Point-to-MultiPoint networks have been designed to work simply and naturally when faced with partial mesh connectivity. In Point-to-MultiPoint mode, OSPF treats all router-to-router connections over the non-broadcast network as if they were point-to-point links. No Designated Router is elected
for the network, nor is there an LSA generated for the network. It may be necessary to configure the
set of neighbors that are directly reachable over the Point-to-MultiPoint network. Each neighbor
is identified by its IP address on the Point-to-MultiPoint network. Because no Designated Routers
are elected on Point-to-MultiPoint networks, the Designated Router eligibility of configured
neighbors is undefined.Alternatively, neighbors on Point-to-MultiPoint networks may be dynamically discovered by
lower-level protocols such as Inverse ARP. In contrast to NBMA networks, Point-to-MultiPoint
networks have the following properties:
1.Backup Designated Router for a Point-to-MultiPoint network. No network-LSA is originated for
Point-to-MultiPoint networks. Router Priority is not configured for Point-to-MultiPoint
interfaces, nor for neighbors on Point-to-MultiPoint networks.
2. When originating a router-LSA, Point-to-MultiPoint interface is reported as a collection of
“point-to-point links” to all of the interface’s adjacent neighbors, together with a single stub link
advertising the interface’s IP address with a cost of 0.
3. When flooding out a non-broadcast interface (when either in NBMA or Point-to-
MultiPoint mode) the Link State Update or Link State Acknowledgment packet must be
replicated in order to be sent to each of the interface’s neighbors.
The following is an example of point-to-multipoint configuration on a NBMA (Frame Relay in this
case) network. Attached is the resulting routing table and Router Link state along with other
pertinent information:
interface Ethernet0
ip address 130.10.6.1 255.255.255.0
!
interface Serial0
no ip address
encapsulation frame-relay
frame-relay lmi-type ansi
!
interface Serial0.1 multipoint
ip address 130.10.10.3 255.255.255.0
ip ospf network point-to-multipoint
ip ospf priority 10
frame-relay map ip 130.10.10.1 140 broadcast
frame-relay map ip 130.10.10.2 150 broadcast
!
router ospf 2
network 130.10.10.0 0.0.0.255 area 0
network 130.10.6.0 0.0.0.255 area 1
R6#sh ip ospf int s 0.1
Serial0.1 is up, line protocol is up
Internet Address 130.10.10.3/24, Area 0
Process ID 2, Router ID 140.10.1.1, Network Type POINT_TO_MULTIPOINT, Cost: 6,
Timer intervals configured, Hello 30, Dead 120, Wait 120, Retransmit 5
Hello due in 00:00:18
Neighbor Count is 2, Adjacent neighbor count is 2
Adjacent with neighbor 130.10.10.2
Adjacent with neighbor 130.10.5.129
R6#sh ip ospf ne
Neighbor ID PriStateDead Time Address Interface
130.10.10.20FULL/ 00:01:37130.10.10.2 Serial0.1
130.10.5.129 0FULL/ -00:01:53 130.10.10.1 Serial0.1
R6#
R6#sh ip ro
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route
Gateway of last resort is not set
130.10.0.0/16 is variably subnetted, 9 subnets, 3 masks
O130.10.10.2/32 [110/64] via 130.10.10.2, 00:03:28, Serial0.1
C130.10.10.0/24 is directly connected, Serial0.1
O130.10.10.1/32 [110/64] via 130.10.10.1, 00:03:28, Serial0.1
O IA130.10.0.0/22 [110/74] via 130.10.10.1, 00:03:28, Serial0.1
O130.10.4.0/24 [110/74] via 130.10.10.2, 00:03:28, Serial0.1
C130.10.6.0/24 is directly connected, Ethernet0
R6#sh ip ospf data router 140.10.1.1
OSPF Router with ID (140.10.1.1) (Process ID 2)
Router Link States (Area 0)
LS age: 806
Options: (No TOS-capability)
LS Type: Router Links
Link State ID: 140.10.1.1
Advertising Router: 140.10.1.1
LS Seq Number: 80000009
Checksum: 0x42C1
Length: 60
Area Border Router
Number of Links: 3
Link connected to: another Router (point-to-point)
(Link ID) Neighboring Router ID: 130.10.10.2
(Link Data) Router Interface address: 130.10.10.3
Number of TOS metrics: 0
TOS 0 Metrics: 64
Link connected to: another Router (point-to-point)
(Link ID) Neighboring Router ID: 130.10.5.129
(Link Data) Router Interface address: 130.10.10.3
Number of TOS metrics: 0
TOS 0 Metrics: 64
Link connected to: a Stub Network
(Link ID) Network/subnet number: 130.10.10.3
(Link Data) Network Mask: 255.255.255.255
Number of TOS metrics: 0
TOS 0 Metrics: 0
