Open Shortest Path First (OSPF)

Open Shortest Path First (OSPF)

This section describes OSPF routing.

The following topics are included in this section: OSPF Background and concepts

Troubleshooting OSPF Basic OSPF example

Advanced inter-area OSPF example

Controlling redundant links by cost


OSPF Background and concepts

OSPF (Open Shortest Path First) is a link-state interior routing protocol, that is widely used in large enterprise organizations. It only routes packets within a single autonomous system (AS). This is different from BGP as BGP can communicate between ASes.

This section includes:

  • Background
  • The parts and terminology of OSPF
  • How OSPF works


OSPF version 2 was defined in 1998 in RFC 2328. OSPF was designed to support classless IP addressing, and variable subnet masks. This was a shortcoming of the earlier RIP protocols.

Updates to OSPF version 2 are included in OSPF version 3 defined in 2008 in RFC 5340. OSPF3 includes support for IPv6 addressing where previously OSPF2 only supports IPv4 addressing.

The main benefit of OSPF is that it detects link failures in the network quickly and within seconds has converged network traffic successfully without any networking loops. Also OSPF has many features to control which routes are propagated and which are not, maintaining smaller routing tables. OSPF can also provide better load- balancing on external links than other interior routing protocols.

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