[Xorp-users] multicast problem (solved)

Felix Engel felix.engel@beanpower.de
Sat, 12 Mar 2005 12:17:42 +0100


On Thursday 10 March 2005 00:55, you wrote:
> > > Also, did the receiver get the multicast traffic?
> >
> > no. in both directions the same. i can send but the receiver is getting
> > no traffic. i also tried another gentoo box with the latest cvs-version
> > of xorp. and another multicast-application. but the same result.
>
> This is odd. In your first email, you sent the following info:
>
> cat /proc/net/ip_mr_cache
> Group    Origin   Iif     Pkts    Bytes    Wrong Oifs
> 0A0100E0 024D4237 1      94007 126345408        0  0:1
>
> In other words, your kernel has the correct MFC entry for source
> 55.66.77.2 and group 224.0.1.10, the iif is eth1, and the oif is
> eth0 (with min ttl of 1 needed to forward a packet). Furthermore,
> the kernel has seen 94007 packets that match on that entry (and that
> are eventually forwarded, unless the ttl is not large enough).
>
> Three issues come to mind:
>
>  * The TTL of the data packets is not large enough. You mentioned in
>    your first email that it is large enough, but just double-check
>    it by running tcpdump on both eth0 and eth1. Running
>    tcpdump will also show you if the multicast packets are indeed
>    forwarded out on eth0.
the problem was the ttl. there is a problem in the vlc-streaming-gui i think. 
you can define the ttl, but it is not used. vlc uses only the default ttl=1. 
the solution was to run vlc in text-mode wih --ttl option.

thank you very much for your help.

felix
>
>  * If the receiver is on the same host as the multicast router,
>    there could be some kernel issues with delivering the multicast
>    data packets to local receivers. I vaguely remember that there
>    were some issues with local multicast receivers running on the
>    same machine as the multicast router, but I don't have the notes
>    with me to check the details (OS, setup, etc).
>    To make sure this doesn't affect you, have your sender and
>    receiver running on hosts directly connected to your multicast
>    router.
>
>  * You may have some filters in your kernel (firewall rules, etc)
>    which are stopping the multicast traffic.
>    At least, make sure that the "rp_filter" in the Linux kernel
>    is reset to 0:
>    cat /proc/sys/net/ipv4/conf/all/rp_filter
>    echo 0 > /proc/sys/net/ipv4/conf/all/rp_filter
>
>
> Regards,
> Pavlin

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 e-mail: felix.engel@beanpower.de