Basic Multicasting with multiple Cisco switches
Posted on 2012-09-17
I'm trying to wrap my mind around Multicasting. I really have searched, but I'm stuck at what is probably a basic understanding issue. Never the less, I'm at your mercy.
I understand the reason for Multicasting. It saves bandwidth on what would otherwise be a bundle of unicast traffic. I have the simple understanding (in my mind) that Multicasting is basically a unicast transmission, but to the broadcast address of a subnet so multiple devices can receive the data at once. Then I also understand it can also be routed across layer 3 (but I'm foggy on how). So enough jabber...
Where I get confused is in the Cisco protocols and why to use one over another. Then the implementation.
I have a handful of 3550s (running IPSERVICES) each handling their own multiple VLANs in their respective sites. IP Routing is done through these same switches. They are linked via TLS 6mbps (WAN) through our ISP.
Each 3550 I've done the following:
"ip multicast-routing directed" applied.
Each VLAN to allow multicast has
"ip pim dense" applied.
So far that is the extent of the configuration. The goal is to reduce the amount of multicast bandwidth as much as possible The source of the multicast will be located in only one site. I plan on the multicast having to span the WAN links (maybe this is a dumb idea) to service the other sites.
The source is intended to be a multicast live stream coming from a VLC server. In the VLC software I'm able to "stream to an IP". I'm guessing this would be a multicast IP. A single unicast stream is roughly 500-700kbps depending on quality.
So with that background:
- First am I dumb for Multicasting across WAN links?
- Is PIM dense the best option, or is sparse better? Or maybe IGMP? Why?
- Do I need to have any other config for the switches to route the multicast to multiple VLANs? Including across my WAN links?
- With regards to the VLC software wanting to "multicast to an IP", where is that IP? Do I make it up? Do I need to assign it virtually to a switch interface?
Let's start here and see where this goes.