PIM More Info

Question 1

What is the high level difference between pim sparse mode and dense mode?

Answer 1

PIM dense mode is more ideal for instances where all subnets on the network have hosts receiving multicast traffic.

Question 2

How does PIM-SM ensure multicast group membership isn’t stale?

Answer 2

All membership states are timed out periodically, members must re-submit their join messages to stay joined.

Question 3

How does PIM dense mode use prune messages?

Answer 3

PIM dense mode sends multicast traffic to all PIM neighbours and relies on the neighbours sending prune messages for them to be marked as destinations not needing the traffic.

Question 4

Does sparse or dense mode use an RP or elected router?

Answer 4

Only sparse mode.

Question 5

How does sparse mode build a topology of routers who’ll receive traffic for a multicast address?

Answer 5

Each router must advertise to their neighbours that they want to receive particular multicast traffic?

Question 6

What is the PIM RPF check?

Answer 6

It’s a check to see if the source address and interface a PIM packet is received with is the same interface that the route to the source address would leave from. If it fails, it drops. This is to assist with a loop free design for routers in mesh scenarios.