From: Fred Ingham (fingham@xxxxxxx)
Date: Mon Aug 19 2002 - 23:12:12 GMT-3
This is one of the examples in the RS-NMC-1 (NetMasterClass) course. The
purpose of the exercise was to show exactly what you have specified, and
then to have you solve it. The solution depends on the type of OSPF network
used in the hub and spoke configuration.
Look at the R1 mroute table first. The (*,232.2.2.2) has the correct RP
address (104.1) and the correct interface (s0/0.2). Note that there is no
(S, G) (172.16.35.5, 232.2.2.2). This is probably because you did not have
a continuous ping on R5 to generate traffic. R1 is congruent with the
multicast tree because you specified an OSPF cost on R1 S0/0.1 that makes
S0/0.2 the preferred path to the RP and to the source. R1 is passing the
location of the RP to R2. S0/0.1 has been pruned for the (*,G) .
Now look at the mroute table on R2. The (*.232.2.2.2) has the correct RP
address but the RPF is 172.16.123.3. The is no (S,G) nor will there be any
since the RPF to the source is also 123.3. This is a function of how OSPF
works with a non-broadcast (or broadcast) network type. The originating
router, in this case, R3, is the next hop and hence the RPF. If you used a
PTMP network type on the hub and spoke network then the next hop would have
been R1, the hub, and life would be good.
So, to get the multicast to work from R2 (and R6 behind R2) you need to
change the RPF from 123.3 to 123.1. You could change the OSPF network type
as explained above, vary OSPF cost on the R3 S0/0 interface, or use static
mroutes. In this case you would want a static mroute to the RP and to the
source. Note that static mroutes do not show up in the IP routing table (in
case you were worried about using static routes).
The form would be ip mroute 172.16.104.1 255.255.255.0 172.16.123.1 and
ip mroute 172.16.32.0 255.255.252.0 172.16.123.1.
Have fun. These and other details are/were explained in the NMC-1 course.
Once you have changed configs, the mtrace command is useful to show the
reverse route.
Cheers, Fred
----- Original Message -----
From: "CCIE2B" <ccie2b@cox.net>
To: <ccielab@groupstudy.com>
Sent: Wednesday, September 18, 2002 3:23 AM
Subject: Multicast over a P2M FR link...
> Group,
>
> I was wondering if someone could help me understand this multicast
> behavior...
>
> R1 (MA) is connected to R2 and R3 via p2m links and to R4 (Auto-RP) via a
p2p
> link. On R1, I do not see S0.1 as an outgoing interface for
(*,232.2.2.2).
> From R1 the routing table is congruent with the multicast shared tree.
>From
> R2, the router thinks that the RPF for group 232.2.2.2 is via 172.16.123.3
> (other FR spoke). There is no multicast connection between R1 and R3.
Why is
> R1 not showing interface s0.1 as an outgoing interface for group
232.2.2.2?
> And why does R2 think that R3 should be the next reverse path router to
the
> source? The source is connected to R3. Thanks in advance...
>
> r1#sh run int s0.1
> interface Serial0.1 multipoint
> ip address 172.16.123.1 255.255.255.0
> ip pim sparse-dense-mode
> ip ospf network non-broadcast
> ip ospf cost 200
> frame-relay map ip 172.16.123.1 103 broadcast
> frame-relay map ip 172.16.123.2 102 broadcast
> frame-relay map ip 172.16.123.3 103 broadcast
> no frame-relay inverse-arp
> end
>
> interface Serial0.2 point-to-point
> ip address 172.16.14.1 255.255.255.0
> ip pim sparse-dense-mode
> frame-relay interface-dlci 104
> end
> r1#
>
> r1#sh ip mroute
> (*, 224.0.1.39), 00:13:26/00:00:00, RP 0.0.0.0, flags: DJCL
> Incoming interface: Null, RPF nbr 0.0.0.0
