Protocols that Use Link-State

There are only two routing protocols use link-state, Open Shortest Path First (OSPF) and Intermediate System to Intermediate System (IS-IS). Open Shortest Path First (OSPF) and Intermediate System to Intermediate System (IS-IS) share many similarities and also have many differences. Both routing protocols provide the necessary routing functionality.

Open Shortest Path First (OSPF)

The Open Shortest Path First (OSPF) protocol is the most popular protocol use link-state. The Internet Engineering Task Force (IETF) designed OSPF in 1987. Currently, the OSPF has two working versions.  OSPFv2 for IPv4 networks explained in RFC 2328, is an open standard. The second version is OSPFv3 for IPv6 networks, explained in RFC 2740. The OSPFv3 also support IPv4 addresses. Open Shortest Path First (OSPF) is an open standard and it will run on most types of routers. Open Shortest Path First (OSPF) uses the Dijkstra algorithm, to provide a loop-free topology. Its provide fast convergence with triggered and incremental updates via Link State Advertisements (LSAs). It is also a classless protocol and allows for a hierarchical design with VLSM and route summarization.

Intermediate System to Intermediate System (IS-IS)

Intermediate System to Intermediate System (IS-IS), is an open standard routing protocol designed by International for Standardization (ISO) and described in ISO 10589.  It was originally designed for the Open System Interconnection (OSI) protocol suite and not for the TCP/IP protocol suite. Later, Integrated IS-IS, or Dual IS-IS, start providing support for IP networks. Though IS-IS has known as the routing protocol for Internet Service Providers(ISPs) and carriers; more enterprise networks are beginning to use IS-IS. The ISPs and carriers use IS-IS because of its scalability and strength. It is much easier than OSPF to build a large network. IS-IS carries a payload of reachability data, but for the most part, it doesn’t care what’s in the payload.