[Xorp-hackers] RPF check in PIM-SM
bms at incunabulum.net
Mon Jul 27 07:43:14 PDT 2009
Chintan Shah wrote:
> We are trying to implement a fast repair mechanism for PIM-SM
> multicast trees.
> For that I need to know when is the RPF check performed on a received
> packet. From whatever I could gather,
> I understand that the kernel first tries to find a matching (S,G)
> entry in the MFC table and if it is found then it
> matches the incoming interface for the packet with the actual
> interface on which the packet was received and if both are same then
> forwards the packet to the outgoing interfaces from the outgoing
> interface list. My question is whether this is the only RPF check that
> is performed on the packet or is there any
> other check involved like looking up the unicast table and then
> checking the reverse path to the source
RPF checks normally happen in-kernel, and not under direct XORP control.
This is one reason why the fib2mrib process exists -- to push unicast
routes from the RIB into the MFEA.
> Could you please elaborate on how a multicast packet forwarded in the
> xorp router.
XORP doesn't forward packets, the host operating system does.
Both Linux and FreeBSD MROUTING have a common ancestor, they are pretty
much equivalent code.
Good luck with your app.
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