Re: Multicast AnyCast + MSDP

/"As I have configured RPs statically on the 4 routes, I do not have any
form of load balancing and Redundancy of RPs. Correct?"/

Technically you could configure your static RP mapping such that
different RPs are used for different groups in the MCAST domain and this
would achieve a very crude form of load balancing.

E.g.

ip access-l stand MCAST-GROUPS1
permit 224.0.0.0 7.255.255.255
!
ip access-l stand MCAST-GROUPS2
permit 232.0.0.0 7.255.255.255
!
ip pim rp-addr 3.3.3.3 MCAST-GROUPS1
!
ip pim rp-addr 6.6.6.6 MCAST-GROUPS2

There's no redundancy in the example above and depending on the number
of MCAST groups and how they are carved up, it could become a mess as
times goes on.

Now when using Anycast, you're adding redundancy and possibly
load-balancing, but this is all dependant on your underlying routing
protocol. Anycast will ensure that the multicast trees are built towards
the "closest" RP (closest being determined by the RIB / Routing Protocol).

I'm hoping that the following scenario might help to explain the concept
of MSDP and why you might want / need to use it:

We've got two RP's in the network using an Anycast IP address.

One of the RP's is located close to a multicast source. The other RP is
located close to the receivers for that multicast source.

If the multicast network is configured correctly, the RP closest to the
multicast receivers will have an (*,G / Shared Tree) multicast state
entry with an OIL (Outgoing Interface List) directing multicast traffic
towards the receivers. Essentially, the RP knows that there are
multicast receivers on the network wanting a multicast stream.

When the multicast source starts transmitting, the RP closest to it will
end up with the (S,G) state entry for the source. And this is where the
disconnect happens and our multicast traffic doesn't flow as we'd like
it to. We are now in a situation where one RP knows about the multicast
receivers and another RP knows about the multicast senders. We need some
way of telling the RP (where the multicast clients are located), that
there is a multicast source in the network (which has registered with
another RP). This is one of the uses for MSDP. MSDP is used to advertise
the (S,G) entries between RPs.

In the scenario above, once we configure MSDP, the the RP (closest to
the multicast clients) gets the SA. It can now build a (S,G) tree to the
multicast source and traffic will start to flow through to the multicast
clients (As a side note, the last hop multicast router(s) may choose to
initiate a SPT switch-over at this point and the RP may end up being
taken out of the data plane).

So within the context of your scenario (or my understanding of it),
Anycast will provide the redundancy of RPs as well as the load balancing
depending on where your multicast receivers and senders are located in
respect to the RP's themselves. But having multiple RPs potentially
servicing the same multicast groups (i.e. Anycast) could cause a
disconnect between RPs and hence MSDP is required to ensure correct
operation.

Hope that helps.

Billy
On 05/01/2015 01:48 AM, Cisco Fanatic wrote:
> Experts, I am really confused as when to configure AnyCast and when to configure MSDP.
>
> I have this lab setup where I have two RPs configured. I have 4 routers statically configured with these two RP addresses. The clients behind the routers are receiving multicast stream.
>
> As I have configured RPs statically on the 4 routes, I do not have any form of load balancing and Redundancy of RPs. Correct?
>
> I was reading Cisco documentation where I am getting confused ..
>
> a) Do I only need to configure AnyCast for load balancing and Redundancy of RPs?
> b) Do I only need to configure MSDP for load balancing and Redundancy of RPs?
> c) Do I need to configure AnyCast + MSDP for load balancing and Redundancy of RPs?
>
> Not clear on the concept as when do we need AnyCast vs Anycast + MSDP?
>
> Hoping some smart gents and women can clear my doubt.
>
> -yuri
>
>
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Received on Mon May 04 2015 - 13:02:00 ART