and R2 to be
anycast RPs using loopback interface and configure MSDP peering
between them. But given the simplicity of the topology, this seems
unnecessarily complex configuration. I have not tested this yet.

Maybe MVR could be solution but I think it will cause stream
multiplication too. I have not tested MVR yet either.

I would like to keep the recipe as vendor agnostic as possible.

Thanks for help :)

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