RE: [pim] pim-sm DR, assertion and optimum traffic flow

["Ilya Varlashkin" <Ilya.Varlashkin at de.easynet.net>]

> -----Original Message-----
> Hi,
> 
> This would cause chaos in the network since it will make 
> pim-sm behavior quite unpredictable. You may visualise this 
> by considering CE11-FE2 disconnected to vlan-501 and thus 
> assert happening on Vlan-400 between
> CE11 and XR2 when CE2 requests packets from RP.
> 
Assert will never happen on VLAN400, because that's incoming interface
and what I've proposed is that router starts assert process only if
packet is _not_ on the incoming interface. Routers must never do assert
on the incoming interface (RPF interface), else they'll cut themselves
from the traffic (since traffic is allowed to arrive only RPF interface,
all other must be dropped). Moreover, if both routers are disconnected
from VLAN501, then there is no need for assert at all since there is no
longer need for the traffic.So no chaos here.

> If there exists a back door link (like in your topology) then 
> I feel that admin should configure a higher DR priority on 
> the router connected via backdoor link (viz. CE11) so that 
> probability of having sub-optimal path is minimized.
> 
The diagram I've provided is only trivial topology I could setup in
short time. Real network may exhibit significantly more complex case
where optimum path to RP is not fixed since RP itself can change (in
case of per group RP or due to failure of primary RP). In this case
there is no answer to 'who is better forwarder for the subnet' since it
depends on the topology at given moment of time and the source of the
traffic.

Regards,
iLya

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