[Xorp-users] open ports

[Pavlin Radoslavov]

> > Just curious, do you really mean IPv4 PIM-SM router, or is it IPv6?
> 
> It's IPv4 PIM-SM. 
>  
> > The reason I ask this is because currently NetBSD doesn't have PIM
> > kernel support for IPv4 (but only for IPv6). 
> 
> There are unintegrated PIM patches available, I'm running them.
> Moreover, xorp is running with igmp disabled and dr-priority = 0. Thus
> it never have to send encapsulated mulicast packets, the upstream and
> dowtream routers always handle that.
> 
> Is it possible that this configuration could work without the kernel PIM
> patches? It only have to exchange PIM packets with neightbors and
> install multicast routes.

If you are running PIM-SM as you describe above, and if you are not
the RP, then yes, you don't need the kernel support for PIM
Registers. In that case the only thing you need from the kernel is
to deliver to you the PIM control packets which I guess it can do
without any additional patches.

Hence, I would like to say that you can run PIM-SM without PIM
kernel patches, but myself I have never tried it and there could be
some surprises. For example, the *BSD kernels have a PIM-SM specific
bug regarding handing the delivery of the IGMPMSG_WRONGVIF upcalls
from the kernel to user-space (the signal is delivered only if the
network interface is broadcast capable). If you put this into the
PIM context, this means that if your NetBSD router is on the
cross-path between the source-specific tree and the shared tree, and
it uses p2p links, it may never complete the SPT switch: the SPT
data will be arriving to that router, but it will be dropped
there. Though, the downstream receivers will still be receiving the
data on the shared tree so you wouldn't observe any connectivity
problems; i.e., the only downside of this is the extra wasted bw on
the SPT that is not needed, and the fact that the data would be
arriving via the RP rather than the shortest path.

Another example that comes to mind is if some of your PIM-SM
neighbors on a LAN don't support the optional DR Priority Option. In
that case the dr-priority is not considered in the DR election,
hence your XORP router may still become the DR (if it has the
numerically largest IP address on the LAN). Hence, if that LAN has
senders, the XORP router running on non-modified kernel won't be
able to take care of transmitting the PIM Register packets.

Regards,
Pavlin