[Xorp-users] Multicast Forwarding

[Pavlin Radoslavov]

> There is one hackish solution you could use with XORP, but it is a
> bit complicated:
> 
> 1. Configure the XORP box to be a static RP for the whole multicast
>    address range 224.0.0.0/4.
> 
> 2. Use the protocols/pimsm4/interface/vif/alternative-subnet
>    configuration statements on each Ethernet interface to add
>    entries to make all remote sources appear as directly connected
>    to one of the Ethernet interfaces.
>    You might have to be a little bit careful about the exact
>    configuration, because (a) you need to cover the address space
>    for all possible remote senders, and (b) if the multicast packets
>    from sender S1 appear on interface eth1, then eth1 must have
>    "alternative-subnet" configuration statement to cover the S1
>    address.
> 
> 3. The tricky part: Use PIM-SM (*,*,RP) Join on the Infiniband port.
>    As per the PIM-SM spec, the purpose of the (*,*,RP) Join is to
>    pull-down all multicast traffic that is routed in that RP.
>    Given that your XORP box will be the RP for all multicast groups,
>    as a result of that all traffic that reached any of the Ethernet
>    ports will be forwarded on the Infiniband port.
> 
>    The tricky part is how to get (*,*,RP) Join on the Infiniband
>    port. Those joins are suppose to be periodic and are suppose to
>    come from a PIM-SM neighbor. One option is to have a second
>    instance of XORP running on the TCA, but this is probably too
>    heavy for your requirements.
> 
>    If you have everything under your control, the more pragmatic
>    option is to modify the XORP source code to make it think that it
>    has received (*,*,RP) on the ib0 interface.

Forgot to mention that the cleaner option would be for us to add a
XORP configuration option to set the equivalent of (*,*,RP) Join
state per interface. I need to think more carefully what the exact
semantics should look like.
I remember in the past someone needed to do something unusual with
XORP which could be solved with a similar solution, so I think
adding such feature could be useful for various applications.

Again, please let me know whether you want to pursue this and we
could take it offline.

Regards,
Pavlin