Multicast DR and First Hop Router and DR

dppagc

I have questions about Multicast DR & "First Hop Router".

Correct me if I am wrong:

The DR is between the receiver and RP on the same segment.

The first hop router is between the sender and RP.

Q:

How do you know who is the first hop router if there are multiple routers between sender and RP?

Dieg0M

No. The PIM DR is elected in a multi-access network if multiple PIM enabled devices are attached to the same segment. It could be in a segment between the receiver and the RP but it could also be in a segment between the sender and the RP. The role of the DR is to forward register messages on behalf of the source and join/prune messages from the receiver to the RP.

As for the first hop router, in the same manner as the DR, it could be a different device depending if it is the first hop router from the receivers or the sources perspective.

dppagc

Hi DiegoM,

I am confused. How many designated routers are there? Is there one between the (source and RP) & then another one between the (receiver and RP)?

What happens if there are 2 routers attached to the source? Is this possible?

Dieg0M

One per multi-access network, so you can have multiple between source and RP or receiver and RP.

As per 2 routers attached to the source, it is possible. Since they are in the same multi-access network, the router elected as DR will send the PIM register to the RP.