Cisco Systems 78-11741-02 manual Configuring Point-to-Multipoint, Broadcast Networks, IPC-227

Configuring OSPF

Configuring OSPF over Different Physical Networks

To configure your OSPF network type, use the following command in interface configuration mode:

Command	Purpose
Router(config-if)#ip ospf network {broadcast	Configures the OSPF network type for a specified interface.
non-broadcast {point-to-multipoint
[non-broadcast] point-to-point}}

See the “OSPF Point-to-Multipoint Example” section at the end of this chapter for an example of an OSPF point-to-multipoint network.

Configuring Point-to-Multipoint, Broadcast Networks

On point-to-multipoint, broadcast networks, there is no need to specify neighbors. However, you can specify neighbors with the neighbor router configuration command, in which case you should specify a cost to that neighbor.

Before the point-to-multipointkeyword was added to the ip ospf network interface configuration command, some OSPF point-to-multipoint protocol traffic was treated as multicast traffic. Therefore, the neighbor router configuration command was not needed for point-to-multipoint interfaces because multicast took care of the traffic. Hello, update, and acknowledgment messages were sent using multicast. In particular, multicast hello messages discovered all neighbors dynamically.

On any point-to-multipoint interface (broadcast or not), the Cisco IOS software assumed that the cost to each neighbor was equal. The cost was configured with the ip ospf cost interface confutation command. In reality, the bandwidth to each neighbor is different, so the cost should differ. With this feature, you can configure a separate cost to each neighbor. This feature applies to point-to-multipoint interfaces only.

To treat an interface as point-to-multipoint broadcast and assign a cost to each neighbor, use the following commands beginning in interface configuration mode:

	Command	Purpose
Step 1
	Router(config-if)# ip ospf network	Configures an interface as point-to-multipoint for
	point-to-multipoint	broadcast media.
Step 2
	Router(config-if)# exit	Enters global configuration mode.
Step 3
	Router(config)# router ospf process-id	Configures an OSPF routing process and enters router
		configuration mode.
Step 4
	Router(config-router)# neighbor ip-addresscost	Specifies a neighbor and assigns a cost to the
	number	neighbor.

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 interface configuration command.

Configuring OSPF for Nonbroadcast Networks

Because many routers might be attached to an OSPF network, a designated router is selected for the network. Special configuration parameters are needed in the designated router selection if broadcast capability is not configured.

Cisco IOS IP Configuration Guide

IPC-227