What is ospf area

In order to create the virtual link, configure the area 5 virtual-link 2. Skip to content Skip to search Skip to footer. Available Languages. Download Options.

Updated: February 25, Contents Introduction. Each OSPF network that is divided into different areas must follow these rules: A backbone area - which combines a set of independent areas into a single domain - must exist. Define a Stub Area Use the area xx stub command in every router in the area to define an area as a stub area.

What Are Virtual Links? In this example, the virtual link connects area 7 to the backbone through area 5: In this example, the virtual link is created between the routers with router ID 1. Contributed by Cisco Engineers. Was this Document Helpful? Yes No Feedback. Related Cisco Community Discussions. Jeremy you did an excellent and lucid presentation of the most important element of OSPF. Thank You!!! You explain the topic on stub areas very clear, for us newbies like me.

Thank you very much. Very nice article, kudos for the good work. I find little difficult to understand NSSA. I think the diagram must is using area 0 to show as NSSA because the arrows are showing converting the type 7 to type 5 LSA from right to left. Seems little confusing to me. I can only attest that to this day, this system is probably one of the most confusing naming conventions that has ever been made up by a technology vendor. Very good writing-up, as always. I learned a lot form your articles.

Thanks a lot for your hard work. Have you been looking for a better way to model your network infrastructure?

Check out what we're doing with NetBox! Open source and widely extensible, NetBox has enabled thousands of organizations to automate their networks like never before possible. Whether the other types of LSAs are advertised within an area depends on the area type, and there are many: Backbone area area 0 Standard area Stub area Totally stubby area Not-so-stubby area NSSA Let's begin by examining a standard area.

Standard Areas In the example above, router 2 acts as the area border router ABR between a standard area and the backbone. Stub Areas In this next example, R2 and R3 share a common stub area. Router config-router area 10 stub This idea of substituting a single default route for many specific routes can be applied to internal routes as well, which is the case of totally stubby areas. A stub area is extended to a totally stubby area by configuring all of its ABRs with the no-summary parameter: Router config-router area 10 stub no-summary Stub and totally stubby areas can certainly be convenient to reduce the resource utilization of routers in portions of the network not requiring full routing knowledge.

Router config-router area 10 nssa default-information-originate To expand an NSSA to function as a totally stubby area, eliminating type 3 LSAs, all of its ABRs must be configured with the no-summary parameter: Router config-router area 10 nssa no-summary The ABR of a totally stubby NSSA or not-so-totally-stubby area, if you prefer injects a default route without any further configuration.

The backbone is considered a standard area. Stub areas can contain type 1, 2, and 3 LSAs. A default route is substituted for external routes. The type 3 LSA describes a default route, substituted for all external and inter-area routes. Posted in Routing. Support PacketLife by buying stuff you don't need! Kevin Gillick June 24, at p. Ed June 24, at p. Matt June 25, at a. Adam June 25, at p.

Hesham July 7, at a. Michael November 14, at a. Jairo December 11, at a. Farhan Araj January 5, at a. Sumit Mittal January 8, at a.

Ibrahim April 20, at a. Very simple, very clear! Really best document I've seen. Many thanks.. Pras June 26, at a. Is type 4 LSA allowed in Stub areas? In the Summary only types 1, 2 and 3 are mentioned under 'Stub Area'. Sarabjeet July 3, at p. Andy August 30, at a. Mahen September 11, at a. Thomboy October 3, at p. Ramesh January 4, at a. Ismail March 31, at a. Fuzz October 22, at a. A guest December 6, at p.

BlueRose December 30, at p. BlueRose January 9, at a. Dear Stretch, Thanks a Lot Your article help me a lot. Regards, Rain. Sandesh February 8, at a. Hi Stretch, I appreciate your effort on this one.

Thank you, -Sandesh. Real good article!!! Shweta September 17, at p. What is DPDK? What is BFD? Network Automation - The What and the Why? What is Idempotency? Here's a Small Trick! Master Network Automation. Standard Area — a nonbackbone area that must be connected to the backbone area; it accepts intra-area, inter-area, external and a default route. Stub Area — has a single exit point ABR ; typically used in hub-and-spoke network; accepts intra-area routes but does not accept external summary routes from non-OSPF sources; implies using a default route to send packets to an external network.

Totally Stubby Area — Cisco proprietary; does not accept external AS routes or inter-area routes; recognizes only intra-area routes and the default route. NSSA — recognizes intra-area, inter-area routes and the default route 0. Refer to the following figure to understand OSPF area types:.

You may as well find the following mental map useful crossed marks are not recognized in the area :. Dividing your network into areas limits the impact of a topology change within an area and minimizes routing table entries, and thereby improves the performance of your network. Even if your network is small and there is no need to divide it in multiple areas momentarily, you should bear this in mind.

Namely, even small networks have a tendency to grow, and you should consider implementing areas for possible future expansions. Also, if you want to control the advertisement of inter-area and external routes into an area, you should definitely consider implementing one of the OSPF special areas stub, stubby, NSSA, totally stubby NSSA , depending on your needs. It is recommended that an area has no more than 50 routers, and that a router is not a part of more than three areas.