Configuring OSPF Attributes in Different Types of Networks
By setting network types for OSPF interfaces and adjusting OSPF attributes, you can flexibly build OSPF networks.
Applicable Environment
In Table 5-21, OSPF classifies networks into four types based on the type of link layer protocols.
Differentiated OSPF configurations that are applicable only to NBMA networks and P2MP networks are provided in this section. The OSPF configurations not provided here are applicable to the four types of networks.
Network Type |
Characteristic |
Default Configuration |
|---|---|---|
Broadcast |
On the broadcast network, Hello packets, LSU packets, and LSAck packets are multicasted; DD packets and LSR packets are unicasted. |
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. |
If the link layer protocol is ATM, OSPF regards the network as an NBMA network by default. |
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 PPP, HDLC, or 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. |
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 described in Table 5-21, the difference between OSPF configurations on networks of different types lies in the packet transmission mode.
