Configuring OSPF network types

OSPF classifies networks into the following types based on the link layer protocol:

• Broadcast—When the link layer protocol is Ethernet or FDDI, OSPF classifies the network type as broadcast by default.

• NBMA—When the link layer protocol is Frame Relay, ATM, or X.25, OSPF classifies the network type as NBMA by default.

• P2P—When the link layer protocol is PPP, LAPB, or HDLC, OSPF classifies the network type as P2P by default.

When you change the network type of an interface, follow these guidelines:

• When an NBMA network becomes fully meshed, change the network type to broadcast to avoid manual configuration of neighbors.

• If any routers in a broadcast network do not support multicasting, change the network type to NBMA.

• An NBMA network must be fully meshed. OSPF requires that an NBMA network be fully meshed. If a network is partially meshed, change the network type to P2MP.

• If a router on an NBMA network has only one neighbor, you can change the network type to P2P to save costs.

Two broadcast-, NBMA-, and P2MP-interfaces can establish a neighbor relationship only when they are on the same network segment.