From: Brian Dennis (bdennis@internetworkexpert.com)
Date: Mon Aug 14 2006 - 19:33:37 ART
As per RFC 2328 (OSPF Version 2) this is what you should expect to see. Point-to-multipoint and loopback network types do not advertise out the network itself. They only advertise out a /32.
<RFC 2328>
12.4.1.4. Describing Point-to-MultiPoint interfaces
For operational Point-to-MultiPoint interfaces, one or
more link descriptions are added to the router-LSA as
follows:
o A single Type 3 link (stub network) is added with
Link ID set to the router's own IP interface
address, Link Data set to the mask 0xffffffff
(indicating a host route), and cost set to 0.
o For each fully adjacent neighbor associated with the
interface, add an additional Type 1 link (point-to-
point) with Link ID set to the Router ID of the
neighboring router, Link Data set to the IP
interface address and cost equal to the interface's
configured output cost.
</RFC 2328>
http://www.internetworkexpert.com/rfc/rfc2328.txt
As you can see the RFC does not say anything about advertising out the network, just the /32's. This is done because the network type is designed to support a situation where there isn't direct layer two reachability between the routers. Think about a situtation where you have a hub and spoke Frame Relay network with 2 hubs and 50 spokes all on the same logical IP network. Each spoke would need 2 mappings to the hubs and 49 mappings to the other spokes. Now add a new spoke to the network and you would have to go to all of the other spokes and add the Frame Relay mapping to the new spoke. But if you run OSPF and used the point-to-multipiont network type the adding of a new spoke wouldn't require any additional configuration on the existing spokes. This is because the existing spokes will automatically learn about the new spoke from the hub routers when they advertise down the new spoke's /32.
HTH,
Brian Dennis, CCIE #2210 (R&S/ISP-Dial/Security)
bdennis@internetworkexpert.com
Internetwork Expert, Inc.
http://www.InternetworkExpert.com
Toll Free: 877-224-8987
Direct: 775-745-6404 (Outside the US and Canada)
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of Hash Aminu
Sent: Monday, August 14, 2006 2:58 PM
To: Cisco certification
Subject: /32 routes with poit to multipoint issue
Hello GS
i am just wondering that if this is a normal behaviour and cannot find any documentation to proove it it you have a frame-relay network with a hub and spoke and you use point to multipoint network all the routes related to the frame relay interfaces are shon as /32 routes while in escence they are /24s. any ideas will help
TIA
Hash
r2(config-if)# do sh ip ro
Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2
i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, * - candidate default, U - per-user static route
o - ODR, P - periodic downloaded static route
Gateway of last resort is not set
2.0.0.0/8 is variably subnetted, 7 subnets, 3 masks
C 2.2.2.0/24 is directly connected, Loopback0
C 2.2.12.0/24 is directly connected, FastEthernet0/0.14
C 2.2.23.0/25 is directly connected, FastEthernet0/0.11
O IA 2.2.56.0/24 [110/65] via 2.2.235.5, 00:15:03, Serial0/0
O 2.2.235.3/32 [110/128] via 2.2.235.5, 00:15:03, Serial0/0
C 2.2.235.0/24 is directly connected, Serial0/0
O 2.2.235.5/32 [110/64] via 2.2.235.5, 00:15:03, Serial0/0
r2(config-if)#
B.Eng, MCP,CCNA, CCNP
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