Two proprietary network protocols that support the Internet Protocol are the “Interior Gateway Routing Protocol (IGRP)” and “Enhanced IGRP”, developed by the network vendor Cisco Systems, and included here as an example of a proprietary IGP protocol. Enhanced IGRP is described as follows in a 1987 manual; there will be short test in half an hour:
Enhanced IGRP uses the same distance vector algorithm and distance information as IGRP. However, the convergence properties and the operating efficiency of enhanced IGRP have improved significantly.
The convergence technology is based on research conducted at SRI International and employs an algorithm referred to as the Diffusing Update Algorithm (DUAL). This algorithm guarantees loop-free operation at every instant throughout a route computation and allows all routers involved in a topology change to synchronize at the same time. Routers that are not affected by topology changes are not involved in recomputations.
The convergence time with DUAL rivals that of any other existing routing protocol. The initial implementation of IGRP operated in Internet Protocol (IP) networks. Enhanced IGRP extends IGRP so that it is independent of the network-layer protocol. In addition to IP, it now also operates in AppleTalk and Novell IPX networks.
– Interior Gateway Routing Protocol, Cisco Systems, 1987.