Netgear XSM4324FS Software Administration Manual Software Version 12.x - Page 108

M4300 Series and M4300-96X Fully Managed Switches Open Shortest Path First Concepts 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 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. Inter-area Router The examples in this section show you how to configure the switch first as an inter-area router and then as a border router. They show two areas, each with its own border router connected to one inter-area router. The following figure shows a network segment with an inter-area router connecting areas 0.0.0.2 and 0.0.0.3. The sample script shows the commands used to configure the switch as the inter-area router in the diagram by enabling OSPF on port 1/0/2 in area 0.0.0.2 and port 1/0/3 in area 0.0.0.3. OSPF 108 Software Administration Manual