Overview
Open Shortest Path First (OSPF) is a link-state IGP developed by the OSPF working group of the IETF. OSPF version 2 is used for IPv4. OSPF refers to OSPFv2 throughout this chapter.
OSPF has the following features:
Wide scope—Supports multiple network sizes and several hundred routers in an OSPF routing domain.
Fast convergence—Advertises routing updates instantly upon network topology changes.
Loop free—Computes routes with the SPF algorithm to avoid routing loops.
Area-based network partition—Splits an AS into multiple areas to facilitate management. This feature reduces the LSDB size on routers to save memory and CPU resources, and reduces route updates transmitted between areas to save bandwidth.
ECMP routing—Supports multiple equal-cost routes to a destination.
Routing hierarchy—Supports a 4-level routing hierarchy that prioritizes routes into intra-area, inter-area, external Type-1, and external Type-2 routes.
Authentication—Supports area- and interface-based packet authentication to ensure secure packet exchange.
Support for multicasting—Multicasts protocol packets on some types of links to avoid impacting other devices.