From: Joe Chang (changjoe@earthlink.net)
Date: Tue Aug 05 2003 - 03:19:26 GMT-3
In your scenario, did you alter the OSPF administrative distance on R5?
In rfc 2117 concerning this issue:
"A metric preference can be assigned per unicast routing protocol and needs
to be consistent for all routers on the multi-access network."
----- Original Message -----
From: "Brown, Patrick (NSOC-OCF}" <PBrown4@chartercom.com>
To: <ccielab@groupstudy.com>
Sent: Monday, August 04, 2003 11:18 AM
Subject: PIM designated forwarder election on multiaccess networks
> Group,
>
> In PIM-DM/PIM-SM the routers attached to the same multiaccess networks
send
> PIM assert messages to decide who will be the forwarder for that segment.
> Priority is given to Admin distance --> routing protocol metric --->
lastly
> the Highest IP on network.
>
> My topology: Frame-relay multipoint
> 132.15.74.1(lo0 = 132.15.1.1)
> / / \
> / / \
> / / \
> / / \
> (r4)(r3) (r5)
> |________|
>
> Problem:
>
> The multicast source is at the IP address of 132.15.74.4 off of r4.
> R3 has joined the multicast group 224.2.1.1. r5 is the PIM DR for the
> multiaccess segment between r3 and r5. When multicast packets are sent to
> this segment, r5 act as the PIM forwarder for this segment. Even though r3
> has a better admin distance and better metric for the route to the source
> address, and should be the forwarder. Note: r5 has e0 interface in OIL, so
> it's the forwarder.
>
> show outputs:
>
> r3)
> (132.15.74.4, 224.2.1.1), 00:00:05/00:02:54, flags: PT
> Incoming interface: Serial0/0, RPF nbr 132.15.74.1
> Outgoing interface list: Null
>
> r5)
> (132.15.74.4, 224.2.1.1), 00:00:38/00:02:21, flags: CLJT
> Incoming interface: Serial0, RPF nbr 132.15.74.1
> Outgoing interface list:
> Ethernet0, Forward/Sparse, 00:00:38/00:02:47
>
> note: r3 has lower admin distance and metric(cost)to the
source(132.15.74.4)
> r3)
> O 132.15.74.4/32 [110/128] via 132.15.74.1, 00:20:21, Serial0/0
> C 132.15.74.0/27 is directly connected, Serial0/0
>
> r5)
> O 132.15.74.4/32 [200/129] via 132.15.74.1, 00:04:22, Serial0
> C 132.15.74.0/27 is directly connected, Serial0
>
>
> I found something while writing this email!
>
> If the multicast source is 132.15.40.4, which is a subnet hanging off of
r4,
> it works! Note: r3 now has e0/0 in OIL, so it's the forwarder for this
(S,G)
> entry.
>
> r3)
> (132.15.40.4, 224.2.1.1), 00:00:05/00:02:54, flags:
> Incoming interface: Serial0/0, RPF nbr 132.15.74.1
> Outgoing interface list:
> Ethernet0/0, Forward/Sparse, 00:00:05/00:02:54
>
> r5)
> (132.15.40.4, 224.2.1.1), 00:00:37/00:02:22, flags: PCLJ
> Incoming interface: Serial0, RPF nbr 132.15.74.1
> Outgoing interface list: Null
>
> r3)
> O 132.15.40.0/24 [110/138] via 132.15.74.1, 00:29:26, Serial0/0
>
> r5)
> O 132.15.40.0/24 [200/139] via 132.15.74.1, 00:14:16, Serial0
>
>
>
> So what this is telling me:
> The router does not look at the OSPF /32 routes that was a result of
having
> a point 2 multipoint configuration, to make its PIM Forwader election
> decision. So it does not send this info in the Assert message.
>
>
> Is this correct!
>
>
> Thanks,
>
> Patrickb
>
>
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