DR (Designated Router) in multicast

eemoon
eemoon used Ask the Experts™
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DR(designated router) is for sending source message to receiver. I am not sure DR is located between source and RP, or between RP to receiver? Anyone can give some idea? Thank you
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Distinguished Expert 2018
Commented:
Understanding Designated Routers
In a PIM sparse mode (PIM-SM) domain, there are two types of designated routers to consider:

   The receiver DR sends PIM join and PIM prune messages from the receiver network toward the RP.
   The source DR sends PIM register messages from the source network to the RP.

In any LAN environment, a DR will be elected by PIM (Protocol Independent Multicast) and in PIM-SM can be find on both places (between source and RP AND receiver and RP).

Author

Commented:
Thank you so much for your fast reply.
The document says if there are two path between source and RP, the DR needs to be selected. I would like to know if there is only one path between source and RP, does the DR need to be selected? and same for between RP and receiver?
Distinguished Expert 2018

Commented:
Even if there is only one multicast router on segment DR is still elected. If I remember correctly multipath in this case is referring to having 2 multicast routers on the same network segment, but still, even if there is only one multicast router, there will still be DR election.
It is the same in both cases (source and receiver DR).

Author

Commented:
Thank you!
Distinguished Expert 2018

Commented:
You're welcome.

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