Multicast and PortChannels

I am currently working a network that is using sparse mode. The network configuration is extremely simple…

Source PC > Router > Switch > Destination PC

My concern is the portchannel. All of the networks that are sending multicast traffic are in ospf area 0 while the port channel is in area 1. Should the portchannel be in the same area as the other networks?

Hello Shannon.

It all depends on what you want to do. Can you indicate where the Po interface exists on your topology? Can you also indicate the OSPF areas on your topology?



Thank you so much for your help! The Po channel exists on the router and is used to send vlan traffic. There are two connections (0/0 and 0/1) coming from the router to the switch. I figured the P0 was created to increase bandwidth since it is used for voice. My OSPF areas are 0 and 1. My networks are in area 0 and my P0 is in area 1.

Hello Shannon

OK, so back to your original question:

So your network is:

Source PC ------- Router ======== Switch --------- Destination PC

|_____ Area 0______|_______________ Area1_________________________|

And you have multicast traffic in OSPF area 0 and your concern is that multicast traffic from area 0 will not be flooded to adjacent OSPF areas. Well, according to this Cisco Documentation:

PIM is IP routing protocol-independent and can leverage whichever unicast routing protocols are used to populate the unicast routing table, including Enhanced Interior Gateway Routing Protocol (EIGRP), Open Shortest Path First (OSPF), Border Gateway Protocol (BGP), and static routes. PIM uses this unicast routing information to perform the multicast forwarding function. Although PIM is called a multicast routing protocol, it actually uses the unicast routing table to perform the RPF check function instead of building up a completely independent multicast routing table. Unlike other routing protocols, PIM does not send and receive routing updates between routers.

So essentially,PIM is independent of the routing protocol being used, and in the case of OSPF, is also independent of the OSPF areas created. This is the case for SM or DM as can be seen in the documentation further on…

I hope this has been helpful!