OSPF Features, Advantages, Disadvantages

This tutorial compares OSPF and RIP routing protocols and lists the features of OSPF. Learn the advantages and disadvantages of the OSPF routing protocol.

OSPF stands for Open Shortest Path First. It is an open standard routing protocol. It has three versions: OSPFv1, OSPFv2, and OSPFv3. OSPFv1 was developed in the mid-1980s to overcome the limitations, deficiencies, and scalability problems that RIP had in large networks. In 1998, OSPFv1 was updated by OSPFv2 to support modern infrastructure and networks. OSPFv1 is not used in modern networks. Similarly, to support modern infrastructure, RIP was also updated by RIPv2.

The following table compares the features of OSPFv2, RIP, and RIPv2.

Feature OSPFv2 RIPv1 RIPv2
Protocol type Link state Distance vector Distance vector
Algorithm Dijkstra Bellman ford Bellman ford
Metric Bandwidth Hops Hops
Hop count limit None 15 15
VLSM support Yes No Yes
Classless support Yes No Yes
Non-contiguous network support Yes No Yes
Auto-summarization No Yes Yes
Manual summarization Yes No Yes
Route propagation Multicast Broadcast Broadcast
Convergence Fast Slow Slow
Use authentication Yes No Yes
Update On event periodic periodic
Supported network type All types Flat only Flat only

Since OSPFv2 includes all features and characteristics that modern networks need, it is one of the two most popular and widely used routing protocols. It was developed when IPv6 was not in use. Because of this, support for IPv6 was not added to OSPFv2.

To support IPv6, instead of updating the OSPFv2, developers developed a new version of OSPF. It was OSPFv3. It was released in 2008. The following table compares the features of OSPFv2 and OSPFv3.

It supports IPv4. It supports IPv6.
It is specified in RFC2328. It is specified in RFC 5340.
The header size is 24 bytes. The header size is 16 bytes.
It uses seven link-state advertisements. It uses nine link-state advertainments. Two new included LSA are link-LSA and intra-area-prefix-LSA.
You can run only one instance per link. You can run many instances per link.
It needs a network mask to form an adjacency. It does not need a network mask to form an adjacency.
It uses MD5 hashing for authentication. It uses IPSec for authentication.
It uses networks. It uses links.
It can configure its RID automatically. It can't configure its own RID. You have to configure RID manually.

Since OSPFv1 has been updated and replaced by OSPFv2, network administrators commonly use the term OSPF to refer to OSPFv2. Because of this, unless the version of OSPF is explicitly mentioned, you can consider all references to OSPF to be OSPFv2.

Advantages of OSPF

  • It is based on an open standard. It can run on most routers.
  • It uses the SPF algorithm to provide a loop-free topology.
  • It uses both trigger updates and incremental updates to provide fast convergence.
  • It supports VLSM and route summarization for a hierarchical design.
  • It supports both versions of IP protocol. OSPFv2 supports IPv4 and OSPFv3 supports IPv6.
  • It supports load balancing with equal-cost routes for the same destination.
  • It supports networks of all sizes.

Disadvantages OSPF

  • It needs lots of information to calculate the best route for each destination. To store this information, OSPF consumes more memory than other routing protocols.
  • To calculate the best route, it runs the SPF algorithm that requires extra CPU processing.
  • It is complex to configure and difficult to troubleshoot. In a large network, only experienced network administrators can configure it.

Usages of OSPF

Typically, OSPF is used in large enterprise networks that use routing equipment from different vendors. OSPF is also used in companies that have the policy to use an open standard protocol for routing which gives them flexibility when they need to replace an existing router or add a new router.

It is recommended to use an advanced routing protocol if you have more than 50 routers in your network. Currently, there are only two advanced routing protocols in use that can scale any size of the network. These protocols are EIGRP and OSPF. EIGRP is a Cisco proprietary protocol. It means if you want to use EIGRP, you have to use only Cisco routers in your network. If you have a non-Cisco router in your network, EIGRP will not work on it. In such a situation, you can use OSPF. Basically, in a mixed vendor environment, OSPF is the only choice we have for routing.

Key features of OSFP

  • OSPF is an interior gateway protocol (IGP).
  • It runs within a single routing domain, such as an autonomous system (AS).
  • It uses a concept called areas, to optimize network traffic and simplify administration.
  • It uses Dijkstra's algorithm to compute the shortest route to each destination.
  • It runs over IP protocol but does not use a transport protocol (such as TCP or UDP) to encapsulate its data.
  • It encapsulates its data directly in IP packets with protocol number 89.
  • It uses its own error detection and correction mechanism.
That’s all for this tutorial. In this tutorial, we discussed the features, advantages, and disadvantages of OSPF.

ComputerNetworkingNotes CCNA Study Guide OSPF Features, Advantages, Disadvantages