[KLUG Members] Packet routeing

[Adam Williams]

> Ok. Here is a weird request I got from the higher ups regarding another 
> project.  One project is using UDP multicast to pass around data from 
> several programs on several machines on a local net using a multicast 
> group.  This program apparently needs to no which computer sent the data, 
> so it looks at the source address of the UDP packet.
> Now they would like to do the same thing, but with programs located on two 
> subnets which are in different states.
> How can I bridge the gap? My only experience with multicast is to get 
> programs chatting on a local subnet. I think the requirement to keep the 
> source address of the packet might cause problems.
> This is a many server to many client situation, like a peer-to-peer 
> multicast group.
> is this as simple as turning on PIM-DM on the routers on both subnets and 
> in between?

I believe that should work (or a similair feature, it has been awhile
since I read the Cisco manuals).....

Ok, assumming an English accent so I sound more intelligent, and blowing
the dust of these huge tomes....

Hmmm, there is nothing about multicast in "Cisco IOS Configuration
Fundamentals". :(  It doesn't even appear in the index.  Also nothing in
"Routing TCP/IP Vol I".  There is a section on Multicast with
frame-relay using map commands in "Cisco TCP/IP" but you said your using
leased lines.

"Internetworking Troubleshooting Handbook" has a section on IP Multicast
and it supports your enable PIM-DM theory (Protocol Independed Multicast
- Dense Mode).

Ufortunately there seems to be alot of focus on multi-cast in relation
to routing protocol and not so much on application level multicast.

I'm curious to know how your solution works out.  My understanding on
multi-cast is at the "hubble bubble toil & trouble" stage and I haven't
had the opportunity to work with any apps that use it.  When we bought
them I was expecting our 13 VOIP phone systems to multicast status
information, but they just use an "extended" version of ICMP.

Perhaps there is a CNE out there that would be willing to explain to
KLUG the inner-workings of multi-cast?