Short for Open Shortest Path First,
a routing protocol developed for IP networks based on the shortest path first or link-state algorithm.
Routers use link-state algorithms to send routing information to all nodes in an Internetwork
by calculating the shortest path to each node based on topography of the Internet constructed by each node. Each router sends
that portion of the routing table (keeps track of routes to particular network destinations) that describes the state of its
own links, and it also sends the complete routing structure (topography).
The advantage of shortest path first algorithms
is that they result in smaller more frequent updates everywhere. They converge quickly, thus preventing such problems as routing
loops and Count-to-Infinity (when routers continuously increment the hop count to a particular network). This makes for a stable network.
The disadvantage of shortest path
first algorithms is that they require a lot of CPU power and memory. In the end, the advantages out weigh the disadvantages.
OSPF Version 2 is defined in RFC 1583. It is rapidly replacing RIP on the Internet.
If you want to know
more about OSPF, you can visit the links that I've given.
OSPF Home Page:
In this page you can find all the
information to implement this routing protocol. It gives links to various RFCs that are required for implementing it. If you
are new to OSPF, this is not the starting point. I recommend go thru some tutorials.
This site gives good introduction to OSPF Version 2. This is
latest version of OSPF.
That is the question: should you use the older, more established RIP (Routing
Information Protocol) or the new-kid-on-the-block OSPF (Open Shortest Path First) IGP (Interior Gateway Protocol)? This article
can help you make the right decision--it describes the pro's and con's for using either protocol and provides some specific
If you want to want to learn practically
about OSPF, you can make your linux PC to a OSPF (RIP/BGP) router. Here is the more information about the free routing software
GNU Zebra is free software (distributed under GNU Generic Public License) that manages TCP/IP based routing
protocols. It supports BGP-4 protocol as described in RFC1771 (A Border Gateway Protocol 4) as well as RIPv1, RIPv2 and OSPFv2. Unlike traditional,
Gated based, monolithic architectures and even the so-called "new modular architectures" that remove the burden of processing
routing functions from the cpu and utilize special ASIC chips instead, Zebra software offers true modularity.
best way to learn OSPF is system testing it. I am giving link to the OSPF testing suits, which describes how to test OSPF
and also gives test plans. The test plan becomes your guide to learn OSPF behavior under various conditions.
OSPF Test Suits:
This test suit is not for free. But it is very good one. This test suit is
called ANVL. This can simulate number of routers in number of complex topologies. These topologies are very useful for testing
OSPF protocol. Here is what they say about ANVL.
OSPF (Open Shortest Path First) is a link-state routing protocol intended to support large
numbers of subnetworks within a single Autonomous System. ANVL's automated conformance test product allows network equipment
manufacturers to verify their device's compliance to the OSPF standard.
This test suite includes over 300 tests based on RFC 1583 and RFC 2328. Network equipment
manufacturers can use ANVL to quickly determine OSPF implementation errors by running ANVL's high log level (pass/fail). More
detailed results (including packet decodes) can also be viewed by running the test suite's medium and low log levels.
Open Shortest Path First IGP (ospf) Charter (Links to Draft and
to OSPF (mospf) Charter. ( links to drafts and RFC)
Research paper describing
OSPF usage and functionality
OSPF: Frequently Asked Questions