|
|
OSPF has two new features related to point-to-multipoint networks. One feature applies to broadcast networks; the other feature applies to nonbroadcast networks.
Before this feature, some OSPF point-to-multipoint protocol traffic was treated as multicast traffic. Therefore, the neighbor command was not needed for point-to-multipoint interfaces because multicast took care of the traffic. Hellos, updates and acknowledgments were sent using multicast. In particular, multicast hellos discovered all neighbors dynamically.
However, some customers were using point-to-multipoint on nonbroadcast media (such as classic IP over ATM), so their routers could not dynamically discover their neighbors. This feature allows the neighbor command to be used on point-to-multipoint interfaces.
On any point-to-multipoint interface (broadcast or not), the Cisco IOS software assumed the cost to each neighbor was equal. The cost was configured with the ip ospf cost command. In reality, the bandwidth to each neighbor is different, so the cost should be different. With this feature, you can configure a separate cost to each neighbor. This feature applies to point-to-multipoint interfaces only.
You can now configure neighbors on point-to-multipoint interfaces and assign a cost to each neighbor. These capabilities allow the router to dynamically discover neighbors over nonbroadcast media and to prefer some routes over others by assigning different costs to neighbors.
This feature is supported on these platforms:
This section describes the following tasks to configure OSPF point-to-multipoint interfaces. Perform one of these tasks, depending on whether your network is broadcast or nonbroadcast.
To treat an interface as point-to-multipoint broadcast and assign a cost to each neighbor, perform the following tasks beginning in interface configuration mode:
| Task | Command |
|---|---|
Step 1 Configure an interface as point-to-multipoint for broadcast media. | |
Step 2 Enter global configuration mode. | exit |
Step 3 Configure an OSPF routing process and enter router configuration mode. | router ospf process-id |
Step 4 Specify a neighbor and assign a cost to the neighbor. | neighbor ip-address cost number |
Step 5 Repeat Step 4 for each neighbor if you want to specify a cost. Otherwise, neighbors will assume the cost of the interface, based on the ip ospf cost command. |
|
To treat the interface as point-to-multipoint when the media does not support broadcast, perform the following task in interface configuration mode:
| Task | Command |
|---|---|
Step 1 Configure an interface as point-to-multipoint for nonbroadcast media. | |
Step 2 Enter global configuration mode. | exit |
Step 3 Configure an OSPF routing process and enter router configuration mode. | router ospf process-id |
Step 4 Specify an OSPF neighbor and optionally assign a cost to the neighbor. | neighbor ip-address [cost number] |
Step 5 Repeat Step 4 for each neighbor. |
|
This section includes the following configuration examples:
The following example illustrates a point-to-multipoint network with broadcast.
interface Serial0 ip address 10.0.1.1 255.255.255.0 encapsulation frame-relay ip ospf cost 100 ip ospf network point-to-multipoint frame-relay map ip 10.0.1.3 202 broadcast frame-relay map ip 10.0.1.4 203 broadcast frame-relay map ip 10.0.1.5 204 broadcast frame-relay local-dlci 200 ! router ospf 1 network 10.0.1.0 0.0.0.255 area 0 neighbor 10.0.1.5 cost 5 neighbor 10.0.1.4 cost 10
The configuration of the neighbor at 10.0.1.3 is:
interface $core2s2 ip address 10.0.1.3 255.255.255.0 ip ospf network point-to-multipoint encapsulation frame-relay frame-relay local-dlci 301 frame-relay map ip $core7s0_ip 300 broadcast no shut ! router ospf 1 network 10.0.1.0 0.0.0.255 area 0
The output shown for neighbors in the first configuration above looks like this:
Router# show ip ospf neighbor Neighbor ID Pri State Dead Time Address Interface 4.1.1.1 1 FULL/ - 00:01:50 10.0.1.5 Serial0 3.1.1.1 1 FULL/ - 00:01:47 10.0.1.4 Serial0 2.1.1.1 1 FULL/ - 00:01:45 10.0.1.3 Serial0
The route information in the first configuration above looks like this:
Router# show ip route
Codes: C - connected, S - static, I - IGRP, 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, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
Gateway of last resort is not set
C 1.0.0.0/8 is directly connected, Loopback0
10.0.0.0/8 is variably subnetted, 4 subnets, 2 masks
O 10.0.1.3/32 [110/100] via 10.0.1.3, 00:39:08, Serial0
C 10.0.1.0/24 is directly connected, Serial0
O 10.0.1.5/32 [110/5] via 10.0.1.5, 00:39:08, Serial0
O 10.0.1.4/32 [110/10] via 10.0.1.4, 00:39:08, Serial0
The following example illustrates a point-to-multipoint network with nonbroadcast.
interface Serial0 ip address 10.0.1.1 255.255.255.0 ip ospf network point-to-multipoint non-broadcast encapsulation frame-relay no keepalive frame-relay local-dlci 200 frame-relay map ip 10.0.1.3 202 frame-relay map ip 10.0.1.4 203 frame-relay map ip 10.0.1.5 204 no shut ! router ospf 1 network 10.0.1.0 0.0.0.255 area 0 neighbor 10.0.1.3 cost 5 neighbor 10.0.1.4 cost 10 neighbor 10.0.1.5 cost 15
The following is the configuration for the router on the other side:
interface Serial9/2 ip address 10.0.1.3 255.255.255.0 encapsulation frame-relay ip ospf network point-to-multipoint non-broadcast no ip mroute-cache no keepalive no fair-queue frame-relay local-dlci 301 frame-relay map ip 10.0.1.1 300 no shut ! router ospf 1 network 10.0.1.0 0.0.0.255 area 0
The output shown for neighbors in the first configuration above looks like this:
Router# show ip ospf neighbor Neighbor ID Pri State Dead Time Address Interface 4.1.1.1 1 FULL/ - 00:01:52 10.0.1.5 Serial0 3.1.1.1 1 FULL/ - 00:01:52 10.0.1.4 Serial0 2.1.1.1 1 FULL/ - 00:01:52 10.0.1.3 Serial0
This section documents modified commands. All other commands used with this feature are documented in the Cisco IOS Release 11.3 command references.
broadcast | Sets the network type to broadcast. |
non-broadcast | Sets the network type to NBMA. |
point-to-multipoint [non-broadcast] | Sets the network type to point-to-multipoint. |
Depends on the network type.
