80OSPF configurationOSPF is a link state interior gateway protocol developed by the OSPF working group of the IETF.At present, OSPF version 2 (RFC 2328) is used.• The term router in this document refers to both routers and Layer 3 switches.• Unless otherwise noted, OSPF refers to OSPFv2 throughout this document.Introduction to OSPFOSPF has the following features:• Wide scope: OSPF supports networks of various sizes and up to several hundred routers inan OSPF routing domain.• Fast convergence: OSPF transmits routing updates instantly upon network topology changes.• Loop free: OSPF computes routes with the SPF algorithm to avoid routing loops.• Area-based network partition: Splits an AS into different areas to facilitate management. Inaddition, routing information transmitted between areas is summarized to reduce traffic androuting table sizes.• ECMP routing: Supports multiple equal-cost routes to a destination.• Routing hierarchy: Supports a four-level routing hierarchy that prioritizes routes into intra-area, inter-area, external Type-1, and external Type-2 routes.• Authentication: Supports interface-based packet authentication to ensure the security ofpacket exchange.• Support for multicast: Multicasts protocol packets on some types of links.Basic conceptsAutonomous systemA set of routers using the same routing protocol to exchange routing information constitute an AS.OSPF route computationOSPF route computation is described as follows:• Based on the network topology around itself, each router generates LSA and sends them toother routers in update packets.
