From: Brown, Patrick (NSOC-OCF} (PBrown4@chartercom.com)
Date: Mon Aug 04 2003 - 15:18:56 GMT-3
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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