From: Salau, Yemi (yemi.salau@siemens.com)
Date: Tue May 20 2008 - 09:11:51 ART
Ok, when IGMPv1 was developed, the DR and IGMP Querier concept was
engolved in one entity component...ie. a Router can be the DR and the
IGMP Querier on the same subnets and this is always the case. Check out
RFC 1112. The election is solely the responsibility of PIM Election
Process which uses priority concept.
But with the inception of IGMPv2 as defined in RFC 2236, the 2 functions
are decoupled, meaning one router can be the DR (from PIM's perspective)
and another can be the Querier (From IGMPv2's perspective)
I know you already know the difference between a Queirer and a DR, so
I'll save you some bandwidth. But on Cisco Router's implementation of
RFC2236, the DR is the router with the highest IP address on the subnet,
whereas the IGMP querier is the router with the lowest IP address.
Check out the "Routers That Run IGMPv2" section of this Cisco Docs:
http://www.cisco.com/en/US/docs/ios/12_4/ip_mcast/configuration/guide/mc
bcigmp.html#wp1086745
Many Thanks
Yemi Salau
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
Roger RPF
Sent: Tuesday, May 20, 2008 12:40 PM
To: 'Sadiq Yakasai'
Cc: ccielab@groupstudy.com
Subject: AW: Multicast Assert Messages in PIM-SM - Designated Forwarder?
Hi Sadiq,
Thanks for your message...but I think not everything is clear to me :o(
If we have two routers on a LAN (and use IGMPv2 and PIM-SM), one of them
will be the active IGMP querier (router with the lowest IP address).
Which
one of the two routers will send the PIM join towards the RP? The IGMP
querier or the other router? If it is not the IGMP querier, the other
router
listens to the IGMP join from the host and start's the PIM join, isn't
it?
If that's the case, how does the IGMP querier know that he does not have
to
execute the PIM-join?
When in this process and how exactly starts the forwarder election
through
the assert messages?
So far I was always thinking that the IGMP querier will also initiate
the
PIM-join towards the RP and also be the designated forwarder, i.e.
forwards
the traffic into the LAN but that's not the fact or do I mix again
something
up?
Who starts the PIM join?
In Jeff Doyle Vol2 Page 410 he says:" The querier is responsible for
forwarding the multicast stream. The other router or routers only
listen,
and they begin forwarding the stream only if the querier fails"
I do also not understand what you mean with
"While the Designated Router is responsible for delivering mcast traffic
**FROM** a LAN segment"
I mean, we do not send multicast traffic off the LAN, it's only a "one
way
direction" into the LAN, isn't it?
Sorry, but I get more confused :o)) Would be really happy if you can
clarify
that in regards of IGMPv2 and PIM-SM.
Thank you
Roger
-----Urspr|ngliche Nachricht-----
Von: Sadiq Yakasai [mailto:sadiqtanko@gmail.com]
Gesendet: Dienstag, 20. Mai 2008 12:05
An: Roger RPF
Cc: ccielab@groupstudy.com
Betreff: Re: Multicast Assert Messages in PIM-SM - Designated Forwarder?
HI Roger,
I think you are mixing up two different roles and direction as far as
MCAST traffic forwarding goes:
The Designated Forwarder is responsible for delivering MCAST traffic
from the source (or RP) **TO** the LAN segment (having more than one
entry/exit point) where the receivers of the traffic are located. The
Assert message is used to elect the router to be used as a DF (higher
IP address wins).
While the Designated Router is responsible for delivering mcast
traffic **FROM** a LAN segment (whether there is only one or multiple
exit points). You are right in that in IGMPv1, the DR is the same as
the Querier automatically.
While in IGMPv2, a DR could be different from the Querier. In this
case, the DR is elected based on the highest IP adress while the
Querier election is based on the Lower IP address.
Hope that clears up the air a little bit more.
Sadiq
This archive was generated by hypermail 2.1.4 : Mon Jun 02 2008 - 06:59:17 ART