Multicasting querier Highest or Lowest IP?

rakem

found some conflicting statements regarding the Querier election in IGMPv2.

in the train signal multicasting section Chris Bryant says that the "router with the lowest IP address is the querier"

in the CCNP self study book on page 604?: "router with the highest IP address is the designated querier"

in the CCNP official exam cert guide on page 484: "all routers start as queries and transition to non queries if they hear another querier with a higher IP address"

so can anyone tell me which is correct?

dtlokee

With IGMP v2 the querier is the one with the lowest IP address, but in IGMP v 1 the idea of a querier (designated router) is elected via the routing protocol AD and metric.

Or atleast that is my understanding but I flubbed multicast on my last lab attempt so what do I know

rakem

bah this is confusing... found this cisco link:

"For IGMP Versions 2 and 3, the designated querier is the highest IP-addressed multicast router on the subnet"

http://www.cisco.com/en/US/docs/ios_xr_sw/iosxr_r2.0/multicast/command/reference/3mrigmp.html

hmm i think im just gonna lab it up and find out for my self.

tomset

I'm having the same problem. I've seen the conflicting statements as well and I'm not sure what to believe. Are designated queriers in IGMP v2 elected by the highest or lowest IP on the subnet?

jezg76

I am a self proclaimed newb but here is my understanding of this...

Designated Router (DR) used on IGMPv1 to send Membership Queries and it uses the highest IP on a segment.

Designated Querier - Used for IGMPv2 to send Membership Queries and it uses the lowest IP address of a segment.

Forwarder - Used to send multicast traffic onto a segment when interfaces receive assert messages on an interface that they sent an assert message. First, it compares AD and metric, and if they are tied, highest IP wins.

So, in essence, a router's interface could be the Designated Querier on a segment while another router's interface is the Forwarder.

I hope this is close to being correct because if it isn't, I guess I have some re-reading to do.

If I am wrong, by all means correct me because I am taking the BSCI in the coming weeks.

tomset

jezg76 wrote:

If I am wrong, by all means correct me because I am taking the BSCI in the coming weeks.

I'm taking it tomorrow!! lol

miller811

Here are the notes I took on the subject in the last few days.

In V1, the DR and Querier are usually the Same, in V2 they are not.
In V2, the highest IP is the DR and lowest IP is the Querier.

oxzgan

In IGMP v1 PIM Desgnated router responsible for 2 things
a ) for sending pim register , pim join/prune
b ) for sending query messages

in IGMP v2 its decoupled
querier only sends query , pim DR forwards muticast