NETGEAR M7100, M4100 manual Ospf, Open Shortest Path First

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