We build on our discussion from the previous blogs
The test topolgy
How R3 handles Server2 source multicast trafic?
R3 is the only UP router
It’s mroute table show a correct source and incoming interface but a Null outgoing interface list
The mrib shows
Similarily R3 mfib table shows that the incorming interface is accepting
But all packets are being dropped
No SW forwarding was into play
A debug on mfib shows that these packets were dropped because of no forwarding interface
Back to the mfib table
No SW forwarding
The “Other” counter indicates a total of 35 drops, 13 due to RPF
A debug ip pim shows nothing…
Let’s enable a downward PIM neighbor
PIMingly The neighbor is UP and added to the (*,226.0.0.1) which now in the forwarding state
A debug ip mrouting indicates that upon the reception of the trafic the mroute entry is created
Check the status of the mroute
We check the mfib table
The source is pruned and the “Other” counter is incrementing
From the beginning only 2 packets were SW forwarded
We clear mfib counters
Remark the NS flag for negate Signalling
Redo test
The flow is in mroute
R2 sends a prune request which supposes that it has received a multicast packet from the source
This is confirmed at R3 mfib
What “debug ip mfib pak” says?
We send exactly 3 packets from the source
First of all the signalling was needed to determine the outgoing intreface
Then TS (no idea!), FS (fast switching) and PS (process switching) accepted forwarding
The PS indicates no fowarding interfaces, dropping
The mfib table confirms that one packet were fowarded (FS)
The source stops
And the mfib at R3 is flagged with NS
Let’s now add a static igmp on R2 interface facing the receivers
At R3 the mroute shows a flagged T route and correctly populated incoming and outgoing lists
The mfib table has changed also
Now the incoming interface is marked A for accept
And the outgoing interface as F for forward
All packet were SW forwarded and no drops were registered
The debug shows the packet are being forwarded because the forwarding interface is known now
In dense mode PIM is not into much play
Routers on the path still signal its willingness to get the trafic or not (Prune)