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:
>
>> 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:
>>
>> 1. The router generating an Assert with the lowest Administrative
>> distance is elected the forwarder. The AD would only differ if the
routes
>> to R5 where from different routing protocols. If the Administrative
>> Distances are the same then we move to step 2.
>> 2. The best unicast routing metric is used to break a tie if the
>> Administrative Distances are the same. The combination of AD and the
>> unicast routing metric is referred to as a tuple. If metrics are the
same
>> them we move on to step 3.
>> 3. The device with the highest IP Address will be elected as the PIM
>> 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
>>
>> On Thu, Dec 9, 2010 at 12:32 AM, ehtesham ali <
>> conect2ehtesham_at_gmail.com> wrote:
>>
>>> thanks Babola ,
>>> sure experts will help ! eagerly waiting for their comments ! just to
>>> point
>>> out that DR is ONLY used for Registration and sending IGMP join.
>>>
>>> Being DR doesn't mean that it will always be forwarder .
>>>
>>> Regards
>>> 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 segment 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 that igmp querier is the one who forwards the
>>> > > traffic on LAN but in my case R2 should be
>>> > > the Mcast data forwarder .
>>> > >
>>> > > Regards
>>> > >
>>> > >
>>> > > Blogs and organic groups at http://www.ccie.net
>>> > >
>>> > >
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>>> > >
>>> >
>>> >
>>> > --
>>> > Bobola Oke
>>> >
>>> >
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>>
>
>
> --
> Bobola Oke

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Received on Sun Dec 12 2010 - 09:42:59 ART