Re: More Multicast Understanding

Bryan,

Thanx again for your support. I have labbed your scenario:
R1----LAN1----R2/R3----LAN2----R4

Just to confirm things R1 is the streamer and the RP. R2 has a preferred
path to the the loopback of R1(source of the stream).

R2#show ip route ospf
     1.0.0.0/32 is subnetted, 1 subnets
O 1.1.1.1 [110/3] via 123.0.0.1, 00:12:01, Ethernet0/0

R3#show ip route ospf
     1.0.0.0/32 is subnetted, 1 subnets
O 1.1.1.1 [110/11] via 123.0.0.1, 00:09:58, Ethernet0/0

R3 is the designated router on both subnets (R1,R2,R3) and (R2,R3) wich has
the client of R4.

R3#SHOW IP pim interface
Address Interface Ver/ Nbr Query DR DR
                                          Mode Count Intvl Prior
123.0.0.3 Ethernet0/0 v2/S 2 30 1
123.0.0.3
23.0.0.3 Ethernet0/1 v2/S 1 30 1
23.0.0.3

R2:
*Mar 1 00:28:34.879: IP(0): s=1.1.1.1 (Ethernet0/0) d=239.1.1.1 id=176,
ttl=253
, prot=1, len=114(100), mroute olist null
R3:
*Mar 1 00:27:06.951: IP(0): s=1.1.1.1 (Ethernet0/0) d=239.1.1.1
(Ethernet0/1) i
d=173, ttl=253, prot=1, len=100(100), mforward

ON R3:
1.1.1.1, 239.1.1.1), 00:00:12/00:02:50, flags: JT
 Incoming interface: Ethernet0/0, RPF nbr 123.0.0.1
 Outgoing interface list:
   Ethernet0/1, Forward/Sparse, 00:00:12/00:02:47

This shows that in my scenario R3 is the one forwarding the traffic to the
segment.

Note that when on R2 I issued the command ip pim dr-priority 255. The
behavior was reversed what I mean is:
R2 is forwarding now:
*Mar 1 00:34:08.707: IP(0): s=1.1.1.1 (Ethernet0/0) d=239.1.1.1
(Ethernet0/1) i
d=189, ttl=253, prot=1, len=100(100), mforward
(1.1.1.1, 239.1.1.1), 00:01:33/00:02:00, flags: JT
  Incoming interface: Ethernet0/0, RPF nbr 123.0.0.1
  Outgoing interface list:
    Ethernet0/1, Forward/Sparse, 00:01:33/00:02:55, A

R3 is not forwarding traffic anymore:
*Mar 1 00:32:46.871: IP(0): s=1.1.1.1 (Ethernet0/0) d=239.1.1.1 id=192,
ttl=253
, prot=1, len=114(100), mroute olist null
(1.1.1.1, 239.1.1.1), 00:04:20/00:00:43, flags: PJT
  Incoming interface: Ethernet0/0, RPF nbr 123.0.0.1
  Outgoing interface list: Null

This is the model of the router as well as the image.

Note that I am doing my simulation using dynamips.

(C3640-JS-M), Version 12.4(17)

Best Regards,

On Fri, Oct 16, 2009 at 5:27 PM, Bryan Bartik <bbartik_at_ipexpert.com> wrote:

> 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,
>>
>>
>> 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
Blogs and organic groups at http://www.ccie.net