Jul
23
2013

When to use OSPF | why use Open shortest path first?

Why we use OSPF as a Routing Protocol?

OSPF works great in different WAN environments like  point to point, non broad cost multi-access, point to multipoint, frame-relay and in LAN environment. OSPF is also a great routing protocol for dialup scenarios and in heterogeneous organization which use to own different companies or business having with different vendors’ devices. In such environments OSPF is better choice because of it flexibility and following great features.

OSPF Open shortest path first

  •  Open shortest path first is design for replacement of RIP and support large and most complex networks. The most recent version of OSPF is version 3 that is defined is RFC 2740, which also have the IPv6 support. OSPF is open standard protocol, you can run OSPF among any vender.
  • OSPF has fast convergence and also have the option for tuning more metric values. OSPF support VLSM and is a better protocol for dialup.
  • In OSPF you can divide your network into different OSPF areas. The central or core area is known as backbone area and all other area must be connect to this backbone area. The idea behind the OSPF areas is to lower the amount of routing traffic and lower the processing of your core routers. Different areas are connected with each other through Area Border Router (ABR).
  • OSPF is link state routing protocol and you can tune a link state routing protocol to converge fast. Link state routing protocols send the periodic update via LSAs you can learn more about OSPF LSAs.
  • Metric is “OSPF cost” (based on interface bandwidth by default).
  • Default administrative distance for OSPF is 110.
  • With Cisco routers, OSPF also supports equal-cost multipath load balancing and neighbor authentication.
  • OSPF find the shortest path among the different areas using the dijkstra algorithm, ABR of each router calculate the roadmap/shortest path to each destination and send the only summary route to backbone.
  •  OSPF also offer the special area types like stub area, totally stub area and not so stubby area (NSSA). Using these area types you can minimize the LSAs in an area and also decide that which routing information should be injected into backbone or which are not.

Learn How to configure OSPF in packet tracer.

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