The TCP/IP Guide  9  TCP/IP Lower-Layer (Interface, Internet and Transport) Protocols (OSI Layers 2, 3 and 4)       9  TCP/IP Internet Layer (OSI Network Layer) Protocols            9  TCP/IP Routing Protocols (Gateway Protocols)                 9  TCP/IP Interior Routing Protocols (RIP, OSPF, GGP, HELLO, IGRP, EIGRP)

OSPF Message Formats 1 TCP/IP Gateway-to-Gateway Protocol (GGP)

The Routing Information Protocol (RIP) and Open Shortest Path First (OSPF) are the two most well-known interior routing protocols used in the TCP/IP suite, and for this reason I have described each in considerable detail. In addition to these, there are several other TCP/IP interior routing protocols that fall into one of two categories. Some are either protocols that are no longer used today but are interesting from a historical perspective, and others are proprietary alternates to RIP and OSPF that you may encounter today in the networking world but perhaps not as often.

In this section, I provide a brief description of four additional TCP/IP interior routing protocols. I begin with a look at two obsolete protocols that played an important role in the early Internet: the Gateway-to-Gateway Protocol (GGP) and the HELLO Protocol. I then describe two interior routing protocols developed by Cisco Systems, which are sometimes seen in the industry today as alternatives to RIP and OSPF: the Interior Gateway Routing Protocol (IGRP) and the Enhanced Interior Gateway Routing Protocol (EIGRP).

OSPF Message Formats 1 TCP/IP Gateway-to-Gateway Protocol (GGP)