> Outgoing interface list:
> Serial0.2, Forward/Sparse-Dense, 00:13:26/00:00:00
> Serial0.1, Forward/Sparse-Dense, 00:13:26/00:00:00
> Loopback0, Forward/Sparse-Dense, 00:13:26/00:00:00
>
> (172.16.104.1, 224.0.1.39), 00:12:59/00:02:01, flags: CLTA
> Incoming interface: Serial0.2, RPF nbr 172.16.14.4
> Outgoing interface list:
> Loopback0, Forward/Sparse-Dense, 00:12:59/00:00:00
> Serial0.1, Forward/Sparse-Dense, 00:12:59/00:00:00
>
> (*, 224.0.1.40), 00:13:26/00:00:00, RP 0.0.0.0, flags: DJCL
> Incoming interface: Null, RPF nbr 0.0.0.0
> Outgoing interface list:
> Serial0.2, Forward/Sparse-Dense, 00:13:27/00:00:00
> Serial0.1, Forward/Sparse-Dense, 00:13:27/00:00:00
> Loopback0, Forward/Sparse-Dense, 00:13:27/00:00:00
>
> (172.16.101.1, 224.0.1.40), 00:12:40/00:02:15, flags: CLTA
> Incoming interface: Loopback0, RPF nbr 0.0.0.0
> Outgoing interface list:
> Serial0.1, Forward/Sparse-Dense, 00:12:40/00:00:00
> Serial0.2, Forward/Sparse-Dense, 00:12:40/00:00:00
>
> (*, 232.2.2.2), 00:13:27/00:00:00, RP 172.16.104.1, flags: SJCL
> Incoming interface: Serial0.2, RPF nbr 172.16.14.4
> Outgoing interface list:
> Loopback0, Forward/Sparse-Dense, 00:13:27/00:02:31
>
>
> r1#sh ip route
> O 172.16.32.0/22 [110/75] via 172.16.14.4, 00:44:41, Serial0.2
> C 172.16.14.0/24 is directly connected, Serial0.2
> C 172.16.1.0/24 is directly connected, Ethernet0
> C 172.16.123.0/24 is directly connected, Serial0.1
> O 172.16.105.1/32 [110/76] via 172.16.14.4, 00:40:50, Serial0.2
> O 172.16.104.1/32 [110/65] via 172.16.14.4, 00:40:51, Serial0.2
>
> r2#sh run int s0
> interface Serial0
> ip address 172.16.123.2 255.255.255.0
> ip pim sparse-dense-mode
> encapsulation frame-relay IETF
> ip ospf network non-broadcast
> ip ospf priority 0
> no fair-queue
> frame-relay map ip 172.16.123.1 201 broadcast
> frame-relay map ip 172.16.123.2 201 broadcast
> frame-relay map ip 172.16.123.3 201 broadcast
> no frame-relay inverse-arp
> frame-relay lmi-type ansi
> end
> r2#
>
> r2#sh ip mroute
> (*, 224.0.1.39), 00:12:22/00:02:59, RP 0.0.0.0, flags: DJC
> Incoming interface: Null, RPF nbr 0.0.0.0
> Outgoing interface list:
> Serial0, Forward/Sparse-Dense, 00:12:22/00:00:00
> Ethernet0, Forward/Sparse-Dense, 00:12:22/00:00:00
>
> (172.16.104.1, 224.0.1.39), 00:11:49/00:02:10, flags: PCTA
> Incoming interface: Serial0, RPF nbr 172.16.123.3
> Outgoing interface list:
> Ethernet0, Prune/Sparse-Dense, 00:11:49/00:00:16
>
> (*, 224.0.1.40), 00:12:23/00:00:00, RP 0.0.0.0, flags: DJCL
> Incoming interface: Null, RPF nbr 0.0.0.0
> Outgoing interface list:
> Serial0, Forward/Sparse-Dense, 00:12:23/00:00:00
> Ethernet0, Forward/Sparse-Dense, 00:12:25/00:00:00
>
> (172.16.101.1, 224.0.1.40), 00:12:25/00:02:53, flags: CLT
> Incoming interface: Serial0, RPF nbr 172.16.123.1
> Outgoing interface list:
> Ethernet0, Forward/Sparse-Dense, 00:12:25/00:00:00
>
> (*, 232.2.2.2), 00:12:25/00:00:00, RP 172.16.104.1, flags: SJCL
> Incoming interface: Serial0, RPF nbr 172.16.123.3
> Outgoing interface list:
> Ethernet0, Forward/Sparse-Dense, 00:11:30/00:02:58
> Loopback0, Forward/Sparse-Dense, 00:12:25/00:02:05
>
> r2#sh ip route
> O 172.16.32.0/22 [110/74] via 172.16.123.3, 00:42:10, Serial0
> O 172.16.14.0/24 [110/128] via 172.16.123.1, 00:42:10, Serial0
> O 172.16.1.0/24 [110/74] via 172.16.123.1, 00:42:10, Serial0
> C 172.16.123.0/24 is directly connected, Serial0
> O 172.16.105.1/32 [110/75] via 172.16.123.3, 00:42:10, Serial0
> O 172.16.104.1/32 [110/75] via 172.16.123.3, 00:42:11, Serial0
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