Re: More Multicast Understanding

Karim,

You should lab this scenario. It is very easy to do with 4 routers. The
winner of the ASSERT process forwards traffic on the LAN, this may or may
not be the DR.

On Thu, Oct 15, 2009 at 1:26 PM, karim jamali <karim.jamali_at_gmail.com>wrote:

> Thank You Bryan,
>
> What you are saying is that the DF is the one that will forward traffic to
> the subnet. However as far as I know the forwarder on a common subnet is
> elected based on:
> 1)Administrative distance of the route to the source.
> 2)Metric of the route to the source.
> 3)Highest IP address on the subnet.
>
> Supposedly one router is elected as forwarder, the command ip pim
> dr-priority makes the other router the designated router on the segment and
> is the one that forwards traffic to the segment.
>
> This is what I want to understand?Is the designated router the router that
> forwards to the segment?
>
> Waiting for yor help experts!
>
> On Thu, Oct 15, 2009 at 6:41 PM, Bryan Bartik <bbartik_at_ipexpert.com>wrote:
>
>> Karim,
>>
>> The DR and DF work in different direction. DF is responsible for sending
>> joins up to the RP and thus forwarding traffic onto the LAN. The DR is
>> responsible for registering with the RP when a new source is heard. Consider
>> this topology:
>>
>> R1-----LAN1-----R2/R3-----LAN2-----R4
>>
>> R2 and R3 are connected to LAN1 with R1, and LAN2 with R4.
>> R1 is the RP.
>> If R4 is a client, then the winner of the ASSERT process between R2 and R3
>> on LAN2, sends joins up to R1.
>> If R4 is a server, then the DR on LAN2 sends REGISTERS to R1.
>>
>> -hth
>>
>>
>> On Thu, Oct 15, 2009 at 7:50 AM, karim jamali <karim.jamali_at_gmail.com>wrote:
>>
>>> ---------- Forwarded message ----------
>>> From: karim jamali <karim.jamali_at_gmail.com>
>>> Date: Wed, Oct 14, 2009 at 10:04 AM
>>> Subject: Fwd: More Multicast Understanding
>>> To: Narbik Kocharians <narbikk_at_gmail.com>, smorris_at_ine.com, Anthony
>>> Sequeira
>>> <asequeira_at_internetworkexpert.com>, petr_at_internetworkexpert.com
>>>
>>>
>>>
>>>
>>> ---------- Forwarded message ----------
>>> From: karim jamali <karim.jamali_at_gmail.com>
>>> Date: Wed, Oct 14, 2009 at 10:04 AM
>>> Subject: More Multicast Understanding
>>> To: Cisco certification <ccielab_at_groupstudy.com>
>>>
>>>
>>> Dear Experts,
>>>
>>> I have a weird issue which I am not getting in multicast, especially
>>> which
>>> router will forward to the segment in case of two routers for instance. I
>>> have sent an enquiry on groupstudy and got a great article stating that
>>> the
>>> forwarder on every subnet will be elected based on :
>>>
>>> 1)Best Administrative Distance to the source
>>> 2)Best Metric
>>> 3)Highest IP address of the two competing routers.
>>>
>>> This is A PIM SPARSE MODE SCENARIO
>>>
>>> This made perfect sense to me and I understood how forwarders were
>>> elected
>>> on a shared segment, until I got shocked with the fact that seemed very
>>> strange to me. It seems that the designated router on a segment is what
>>> determines who will forward on the common subnet. In the attached file, I
>>> have a streamer,2 backbones devices and a common subnet. On the basis of
>>> election, it was clear to me that the highest IP address (BB2) will win
>>> the
>>> election and be the forwarder, and by default it was.
>>>
>>> show ip igmp int command shows me two things : Who is the Querier on the
>>> subnet and who is the Designated Router, there is no mention for the
>>> forwarding router on th segment. Can someone please explain this?
>>>
>>> The thing that completely shocked me that wheneve I use the command ip
>>> pim
>>> dr-priority <255> for example on the Querier, it also becomes the
>>> Designated
>>> router and it is the one that forwards the multcast traffic on the
>>> subnet,
>>> without any respect to who is the forwarder and how it it elected(3 steps
>>> above).. Please can someone clarify for me the role of the designated
>>> router,is it the forwarder on the subnet?
>>>
>>> As far as I remember, the DR is the router which gets the stream,and
>>> notifies the Rendezvous Point (RP) that a stream exists by sending a
>>> register message. But here I see it affecting how traffic is forwarded on
>>> the client side.
>>>
>>> I would truly be glad if someone can sort this confusion out!
>>>
>>> Best Regards,
>>>
>>> Karim
>>>
>>>
>>>
>>>
>>>
>>> --
>>> KJ
>>>
>>>
>>>
>>> --
>>> KJ
>>>
>>>
>>> Blogs and organic groups at http://www.ccie.net
>>>
>>> _______________________________________________________________________
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>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>
>>
>> --
>> Bryan Bartik
>> CCIE #23707 (R&S), CCNP
>> Sr. Support Engineer - IPexpert, Inc.
>> URL: http://www.IPexpert.com <http://www.ipexpert.com/>
>>
>
>
>
> --
> KJ
>

-- 
Bryan Bartik
CCIE #23707 (R&S), CCNP
Sr. Support Engineer - IPexpert, Inc.
URL: http://www.IPexpert.com
Blogs and organic groups at http://www.ccie.net