IPv4 Multicast

Jamie Sobczyk lanson9 at cox.net
Fri May 21 14:52:02 UTC 2010

Make sure you have
"ip multicast-routing"
on both routers.

On the router interfaces, make sure you have
"ip pim sparse-mode"

On both routers, make sure you have the same rp address assigned and 
that you can ping this ip address from both routers. (I prefer to make 
it a loopback interface)
"ip pim rp-address w.x.y.z"

Also, make sure that routing is setup on your routers so that your 
receiver can ping your sender.

On your routers you should be able to see the source unicast address and 
multicast address by typing "show ip mroute"
you should see something like this:
(*,, 7w0d/00:02:59, RP, flags: S
   Incoming interface: Null, RPF nbr
   Outgoing interface list:
     Port-channel15, Forward/Sparse, 7w0d/00:02:59, H

(,, 4w5d/00:03:27, flags: TA
   Incoming interface: Port-channel15, RPF nbr
   Outgoing interface list:
     Port-channel17, Forward/Sparse, 4w5d/00:02:49, H

On your switches, with igmp snooping enabled, you should be able to 
"show ip igmp snooping group" and see something like
Vlan      Group                    Type        Version     Port List
24             igmp        v2          Gi1/0/21
That port listed is the port of the requester.

-----Original Message-----
I have setup a lab for this multicast.

VLC receiver - 3560G - 1841 - 1841 - 4503 - VLC sender

The 2 switches only provide L2 access, they have IGMP snooping active

On both 1841's I have pim parse-mode & sap listen on all interfaces +
configured a static RP, the one closest to the sender.

With my VLC receiver I can see the channels via SAP, but when I join the
multicast group I don't receive anything.

Could someone help me to troubleshoot this?

Thanks in advance,


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