From: John Galt Kupec (jkupec2@xxxxxxxxxx)
Date: Fri Feb 04 2000 - 01:03:15 GMT-3
Manjeet Chawla wrote:
>
> I am trying to understand the multicast groups and their application as
> could be applicable to lab scenarios. Here is scenario and the
> questions:
>
> ENET Serial Serial ENET ENET
> ---R1 -------CAT5k --------R2----|----R3 -----|
> | ENET
> R4
> |
> --- ENET
>
> If I am asked to implement multicast on this network and make sure all
> MCast groups can be pinged from all the routers, what would one be
> required to do ?
>
> Is it logical to put the same MC group on all the ENET (using ip igmp
> join command) ?
>
> What do I need to do on the CAT5k to enable cgmp/igmp. Any thing more
> than "set cgmp enable" ?
>
> I assume R1 and R2 interface into CAT5k should have "ip cgmp" ?
>
> Is there more to it ?
How are the R1 & R2 serial ports connected to the Cat5K?
You must enable multicast routing on all the routers that need to handle
multicast traffic. You must enable a multicast routing protocol on each
router interface that will handle multicast traffic. However, not every
router interface necessarily needs to "join" a multicast group.
On each router that should handle multicast traffic:
Enable "ip multicast-routing", and then for each interface that will be
involved in multicast routing you have to enable a multicast routing
protocol. PIM is probably your best bet here.
You would configure "ip pim dense-mode", "ip pim sparse-mode", or
"ip pim sparse-dense-mode" on the interfaces. "Sparse" PIM requires
a Rendezvous Point (RP). For the topology you describe above I would
just configure dense-mode or sparse-dense-mode PIM. If there's no
RP, then the sparse-dense-mode _should_ assume a "dense" mcast network.
For lab purposes, you would use "ip igmp join-group <multicast-group>"
on an interface in order to test. This command makes the router
interface itself join a multicast group.
Assuming you have multicast routing enabled and PIM properly configured,
you could do the following on R4 & R3 Ethernet interfaces (say the
furthest ones from R1)
int e <#>
ip igmp join-group 239.0.0.0
and then from R1 you could "ping 239.0.0.0" and you should see
packets echo back from both R3 & R4.
I _don't_ think it's technically necessary to configure CGMP on the
router ports connected to the Cat5K- by default, shouldn't multicast
traffic be treated as broadcast traffic and be forwarded out every Cat
port? The CGMP protocol allows you to be selective about where the
multicast traffic should go (selected ports, not all ports). CGMP is
a GOOD THING, but I _believe_ you could omit the CGMP configurations
and still have it work- Anyone? Anyone? Ferris?
All that being said, you should probably just configure CGMP on each
router port connected to the Cat5K and be done with it...
Hope this is a help and not a hindrance. Corrections/comments welcome.
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