Re: igmp querier , assert winner and DR confusion on election

This should help:

Quoted from CCIE Routing and Switching Exam Certification
Guide 4th Edition

"The PIM DR concept applies mainly when IGMPv1 is used.
IGMPv1 does not have a
mechanism
to elect a Querierbthat is to say that
IGMPv1 has no way to decide which of the
many routers on
a LAN should send
IGMP Queries. When IGMPv1 is used, the PIM DR is used as the
IGMP
Querier.
IGMPv2 can directly elect a Querier (the router with the lowest IP
address),
so the PIM
DR is not used as the IGMP Querier when IGMPv2 is used."
B Make a
small loan, Make a big difference - Kiva.org
________________________________
From: Mark_1982 <m.abghany_at_gmail.com>
To:
Bobola Oke <okebobola_at_gmail.com>
Cc: ehtesham ali <conect2ehtesham_at_gmail.com>;
imran ali <immrccie_at_gmail.com>;
Cisco certification <ccielab_at_groupstudy.com>
Sent: Sun, December 12, 2010 2:42:59 AM
Subject: Re: igmp querier , assert
winner and DR confusion on election

Hi Babola

DR is used in the IP Multicast
terminology (between routers and each other),
for the querier it's used to
handle the communication at the IGMP level
(between routers and host), most of
times its the same router

i know its a little bit confusing :)

BR/Mark

On
Sun, Dec 12, 2010 at 1:10 AM, Bobola Oke <okebobola_at_gmail.com> wrote:

>
Thanks for the reply Mark,
> but i still dont get the function of the DR. How
does it differ from the
> querier? anybody!
>
> Regards,
>
> On Fri, Dec 10,
2010 at 9:32 PM, Mark_1982 <m.abghany_at_gmail.com> wrote:
>
>>B Hi there
>>
>>
u have 3 phases of elections:
>>
>> 1-Querier elections, who will handle the
communication between a group of
>> hosts and a group of routers on the same
segment
>> 2-Designated Router Elections, who will handle the quey message
(Multicast
>> signalling)
>> 3-Desingated Forwarder, who will handle Multicast
traffic (video stream
>> for example)
>>
>> First the Querier Election
Process.
>> At start up each router sends a query message to the all systems
group
>> 224.0.0.1 from its own interface address. The router with the lowest
ip
>> address is elected IGMP querier.
>>
>> Second the PIM DR Election
Process
>> The router with the highest ip address is elected as PIM DR. This
>> selection process can also be influenced by configuring a pim DR priority.
>> By default all routers have priority 1, hence highest ip address wins by
>>
default. However if DR priority is used then highest DR priority wins.
>>
>>
The show igmp interface command can be used to show elected DR and querier
>>
>> *Third the Forwarder Election Process ( u will need to use Assert
>>
messaging as an election mechanism)*
>> These Assert Messages are used to
elect the PIM forwarder using the
>> following three rules:
>>
>>B B 1. The
router generating an Assert with the lowest Administrative
>>B B distance is
elected the forwarder.B The AD would only differ if the
routes
>>B B to R5
where from different routing protocols.B If the Administrative
>>B B
Distances are the same then we move to step 2.
>>B B 2. The best unicast
routing metric is used to break a tie if the
>>B B Administrative Distances
are the same.B The combination of AD and the
>>B B unicast routing metric
is referred to as a tuple. If metrics are the
same
>>B B them we move on to
step 3.
>>B B 3. The device with the highest IP Address will be elected as
the PIM
>>B B Forwarder.
>>
>> *Note:*u can make the three routers the same
router with some
>> manipulation in priority or IGP, but they are NOT the same
functions, its
>> administrative issue to be the same router or not
>>
>>
BR/Mark
>>
>>B On Thu, Dec 9, 2010 at 12:32 AM, ehtesham ali <
>>
conect2ehtesham_at_gmail.com> wrote:
>>
>>> thanks Babola ,
>>> sure experts will
help !B eagerly waiting for their comments ! just to
>>> point
>>> out that
DR is ONLY used forB Registration and sending IGMP join.
>>>
>>> Being DR
doesn't mean that it will always beB forwarder .
>>>
>>> Regards
>>>B On
Wed, Dec 8, 2010 at 11:29 PM, Bobola Oke <okebobola_at_gmail.com>
>>> wrote:
>>>
>>> > I highly recommend you study TCP/IP routing vol2. Deff Doyle does a
>>>
> fantastic job of explaining these clearly.
>>> >
>>> > For assert elections,
the router with the lowest cost to the source
>>> always
>>> > wins.
>>> >
>>>
> The designated router is the forwarder. (I'm not sure on this... I
>>> think
I
>>> > need to refer to the book myself :D). The IGMP querier checks if there
>>> are
>>> > hosts that want to receive multicast traffic. The forwarder does
the
>>> > forwarding :D
>>> >
>>> > If all the cost to reach the source were
to be the same. R3 would be
>>> the
>>> > designated router (forwarder) and R1
would be the querier. I think the
>>> rule
>>> > changes if IGMP version 1 and
PIM v1 is being used.
>>> >
>>> > I'm sure the experts can help further on
this! Just trying to do my
>>> bit...
>>> >
>>> >
>>> >
>>> >
>>> > On Wed,
Dec 8, 2010 at 4:54 PM, imran ali <immrccie_at_gmail.com> wrote:
>>> >
>>> > > hi
group ,
>>> > >
>>> > > R1 , R2 , R3 are connected on a multiaccess segmentB
sharing ip
>>> address
>>> > > from
>>> > > 10.1.123.X /24 subnet where X is
the router no .
>>> > >
>>> > > now when it comes to cost R2 is having lowest
cost to reach the
>>> SOURCE .
>>> > >
>>> > > All the router has equal cost
to Rp. igmp ver is 2
>>> > >
>>> > > question :
>>> > >
>>> > > 1) who will be
elected as assert forwarder ? DR ? Igmp Querier ?
>>> > >
>>> > > 1) I believe
all three roles are seprate or is there any overlap of
>>> > roles?
>>> > >
>>> > > i have read some where thatB igmp querier is the one who forwards the
>>> > > traffic on LANB but in my case R2 should be
>>> > > the Mcast data
forwarder .
>>> > >
>>> > > Regards
>>> > >
>>> > >
>>> > > Blogs and organic
groups at http://www.ccie.net
>>> > >
>>> > >
>>>
Received on Wed Dec 15 2010 - 13:51:10 ART