Configuring OSPF on the NBMA or P2MP Network

This section describes how to configure OSPF and modify attributes on the NBMA or point-to-multipoint (P2MP) network to flexibly construct the OSPF network.

Applicable Environment

As shown in Table 1, OSPF classifies networks into four types based on the types of link layer protocols.

Differentiated OSPF configurations that are applicable to the NBMA network and P2MP network are provided in this section. The OSPF configurations not provided here are applicable to the four types of networks.

**Table 1** Network types supported by OSPF
Network Type	Characteristic	Default Configuration
Broadcast	On the broadcast network, Hello packets, LSU packets, and LSAck packets are multicast; DD packets and LSR packets are unicast.	If the link layer protocol is Ethernet or Fiber Distributed Data Interface (FDDI), OSPF regards the network as a broadcast network by default.
Non-broadcast multiple access (NBMA)	On an NBMA network, Hello packets, DD packets, LSR packets, LSU packets, and LSAck packets are unicasted. The NBMA network must be fully meshed. Any two routers on the NBMA network must be directly reachable.	-
Point-to-point (P2P)	On a P2P network, Hello packets, DD packets, LSR packets, LSU packets, and LSAck packets are multicasted.	If the link layer protocol is Link Access Procedure Balanced (LAPB), OSPF regards the network as a P2P network by default.
Point-to-multipoint (P2MP)	On a P2MP network, Hello packets are multicasted; DD packets, LSR packets, LSU packets, and LSAck packets are unicasted. The mask lengths of the routers on the P2MP network must be the same.	OSPF does not regard a network as a P2MP network by default regardless of any link layer protocol. A P2MP network is forcibly changed from the network of another type.

As shown in Table 1, OSPF sends packets in different manners on networks of different types. Therefore, the difference between OSPF configurations on the networks lies in the packet sending configurations.

Pre-configuration Tasks

Before configuring session parameters for the OSPF neighbor or adjacency relationship, complete the following tasks:

Configuring a link layer protocol
Configuring IP addresses for interfaces to ensure that neighboring nodes are reachable at the network layer
Configuring Basic OSPF Functions

Configuring Network Types for OSPF Interfaces: OSPF classifies networks into four types based on the types of link layer protocols. You can configure the network type for an OSPF interface to forcibly change its original network type.

Configuring NBMA Network Attributes: To implement OSPF functions, configure NBMA network attributes.

Configuring P2MP Network Attributes: To implement OSPF functions, configure P2MP network attributes.

Verifying the Configuration of OSPF on the NBMA or P2MP Network: After OSPF attributes are set on networks of different types, you can check OSPF neighbor and interface information.