Rebroadcast Multicast possible?

markstites · ‎03-02-2009

Hi,

I have a 6509, SUP 720. Latest IOS.

Two VLANS: 10 and 20.

10.10.10.254 is the vlan 10 interface.

192.168.1.254 is the vlan 20 interface.

I have a user shooting multicast with a TTL of 1 into vlan 10. Unfortunately the TTL is hardcoded into this custom application and is unchangeable.

I need a way of routing this traffic into VLAN20 via IGMP/MC routing. There is the possibility that there will be future routers/switches hanging off of vlan 20 whom may have users who want this multicast.

I've read Google'd like crazy and read Cisco's docs on multicast regarding thresholds, IGMP snooping etc..I've experimented but to no avail. I tried an "ip igmp join ..." on vlan 20, it joins but my hosts still cannot IGMP request the stream.

Am I up the creek without a paddle?

thanks for any help,

Mark

Harold Ritter · ‎03-02-2009

Mark,

Unfortunately, I can't think of any easy way to do that.

If it is just these two VLANs, you could attach the multicast server to both VLANs.

Regards

Harold Ritter
Sr Technical Leader
CCIE 4168 (R&S, SP)
harold@cisco.com
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markstites · ‎03-02-2009

Thank you, that's what I thought!

Joseph W. Doherty · ‎02-22-2023

. . . w/o a paddle?

On a Cisco switch or router, very likely.

Perhaps easiest solution would be an app on a PC to accept multicast and retransmit it with a greater TTL.

Another approach might be bridge those two VLANs and block all but multicast.

pieterh · ‎02-23-2023

is'nt is by design that multicasts have a TTL of 1 ?
this is enough to reach the first-hop router that functions as a RP (rendez-vouz point for multicastst)
this router distributes the multicastst again with a TTL of 1 to reach a next RP or a client
-> check the configuration of your router that is acts as an RP for this multicast group

Joseph W. Doherty · ‎02-23-2023

Re: Multicast by design have TTL of 1?

No.

In usage, multicast intended for local L2 broadcast domain should have a TTL of 1.

(You might also want to review Cisco's TechNote, discussing OP's problem, and fix [i.e. have multicast sender increased TTL].)

BTW, you might misunderstand what's a RP.

PS:

Https://stackoverflow.com/questions/447500/how-can-i-modify-multicast