Basic PIM-SM w/ Autorp

Unanswered Question
Jan 14th, 2008

All,

I'm setting up a basic PIM-SM w/ Autorp to provide multicast to a new WAN connection. The RPs are two 4500s that act as the L3 core of the network. They have a few multicast sources directly connected to L3 interfaces.

I have a new 7206 router that has an Ethernet connection to each 4500 routing via OSPF. This 7200 will be the new WAN router for the environment and the first and only use of multicast across the WAN.

I have used the basic config posted here. The 7206 does not show the RP information <blank for show ip pim rp> or the multicast groups in the mroute table except for the expected 224.0.1.39,224.0.1.40. The 4500s show all expected mroutes and sources.

Any help is appreciated. I can post more config or outputs of show commands as necessary.

7206

=======

ip multicast-routing

int lo0

ip pim sparse-mode

int g0/1 ! To 4500A

ip address x.x.x.x

ip pim sparse-mode

int g0/2 ! to 4500B

ip address x.x.x.x

ip pim sparse-mode

ip pim autorp listener

4500A

============

ip multicast-routing

int lo0

ip address x.x.x.x

ip pim sparse-mode

int vl10 !to 7206

ip address x.x.x.x

ip pim sparse-mode

ip pim autorp listener

ip pim send-rp-announce Loopback0 scope 8

ip pim send-rp-discovery Loopback0 scope 8

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Jon Marshall Mon, 01/14/2008 - 18:13

Hi Shannon

If there are no receivers actively requesting a multicast stream then this is normal. So it doesn't mean it's not working it just means that no host has registered an interest with IGMP.

224.0.1.39 & 224.0.1.40 will not show up in a "sh ip pim rp".

Once a host on the other side of the 7200 requests one of the multicast streams then you should see entries for that group on the 7200.

HTH

Jon

shannong Tue, 01/15/2008 - 05:54

Thanks. The addtional info was very helpful. We'll be testing the first site tonight and I'll let you know the results.

Kevin Dorrell Tue, 01/15/2008 - 06:26

Shannon,

I am no expert in multicast, but I think if you are using auto-rp and your 4500A is the RP, then you might need ip pim sparse-dense-mode on the interface facing the 7206. Otherwise the 7206 may not hear the RP announcements because they are carried on a group that is itself subject to sparse-mode joining rules.

Alternatively, with so few routers you could configure the RP statically on each one.

Kevin Dorrell

Luxembourg

Jon Marshall Tue, 01/15/2008 - 06:32

Hi Kevin

As far as i know you can use 2 ways to enable autorp

1) As you say - configure "ip pim sparse-dense-mode" under the interface

2) Configure "ip pim sparse-mode" under the interface and "ip pim autorp listener" in global config.

Shannon is using the 2nd one by the looks of it.

Jon

Kevin Dorrell Tue, 01/15/2008 - 07:57

OK, I just learned something new and useful. I guess what it does is to generate PIM joins for the group that carries the autorp. Which has got to be more efficient than sparse-dense-mode which opens it up for any group that doesn't have an RP yet.

Would he need that on the non-RP end of the link then, i.e. on the 7200? If I understand you right, ip pim autorp listener pulls the autorp announcements from the RP, whereas sparse-dense-mode floods it out from the RP.

Kevin Dorrell

Luxembourg

Jon Marshall Tue, 01/15/2008 - 23:50

Kevin

"ip pim autorp listener" causes IP multicast traffic for 224.0.1.39 & 224.0.1.40 to be dense mode flooded out of all interfaces running in pim sparse mode.

So it is only actually needed on the RP itself although it actually doesn't seem to do any harm in my lab when you enable it on the non-RP devices.

Jon

Kevin Dorrell Wed, 01/16/2008 - 00:51

Thanks Jon. They didn't choose a very good name for it, did they! I would have expected the ip pim autorp listener to be on the router that is listening for the RP announcements, not the one that is pushing them out.

This also means, presumably, that if you have receivers that are two or more hops away, then you need to configure ip pim autorp listener on each hop in order to get the announcement flooded down the tree. Everywhere, that is, except on the leaf nodes, where it is benign but unnecessary.

I have a day off for lab work today, so I'll add it to my list.

Kevin Dorrell

Luxembourg

Jon Marshall Wed, 01/16/2008 - 01:36

Kevin

Yes i agree, it does seem like the wrong name which always makes me suspicious :) I'm going to run a few more tests and i'll let you know what i find out.

Jon

shannong Tue, 01/15/2008 - 06:38

Thanks, Kevin. Previously, it was as you describe. It is my understanding that the "autorp listener" command alleviates the need for sparse-dense mode. While the interface may only send in Sparse mode, it will also accept dense mode messages for AutoRP. Of course the RPs themselves will be sending the messages due to the configuration of the "send-rp" commands.

The brief explanation only included 3 routers, but there will be approx. 40 sites connecting to this new 7206.

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