Problem: Routing multicast

Nazeem نجم لدين nazeemnss at
Sun Feb 14 09:36:41 UTC 2010


Thanks a lot, Werner.

The userspace multicast routing daemon (pimd) was exactly what I wanted. I
am able route multicast between pc2 and pc3 with it running.

I did not have a specific requirement of routing only multicast packets. So
normal routing table entries were enough.

Ya, this setup was related to my previous mail on VPN. This was to make a
way so that I need to make only one single tunnel between a server and
client using openvpn, and still be able to do ip-multicast between any
machines that were connected to the tunneling (the client and server of vpn
of each sides) machines using the common tunnel instead of each client
having a tunnel to server. This would make the whole vpn setup transparent
to the end machines and still be able to do ip-multicast.

I hope this is one of the "right" solutions. I would certainly like
suggestions if this is not one of the best ways.


On Sun, Feb 14, 2010 at 3:29 AM, Werner Schram <wrschram at> wrote:

> On Sat, Feb 13, 2010 at 12:26 PM, Nazeem نجم لدين <nazeemnss at>
> wrote:
> > hi,
> >
> > Consider 3 pc's,
> >
> > pc1: Has two 2 NIC's , eth0 ( and eth1 (
> > pc2: eth0 (, connected to eth0 of pc1 and has default gateway
> >
> > pc3: eth0 (, connected to eth1 of pc1 and has default gateway
> >
> >
> > ie,
> >  we have two subnets.
> >
> > [eth0] ---------- [eth0] |
> > [eth1]------------ [eth0]
> >        pc2                                               pc1
> >                               pc3
> >
> > Now how do I route multicast packets, so that I can ip-multicast from pc2
> to
> > pc3 or vice-versa?
> > The problem is that if trying to add route on pc 1, 224/4 has to be
> routed
> > to both eth0 and eth1 depending upon from whether they come from pc2 or
> pc3.
> I havent done to much with multicast, but maybe I can help you to get
> on your way. You noted that it is imposible to define a route in your
> routing table, which is correct. Multicast routing is a kind of
> anomally (in respect to common unicast traffic) which is handled by a
> userspace daemon on linux (take a look at pimd).
> The userspace daemon keeps track of the hosts that are subscribed to
> the multicast traffic, and routes the traffic accordingly.
> Subscriptions are handled using the IGMP protocol (so you should allow
> IGMP traffic in your firewalls and ACLs). If you have a host that
> sends multicast, it should route it to a host that can handle
> multicast subscriptions.
> So in your situation, you should run a multicast daemon on pc1 (pimd
> for example). I suspect this is related to the VPN setup from your
> earlier mail? If this is the case, do you only want multicast traffic
> to go trough the vpn, or all traffic? The first case might be a bit
> hard to setup so it might be easier to start with routing all traffic
> trough the VPN and then work to splitting off the normal traffic. To
> get multicast working, you should setup your hosts (pc2 and pc3) to
> route 224/4 to the server running the multicast daemon (pc1). You can
> do this by using static routes or by changing your dhcp configuration.
> If you route all traffic (so unicast and multicast) to pc1, you will
> have the default gateway set to pc1, in which case you shouldn't
> change anything.
> Note that errors are presented using the ICMP protocol, so if things
> don't work as expected, it might be a good idea to use wireshark or
> tcpdump to monitor those packets.
> This page has a pretty good explanation about what goes in in
> multicast (although section 2.3 doesn't explain the IGMP subscription
> mechanism, which I find slightly confusing):
> I hope this helps.
> Regards,
> Werner
> --
> ubuntu-users mailing list
> ubuntu-users at
> Modify settings or unsubscribe at:

لا اله الا الله محمد رسول الله
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <>

More information about the ubuntu-users mailing list