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Author Topic: Question on ipv6 multicast  (Read 2714 times)

dcottle

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Question on ipv6 multicast
« on: January 13, 2011, 03:53:20 PM »

I have two nics, eth1 is WAN, eth2 is LAN

All my ipv6 is working with radvd all clients, etc.

My question is multicast.

With ipv4 I had to make a /etc/sysconfig/network-scripts/route-eth2
224.0.0.0/4 via 192.168.0.1

What do I need to add here to get multicast ipv6 running?

Also let me know if the above is wrong, I was told Linux you can only multicast to one NIC, it has to be your internal LAN one.

Someone also suggested using 224.0.0.0/4 via eth2 but this does not seem right?

Thanks again!

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jimb

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Re: Question on ipv6 multicast
« Reply #1 on: January 14, 2011, 06:22:33 PM »

hrm.  Someone correct me if I'm wrong, but I've never heard of needing to set a static route for the whole multicast space.  I see a multcast address not really as an address but more of a "channel" that nodes can tune into or ignore.

Multicast on a LAN usually works via IGMP, etc.  Then you can set your switches for IGMP snooping so it doesn't spam every port, etc.  For IPv6 you'd use MLD snoopng, since it uses MLD instead of IGMP.

In more complex networks you also run a MC routing proto like PIM, or whatever the latest thing is.
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SjH

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Re: Question on ipv6 multicast
« Reply #2 on: February 21, 2011, 06:31:07 AM »

Indeed. Multicast "routing" is a different kettle of fish to the routing that you would see for unicast traffic.

Link local multicast is essentially fire and forget - your computer joins the multicast group, and can listen or send traffic to all other nodes listening on that group (for example ICMP packets used in IPv6 ND requests). However when you increase the scope, you require a multicast router and a Rendez-vous point (RP). Basically your computer sends out an IGMP for v4 or MLD packet (v6) onto the link saying that I want to join the multicast group. It then in turn joins the group and forwards traffic onto that LAN which you can here (as it is multicast traffic). Its a bit more complicated than this, but as a quick intro its not too bad. There are plenty of PP or PDFs out there that go into the details in great detail, so I'll leave it there.
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