Rerouting messages

[UnixL]

Let's say I have messages going from A, B, C to D and I want D to route those messages to computer E (using multicast). Am I going to need an application like Quagga (can't post the link) to do something like this for me, or can i use something as simple as routing tables that are built into linux on computer D?

[Irithori]

Messages are packets I assume?

If E shall not answer but only receive packets, then probably a mirror/monitor port is a possibilty here if your switch supports it:
Catalyst Switched Port Analyzer (SPAN) Configuration Example - Cisco Systems

[UnixL]

Yes, packets. I believe I just need to change PREROUTING somewhere in my settings. I've been playing around with this so long this week I can't believe I just found out about it.

[UnixL]

I hope you guys don't mind if I voice what I'm doing right now.

I have computer A which sends packets to computer B. For security purposes I'm going to say it sends multicast packets to all that subscribe to 231.1.1.1.
Computer B receives the messages into ip address 192.168.1.2.
I have the rule: iptables -t nat -A PREROUTING -i em0(192.168.1.2) -j DNAT --to 232.1.1.1
the part in parentheses is not written, and i have changed the ip addresses.
Computer C is subscribing to 232.1.1.1, but only receives pings to 232.1.1.1 from Computer B. It will not receive the packets that A multicasts to.
Something tells me that the multicast packets going into Computer B does not get noticed by iptables. Any ideas if I'm on to something or not?