Multicast helper clarification

From: dan.bliss@gmail.com
Date: Tue Oct 17 2006 - 00:45:38 ART


All,

Ok, I have searched the archives and did not find a "definitive" answer for the following questions and would appreciate your assistance:

Where do we "NEED" the "ip directed-broadcast" statements when using multicast helper? And does it matter if the source is a subnet only broadcast or all hosts broadcast? The cisco documentation is very vague and even just plain wrong in parts.

(some of the following is copied from an archived post, i just modified it to save time)

So this is my understanding so far:

               

       | ( ) |
source |--R1--( Mcast )--R2--| Destination
       | ^ (_____) ^ ^ |
         1 2 3

------------------------------------------------------
The following configuration should go on interface "1"

ip multicast helper-map broadcast 225.5.5.5 100

(where 255.5.5.5 is the multicast address to convert the broadcast to and
"100" is an extended access-list that matches the traffic to convert.)

The following configuration should go on interface "2"

ip multicast helper-map 225.5.5.5 12.255.255.255 100

(where 255.5.5.5 is the same group as previously referenced, 12.255.255.255
is the directed broadcast address of interface "3", and access-list 100 is
the same as previously referenced)

Globally we need an acl to match the traffic on R1 and R2
access-list 100 permit udp any any eq 4000

Globally we need the router to perform the conversion at the process level on R1 and R2
ip forward-protocol udp 4000
------------------------------------------------------------------------

So, where does the ip directed-broadcast statement(s) go? Cisco says point 1 and point 3, are they correct?

I have seen it work with it applied only at point 3 in the diagram only which makes the most sense to me.

Thanks in advance,

Dan Bliss

P.S. Thanks to Pierre-Alex for answering my last multicast question. Much appreciated.



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