Anycast RP and Multicast.

[omarmontes]

Hi guys, let me explain you my situation:

I'm trying to implement Anycast RP on my Multicast network so I can use more than one RP. I've already read the documentation about it, and I understand that the same IP address must be configured on a loopback interface on all the RPs. Also, this same address must be statically configured on every other non RP router.

The question is: what IP address should I use? does it have to be from one of the subnets that the router advertise? What if the other RPs don't have that particular subnet? How is it going to advertise it?

I guess the 2 RPs must be directly connected and then I can use an IP address of the subnet used by the point to point link.(using a /29 instead of a /30).

Thanks in advance!

[smif101]

I created a paper on configuring multicast on my website, here is the link and maybe it will help you out.

http://www.smif101.com/Cisco/Configuring%20Multicast.htm

[omarmontes]

Thanks for the link, the security configuration and unix guide is great.

Unfortunatelly, I couldnt get the information I need from your Multicast guide, so the question's still open.

[Harold Ritter]

Tipically you would configure two loopback interfaces, the first one with an IP address that will be common to all the RPs (anycast address) and the second one with a unique IP address. Here's a good example of how to configure IP addresses for anycast RP:

http://www.cisco.com/en/US/partner/tech/tk828/tk363/technologies_white_paper09186a00800d6b60.shtml#57583

Hope this helps,

[omarmontes]

Thanks for the link hritter, thats the document I've read, but it doesn't mention if the RPs need to be together or how to deal with the anycast IP address. I don't know if im explaining it well, but the question here is: can the RPs be some hops away?, and what IP address should I use, in order to be advertised by the routing protocol (so the election of the closest RP by the non RPs can be done).

If I use an IP that belongs to one of the subnets configured on the router, then there is no problem, its going to be advertised as usual. But if another RP, with the same anycast IP is configured, but the router doesn't have the same subnet, how is the IP address going to be advertised? Do I have to make the routing protocol advertise that subnet? how is it going to interfere with normal traffic to that subnet?

[Harold Ritter]

The RPs can be side by side or they can be many hops away. You mainly need to advertise the anycast address (the same address assigned to all the RPs).This way if a non-rp router is closer to RPx, it will go to RPx and if another non-rp router is closer to RPy it will go to RPy. But bear in mind that the RP address specified on the non-rp address will be the same.

You should never use a physical interface as the anycast address. You should always use a loopback interface IP address and advertise in your IGP.

Hope this helps,

[omarmontes]

Ohh I see, thank you hritter!

Just one more thing, I assume that the routing protocol will anounce just that IP address (the anycast address) and not the whole subnet, right? otherwise it would cause a conflict with the router that does have the subnet.

Sorry for the trouble :)

[Harold Ritter · Accepted solution]

It is more efficient to configure a /32 (host route) for that loopback interface IP address since all you need is one address. It wouldn't cause a problem per se to configure and advertise it as a /24 but it wouldn't be very efficient.

Hope this helps,

[omarmontes]

Thank you hritter, I think the problem is solved :)