PIM DR vs. multicast querier

[milan.kulik]

Hello,

Could anybody explain what's the difference between PIM Designated Router and multicast querier?

I thought it was the same but in CCNP Training Book I read

"The PIM router with the highest IP address becomes the DR for LAN"

and on another place

"The multicast router with the lowest IP address on the LAN segment is elected the multicast querier."

So what's the difference?

Or is there just a mistake in the book?

Thanks,

Milan

[thisisshanky]

I think the author refers to IGMP querier as multicast querier. The IGMP query election is based either on source ip or mac. (with the lowest ip or mac winning the election)

[milan.kulik]

Yes, they mean IGMP querier.

But the questions are:

Is it the same as PIM DR? (I think not, PIM DR with highest IP wins.)

If not, what's the difference?

Regards,

Milan

[thisisshanky]

The DR is used to find out RPs and register with it, while the IGMP querier is solely for listening to multicast groups on segments. So both are totally different.

[bbranch · Accepted solution]

The router with the highest IP address on a segment becomes the PIM DR, this router is responsible for registering with the Rendezvous Point for the directly connected sources, joining the distribution tree and forwarding traffic to networks with receivers.

The router with the lowest IP address on a segement becomes the IGMPv2 querier, this router is responsible for sending IGMP Group Membership queries and maintaing state for each active Multicast Group

How often a PIM router sends Hello messages (used by the DR election process) is controlled by the "ip pim query-interval " command, this could be where the confussion occured