[Xorp-hackers] Problem in sending multicast traffic

[Bruce Simpson]

Chintan Shah wrote:
> ...
> Now when I start xorp on all routers and start the application on the 
> sender side, I get the following error message.
>
> setsockopt: IP_ADD_MEMBERSHIP : No such device
>
> I think there is no entry in the routing table and the traffic is sent 
> to the default interface and since that is not present , I get this error.
> I checked that the multicast routing and PIM-SM are enabled in the 
> kernel.  Also the interfaces
> support multicast.  I am not sure if it is alright to have the router 
> itself send and receive the multicast traffic with respect to IGMP 
> messages. 


    IP multicast applications need to be aware of the links available on 
the host system.  Unfortunately over time, IP multicast has been a 
generally misunderstood topic, and many applications do not support 
explicitly binding to an interface, although there have been many 
community resources explaining exactly why this is necessary, and how to 
achieve it.

    I believe VLC is not an offender here, however, it sounds as though 
the legacy multicast socket APIs are being used. Most multicast client 
implementations will choose the interface of the default gateway when no 
link is specified (either by IP address or interface index).

    You probably need to tell VLC to listen for multicast traffic on the 
IP address of B facing A.