Netgear M4100-26G Software Administration Manual - Page 86

7. OSPF 7 Open Shortest Path First This chapter provides the following examples: • Inter-area Router on page 87 • OSPF on a Border Router on page 92 • Stub Areas on page 98 • nssa Areas on page 107 • VLAN Routing OSPF on page 116 • OSPFv3 on page 122 For larger networks Open Shortest Path First (OSPF) is generally used in preference to RIP. OSPF offers several benefits to the administrator of a large or complex network: • Less network traffic: - Routing table updates are sent only when a change has occurred. - Only the part of the table which has changed is sent. - Updates are sent to a multicast, not a broadcast, address. • Hierarchical management, allowing the network to be subdivided. The top level of the hierarchy of an OSPF network is known as an autonomous system (AS) or routing domain, and is a collection of networks with a common administration and routing strategy. The AS is divided into areas: Intra-area routing is used when a source and destination address are in the same area, and inter-area routing across an OSPF backbone is used when they are not. An inter-area router communicates with border routers in each of the areas to which it provides connectivity. The M4100 and M7100 Managed Switch operating as a router and running OSPF determines the best route using the assigned cost and the type of the OSPF route. The order for choosing a route if more than one type of route exists is as follows: • Intra-area. • Inter-area. • External type 1: The route is external to the AS. • External type 2: The route was learned from other protocols such as RIP. Chapter 7. OSPF | 86