All things related to multicast

[Leonard Giuliano <>]

So you are saying that you have transit LANs in your backbone and you
don't want mcast traffic flooded out all ports?  If so, using VLANs as
you suggested is one way to do this.  This has the benefits of creating a
logical p2p topology, which greatly simplifies mcast behavior (no asserts,
no flooding, etc).  The disadvantage is that you may end up consuming more
bandwidth as you replicate the same packets down different logical
interfaces on the same physical interface.  So if fannout is high, you get
inefficient replication.

Regarding the routing piece, are you saying that you only want mcast to
use these p2p VLANs, while unicast uses the the broadcast LANs?  If so,
this is what MISIS does.  MISIS is to IGPs what MBGP is to your EGP.  So
if you want to have an incongruent topology WITHIN your domain, MISIS is
an ideal choice.  Unfortunately, MISIS is not implemented by all router
vendors, so that may not be a choice for you.  MBGP can be used, but it
gets real messy, as you end up trying to make MBGP behave like an IGP.
Of course, if incongruence BETWEEN domains is what you want, MBGP is
ideal.

The better question may be why do you want incongruence in the first
place?  If you are going through the trouble of creating these p2p VLANs,
why not let unicast use them?  You might be better off creating this
topology and letting unicast and mcast flow congruently through it.


Hope this helps,
Lenny

On Tue, 19 Aug 2003, [iso-8859-1] Luís Marta wrote:

-) Hi.
-)
-) If one has a backbone network based on Fast/Gigabit Ethernet, different
-) brands of routers and not-so-powerful switches (no chance of running RGMP),
-) how does one implement multicast?
-) In order to avoid the multicast traffic to leak to all the switches' ports,
-) i thought of creating a separate VLAN to the multicast traffic, a VLAN that
-) connects the RP, the backbone routers until the last one before the client
-) (the access routers), but then the last connection may be ATM ou any other
-) technology.
-) As PIM interacts with the routing protocol in use (OSPF for example), how
-) can i make the multicast traffic that is supposed to go to a certain client
-) use the mentioned VLAN? Is there any other way of doing this without using
-) static mroutes to map the clients' routes? Because this is very
-) time-consuming and impossible to maintain.
-)
-) Thanks in advance,
-)
-) Luís Marta.
-)