Configuring OSPF Attributes on Different Types of Networks
Applicable Environment
By setting network types for OSPF interfaces and adjusting OSPF attributes, you can flexibly build OSPF networks.
In Table 5-19, OSPF classifies networks into four types based on the types of link layer protocols.
Network Type |
Characteristic |
Default Configuration |
|---|---|---|
Broadcast |
On a 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. An NBMA network must be fully meshed. Any two switches on an 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 its link layer protocol. A P2MP network must be forcibly changed from the network of another type. |
As described in Table 5-19, the difference between OSPF configurations on networks of different types lies in the packet transmission mode.
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