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Michael McCabeFlag for United States of America

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Basic Multicasting with multiple Cisco switches

Hello Experts,
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.

Thanks
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Wow, excellent job... That's dead on what I needed to hear.  

The Pim-SM in reading did say that it has the ability to be less resource intensive.  I'll read more about it, but at the same time implementing was also stated as being more difficult.

When speaking about Pim-DM or Pim-SM, how are clients (receivers of the multicast) able to jump on the multicast and then off?  For example in my scenario my stream from the VLC server will be started at 9am.  Let's say I have some late comers who don't sign onto the multicast until 9:30am and then more at 10am.  

If Pim-DM initially blows out through the network to fill its tables, how do the late-comers gain access?  Or is it filling a table with regards to just subnets?

(edit - maybe I actually don't need to know the "how..." as much as an answer of "Just know that it works that way..." would satisfy.)

All Layer 3 hops (routers or L3 switches) between your LANs must be PIM enabled.  If you have a L3 service from your WAN provider, they will need to support multicast, or your will need to tunnel it.
No my ISP just carries Layer 2.
Just to confirm, this is one example on the switch.  Is this all the configuration necessary if I was to run Pim-DM?       Seems pretty simple...  almost too simple...

Global:
ip multicast-routing distributed

Open in new window

Interfaces:
interface Vlan230
 description Comp_Labs
 ip address 10.1.230.1 255.255.255.0
 ip helper-address 10.48.64.4
 ip pim dense-mode

Open in new window


As far as the IGMP snooping goes and applying it to the interfaces, it appears that it is enabled by default.  I'm not sure if there is anything extra to do with it in the configs.
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You Rock!  
Couldn't have been easier to read.  While I completely agree with additional reads, you've given a great synopsis.  This'll definately get me rolling and will help many others.  Thanks!