multicast

Unanswered Question
Sep 6th, 2007

Hi I have tried to read the cisco docs this but it is not as clear as it should be. What exactly is needed to implement this acros the network ? Turn on multicast routing , set pim on interfaces? Does the pim statements go on all interfaces or just on connecting interfaces between layer 3 switches ? What else is needed to implement this across a fairly good size network ? Any help and config tips appreciated .

I have this problem too.
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Joseph W. Doherty Thu, 09/06/2007 - 19:42

If you're trying to understand multicast, especially "to implement this across a fairly good size network", a first good tip might be to obtain a couple of good tutorial books on the subject. Cisco Press likely has some. Good design and configuration of multicast can be complex.

"What exactly is needed to implement this acros the network ?"

If your networks comprises routers, and you want multicast to transit them, then multicast capable routers.

"Turn on multicast routing , set pim on interfaces?"

Usually need to enable multicast routing. If using PIM on Cisco routers, it's configured on interfaces.

"Does the pim statements go on all interfaces or just on connecting interfaces between layer 3 switches ?"

On Cisco routers, believe you need PIM enabled on all interfaces that are to process multicast traffic, even leaves.

"What else is needed to implement this across a fairly good size network ?"

A good design. Equipment that handles multicast well and with advanced multicast features is a major plus for good sized networks.

glen.grant Sat, 09/08/2007 - 08:18

What has to be done on WAN routers ? Is it as simple as putting pim statements on the wan facing interfaces and turning on multicast routing on each end or are their additional steps that need to be done ? I know there has to be some thought put into this specially where you have limited bandwidth links .

Richard Burts Sat, 09/08/2007 - 09:13

Glen

I believe that the answer to your question will depend on what you decide about the PIM mode that you will use: will it be dense, sparse, or sparse/dense? If you choose dense mode then I believe it is about as simple as enabling multicast routing and putting PIM statements on the interfaces that will carry multicast. (But I believe that some people would say that dense mode is a suboptimal choice for WAN interfaces) If you choose sparse or sparse/dense then you have to work out which router will be the RP and how routers will learn the RP. There are several options and this will add some statements to your config.

HTH

Rick

Edison Ortiz Sat, 09/08/2007 - 12:05

Glen,

Multicast is one of those protocols when you need a good network diagram for implementation.

If you post a diagram, we can give you a better recommendation on what interfaces to enable PIM, the PIM mode to use and if you need a RP.

Also, please tell us where you are placing the Multicast Source (also known as the server) and where the Multicast Receivers will be (also known as the clients).

Joseph W. Doherty Sat, 09/08/2007 - 12:29

As Rick notes, if you're using DM-PIM, you don't need to do much more than just add the PIM DM statement to the interface. You would also need to enable PIM on more than just the WAN interface, LAN side too. If there are other routers along the path from source to destination, they too will need PIM activated on their interfaces.

Although DM PIM is one of the easiest to configure, it's a "flood and prune" protocol, which is why Rick notes SM PIM is often preferred for WAN links.

If I remember correctly, the only other requirement for PIM to work correctly across multiple routers is the routers will need routes for PIM to use, such as would be provided by a routing protocol, e.g EIGRP or OSPF, etc.

PS:

One issue that often arises when doing multicast is whether you want all hosts to see the stream, usually addressed by switches that support IGMP snooping, or all routers to see a stream on a shared subnet, which can be addressed by PIM snooping (if using PIM).

Another issue that can arise if you use mixed vendor equipment, or even Cisco equipment of different vintages. The former might only want to support something like DVMRP or not support all the same PIM protocols as the Cisco equipment, the latter may also not support all the same multicast features.

glen.grant Sat, 09/08/2007 - 16:07

Thanks for everyones reply , I realize that all connecting interfaces have to have pim enabled , I was just wondering about the WAN links and how they are handled . I read somewhere that your best option is to use sparse-dense mode with igmp snooping on your access switches . Using sparse mode kind of looks like a pain then you have to get into configuring rendevous points etc... This is a lot of configuring if you are talking about implementing this across a decent

size network . Have to do some more reading .. :-)

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