All things related to multicast

["Marshall Eubanks" <>]

On Mon, 24 Jan 2005 11:20:37 -0500
 Jay Young 
<>
 wrote:
> One of our groups on campus is using a real media server to stream media 
> across campus, they have it setup to use multicast as well. They are 
> wanting to setup a load balancer in front of multiple servers.
> 
> Does anyone have any experience using a load balancer in front of 
> multicast sources? Products to look into / stay away from?
> 

I am not sure this is a well posed question.

I believe that the kind of load balencing you are talking about is when 
requests for new
services (web or streaming) are divided among several servers. Multicast 
doesn't in general work
that way. Generally, multicast streams are sent out full time (for the 
duration of the stream, which
can be "infinite"). So, in a sense, there is only static load balancing (if 
you want to have certain
multicast streams coming from box A, others from box B, you just set it up 
that way).

What would be useful is multicast failover - I am not aware of a good 
solution there, and I could
use one. (I.e., if box A dies, box B starts sourcing A's streams). In the 
anycase streaming or web
case, this is something that you may get "for free" from the load balancer 
(in that the next request
for service will only go to a live box), but not for multicast (because the 
source never gets
requests).

Now, there is also load balancing for bandwidth. Suppose you have multiple 
pipes to the same
upstream provider. Multicast only knows one true path, and so all multicast 
will go out only one
pipe. To really get any sort of bandwidth load balancing in this case you 
have to bond the pipes
together, using something like PPP Multilink, to get any benefit.

If the multiple pipes are to different providers, you basically
can't do any bandwidth load balancing at all.
In the unicast case you can set up BGP so that part of the internet goes 
through provider A, part
through provider B, but this doesn't work for multicast - you'll just 
guarantee that a copy of the
multicast stream goes out of each external interface if there are receivers 
in both parts.

Of course, given the limited deployment of multicast, what a lot of people do 
is have
one pipe to the multicast enabled Internet 2, other pipes to non-multicast 
enabled providers, which
is a sort of load balancing, but probably not what you are interested in.

Regards
Marshall

Regards
Marshall Eubanks



> Thanks,
> Jay
> 
> -- 
> Jay Young                     |Office of Information Technology
> Network Engineer              |The Ohio State University
> Phone: (614) 292-7350         |320 West 8th
> Fax:   (614) 292-9525         |Columbus, OH 43201