Re: More Multicast Understanding

Karim,

What IOS are you using? Look at my example and tell me if this is not what
you see.

R1----LAN1----R2/R3----LAN2----R4

R1 is RP and sender, sending from loopback at 1.1.1.1
R2's route metric is 3, R3's is 72 (manually manipulated cost)

R2#sho ip route 1.1.1.1
Routing entry for 1.1.1.1/32
  Known via "ospf 1", distance 110, metric 3, type intra area
  Last update from 192.168.234.3 on FastEthernet1/0, 00:00:39 ago
  Routing Descriptor Blocks:
  * 192.168.234.3, from 1.1.1.1, 00:00:39 ago, via FastEthernet1/0
      Route metric is 3, traffic share count is 1

R3#sho ip rou 1.1.1.1
Routing entry for 1.1.1.1/32
  Known via "ospf 1", distance 110, metric 72, type intra area
  Last update from 192.168.234.2 on FastEthernet1/0, 00:00:01 ago
  Routing Descriptor Blocks:
  * 192.168.234.2, from 1.1.1.1, 00:00:01 ago, via FastEthernet1/0
      Route metric is 72, traffic share count is 1

Now on LAN2 connected to R4, R3 is the DR:

R3#sho ip pim interface
Address Interface Ver/ Nbr Query DR DR
                                          Mode Count Intvl Prior
192.168.123.3 FastEthernet0/0 v2/S 2 30 1
192.168.123.3
192.168.234.3 FastEthernet1/0 v2/S 2 30 400
192.168.234.3

R2#sho ip pim int
Address Interface Ver/ Nbr Query DR DR
                                          Mode Count Intvl Prior
192.168.123.2 FastEthernet0/0 v2/S 2 30 1
192.168.123.3
192.168.234.2 FastEthernet1/0 v2/S 2 30 200
192.168.234.3
R2#

R4 has joined 239.1.1.1. When R1 sends traffic to 239.1.1.1, R2 is
forwarding it. We verify by looking at the mroute (you can also view mroute
counts to see that R3 is dropping, and R2 is forwarding).

R1#ping 239.1.1.1 sou lo 0 re 100

R2#sho ip mroute 1.1.1.1 239.1.1.1 | be \(
(1.1.1.1, 239.1.1.1), 00:00:37/00:03:27, flags: T
  Incoming interface: FastEthernet0/0, RPF nbr 192.168.123.1
  Outgoing interface list:
    FastEthernet1/0, Forward/Sparse, 00:00:37/00:03:20

R3#sho ip mroute 1.1.1.1 239.1.1.1 | be \(
(1.1.1.1, 239.1.1.1), 00:01:05/00:02:59, flags: PTX
  Incoming interface: FastEthernet1/0, RPF nbr 192.168.234.2
  Outgoing interface list: Null

R2 is forwarding but R3 is the DR. Is this how you are testing?

On Fri, Oct 16, 2009 at 7:12 AM, karim jamali <karim.jamali_at_gmail.com>wrote:

> Dear Experts,
>
> I understand that the DR from the server side, is the 1st router receiving
> the stream or in case of two routers one will be elected,and this router is
> the one that informs the RP that a stream exists (Register message),and the
> RP will send a register stop. On the client side,I understand that one of
> the two routers on the segment is supposed to communicate with the RP
> informing it that a client wants to listen to a certain group.
>
> The thing that is confusing me is from an article I read, I understood that
> the forwarder on a segment will be elected based on:
> 1)Best Administrative Distance to the souce
> 2)Best Metric to the source
> 3)Highest IP address.
>
>
> Scenario:
> PIM SPARSE MODE (RP on loopback of BB1)
> R1(STREAMER) -->LAN 1
> BB1-->LAN 1
> BB2-->LAN 1
>
> BB1-->LAN 2
> BB2-->LAN 2
> R4(CLIENT)-->LAN 2
>
> 1)When everything was left at its default.BB2 was the one forwarding on the
> segment,and this makes perfect sense since both BB1 and BB2 are connected
> to
> the stream (Same AD,Same Metric), so what determined the forwarder was the
> highest IP address (BB2).
>
> 2)When I used the command ip pim dr-priority <255> on BB1, the pim neighbor
> relationship was re-established and BB1 was the one forwarding on the
> segment. I used to think that the DR is only responsible for communicating
> with the RP and is not the one who will forward on the segment. I thought
> that the forwarder only depends on the 3 stated rules above. When I gave
> BB2
> a higher priority (ip pim dr-priority 256) it began forwarding again and
> BB1
> stopped forwarding.
>
> This is what is confusing me.
>
> I would be grateful if you can help me.
>
> Best Regards,
>
>
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-- 
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