6500 Switch modify TTL of multicast source on the fly?

[MarkStites_2]

Hi,

I have an IGMP/multicast-routing enabled on a dozen VLANs on my 6509 switch. IGMP works beautifully. However, I have a couple very old machines which spray multicast with a TTL of 1 into their own VLAN.The receivers are on a seperate vlan and use IGMP. (the clients and sources were originally on the same VLAN) I cannot modify or rehost these customer owned boxes on newer platforms, or move them back on the same VLAN. With a TTL of 1, I cannot route across vlans when using multicast routing, coupled with IGMP management.

Any ACL's or techniques to modify the TTL on the way in, on a switchport? I do have the option of converting it to a routed port if ncessary.

Conversely, any way of routing multicast on a 100% IGMP enabled network to a box which cannot do IGMP?

I tried ip igmp join-group, it joins but the MC group, but it does not spray out the port toward the client as I had hoped... Am I using it wrong?

Thank you.

Mark

[Peter Paluch]

Hi Mark,

If your multicast application generates streams with TTL=1, there is no way of routing them into another VLAN. I haven't seen any option to mangle the TTL value in traversing packets on Cisco devices, neither. Sorry to disappoint you here.

Regarding the second question, the ip igmp join-group command makes the port to emit IGMP joins and thus to become something like a end host port (IGMP joins are generated in the opposite direction than the multicast traffic itself). Also, this command causes the multicasts to be received by the CPU of the device. This may not be what you want.

If you want to make some port an egress port for a multicast stream, use the ip igmp static-group command. This will "open" the port for the specified group and make it always flood the multicast stream out.

Best regards,

Peter

[MarkStites_2]

Hi Peter,

That's what I figured. I appreciate your help!

Just curious as the the use of the ip igmp-join command. When it sends the join message and MC flows toward the CPU of the receiving switch/router, what happens to the MC traffic? Does it just enter the multicast source table as a stream available for users to use IGMP and register for?

I'll check out the ip igmp static-group command! thanks!

Mark

[Peter Paluch]

Hi Mark,

In the case of the ip igmp join-group command, the MC traffic will be both processed by the CPU and flooded out through other ports (either in the same VLAN or routed to another VLANs accordingly - the usual rules for flooding and/or routing multicasts apply).

Best regards,

Peter