Interface configuration
This command first appeared in Cisco IOS Release 10.0. The point-to-multipoint keyword first appeared in Cisco IOS Release 10.3. The non-broadcast keyword used with the point-to-multipoint keyword first appeared in Cisco IOS Release 11.3 AA.
Using this feature, you can configure broadcast networks as nonbroadcast multiaccess (NBMA) networks when, for example, you have routers in your network that do not support multicast addressing. You can also configure nonbroadcast multiaccess networks (such as X.25, Frame Relay, and SMDS) as broadcast networks. This feature saves you from having to configure neighbors.
Configuring NBMA networks as either broadcast or nonbroadcast assumes that there are virtual circuits from every router to every router or fully meshed network. This is not true for some cases, for example, because of cost constraints or when you have only a partially meshed network. In these cases, you can configure the OSPF network type as a point-to-multipoint network. Routing between two routers that are not directly connected will go through the router that has virtual circuits to both routers. You do not need to configure neighbors when using this feature.
If this command is issued on an interface that does not allow it, it will be ignored.
OSPF has two features related to point-to-multipoint networks. One feature applies to broadcast networks; the other feature applies to nonbroadcast networks.
The following example sets your OSPF network as a broadcast network:
interface serial 0
ip address 160.89.77.17 255.255.255.0 ip ospf network broadcast encapsulation frame-relay
The following example illustrates a point-to-multipoint network with broadcast.
interface Serial0 ip address 10.0.1.1 255.255.255.0 encapsulation frame-relay ip ospf cost 100 ip ospf network point-to-multipoint frame-relay map ip 10.0.1.3 202 broadcast frame-relay map ip 10.0.1.4 203 broadcast frame-relay map ip 10.0.1.5 204 broadcast frame-relay local-dlci 200 ! router ospf 1 network 10.0.1.0 0.0.0.255 area 0 neighbor 10.0.1.5 cost 5 neighbor 10.0.1.4 cost 10
frame-relay map
neighbor (OSPF)
x25 map
ip-address | Interface IP address of the neighbor. |
priority number | (Optional) 8-bit number indicating the router priority value of the nonbroadcast neighbor associated with the IP address specified. The default is 0. This keyword does not apply to point-to-multipoint interfaces. |
poll-interval seconds | (Optional) Unsigned integer value reflecting the poll interval. RFC 1247 recommends that this value be much larger than the hello interval. The default is 120 seconds (2 minutes). This keyword does not apply to point-to-multipoint interfaces. |
cost number | (Optional) Assigns a cost to the neighbor, in the form of an integer from 1 to 65535. Neighbors with no specific cost configured will assume the cost of the interface, based on the ip ospf cost command. On point-to-multipoint interfaces, this is the only keyword and argument that make sense. This keyword does not apply to NBMA networks. |
No configuration is specified.
Router configuration
This command first appeared in Cisco IOS Release 10.0. The cost keyword was added in Release 11.3 AA.
X.25 and Frame Relay provide an optional broadcast capability that can be configured in the map to allow OSPF to run as a broadcast network. At the OSPF level you can configure the router as a broadcast network. See the x25 map and frame-relay map commands in the "X.25 Commands" and "Frame Relay Commands" chapters, respectively, in the Wide-Area Networking Command Reference for more detail.
One neighbor entry must be included in the Cisco IOS software configuration for each known nonbroadcast network neighbor. The neighbor address has to be on the primary address of the interface.
If a neighboring router has become inactive (hello packets have not been seen for the Router Dead Interval period), it may still be necessary to send hello packets to the dead neighbor. These hello packets will be sent at a reduced rate called Poll Interval.
When the router first starts up, it sends only hello packets to those routers with non-zero priority; that is, routers that are eligible to become designated routers (DR) and backup designated routers (BDR). After DR and BDR are selected, DR and BDR will then start sending hello packets to all neighbors in order to form adjacencies.
Prior to Release 12.0, the neighbor command applied to NBMA networks only. With Release 12.0, the neighbor command applies to NBMA networks and point-to-multipoint networks. On NBMA networks, the cost keyword is not accepted.
The following example declares a router at address 131.108.3.4 on a nonbroadcast network, with a priority of 1 and a poll interval of 180 seconds:
router ospf
neighbor 131.108.3.4 priority 1 poll-interval 180
The following example illustrates a point-to-multipoint network with nonbroadcast.
interface Serial0 ip address 10.0.1.1 255.255.255.0 ip ospf network point-to-multipoint non-broadcast encapsulation frame-relay no keepalive frame-relay local-dlci 200 frame-relay map ip 10.0.1.3 202 frame-relay map ip 10.0.1.4 203 frame-relay map ip 10.0.1.5 204 no shut ! router ospf 1 network 10.0.1.0 0.0.0.255 area 0 neighbor 10.0.1.3 cost 5 neighbor 10.0.1.4 cost 10 neighbor 10.0.1.5 cost 15
ip ospf network
ip ospf priority
Posted: Fri Mar 12 23:18:56 PST 1999
Copyright 1989-1999©Cisco Systems Inc.