Re: multicast terms

Hi Khalid,

The ICMPv1 Querier is a router responsible for sending all IGMPv1
Queries on a subnet (instead of having all the routers send Queries).
This router is elected as a Designated Router (DR) for the subnet by the
Layer 3 IP Multicast Routing protocol (e.g. PIM).
With ICMPv2 there is no DR as the router performing the role of Querier
is elected by the Querier election process - it contrasts with ICMPv1 as
it does not depend upon the IP Multicast Routing protocol. Instead it is
a feature built into ICMPv2.
With regards to the term Multicast Forwarder are you referring to the
multicast forwarding process? If so one mechanism used to determine
whether to forward or drop an incoming multicast packet is have the
router perform a Reverse Path Forwarding (RPF) on the packet. If the RPF
check is successful, the packet is forwarded; otherwise, it is dropped.
Whether this check is performed against a separate multicast routing
table or the existing unicast routing table depends upon the routing
protocol is use - DVMRP, PIM, etc.

regards Andy

Syed Khalid Ali wrote:
> dear group:
> can any one explain the difference between the Querier, DR and Forwarder?
> thanksKhalid
>
>
>
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Received on Sat Feb 27 2010 - 14:11:08 ART