Open Shortest Path First (OSPF)

Open Shortest Path First (OSPF) is a link-state routing protocol replacing distance vector routing protocol, RIP. RIP was acceptable in the early days of networking. RIP uses hop count as the metric which is not working better in the larger network. Open Shortest Path First (OSPF) has many advantages over RIP. It can scale a larger network and offer a faster convergence. It is a classless routing protocol using the concept of areas for scaling the network. OSPF uses the Dijkstra algorithm created a famous programmer Edsger Wybe Dijkstra.

Development of OSPF

The Internet Engineering Task Force (IETF) starts initial working on OSPF in 1987. Meanwhile, the internet was not public; it only used as an academic and research network funded by the government of United status.  In 1989 the OSPF version 1 specification was published in RFC 1131; only for running on routers and UNIX workstations. Later its implementation became a widespread UNIX process known as GATED. Version 1 of the OSPF is an experimental routing protocol and was never deployed.  In 1991, John Moy introduced OSPF version 2 in RFC 1247. Version 2 gives significant improvements over version 1. It is classless and supporting VLSM and CIDR. It the same time the IETF chose OSPF as their recommended interior gateway protocol(IGP)

In 1998, version 2 was updated in RFC 2328; which remains the current RFC for OSPF. In 1999, OSPF version 3 was introduced in RFC 2740. It was created by John Moy, Rob Count; and Dennis for IPv6. In 2008, OSPFv3 has updated in RFC 5340 as OSPF for IPv6.

Features of OSPF

The Open Shortest Path First (OSPF) has many features included:

  • Classless– OSPF is classless by design, so, it supports VLSM and CIDR.
  • Fast convergence– it is fast convergence and quickly propagates network changes.
  • Efficient– OSPF has no periodic update, it only triggers routing updates on the event. It uses the SPF algorithm to choose the best path.
  • Scalable– It works well both in small and large networks. We can group the routers into areas to support a hierarchical system.
  • Secure– OSPF supports MD5 (Message Digest 5) authentication. When MD5 has enabled, routers only accept encrypted routing updates from peers with the same pre-shared password.
  • Trustworthiness – Administrative distance is the trustworthiness of the route source. OSPF has a default administrative distance of 110 and preferred over IS-IS and RIP.
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