Nortel Networks NN47200-503 manual Limitations, Open Shortest Path First Ospf protocol, Overview

	IP routing 27
rip1OrRip2	RIP version 1 or RIP version 2 updates are accepted.
rip1	RIP version 1 and RIP version 1 compatible updates only are
	accepted.
rip2	RIP version 2 updates only are accepted.

Limitations

RIP has the following limitations:

•The protocol is limited to networks whose longest path is 15 hops.

•The protocol depends on counting to infinity to resolve certain unusual situations.

•The protocol uses fixed metrics (the hop number) to compare alternative routes, as opposed to real-time parameters such as measured delay, reliability, or load.

•RIP does not support address-less links.

Open Shortest Path First (OSPF) protocol

The Open Shortest Path First (OSPF) Protocol is an Interior Gateway Protocol (IGP) that distributes routing information between routers belonging to a single autonomous system (AS). Intended for use in large networks, OSPF is a link-state protocol which supports IP subnetting and the tagging of externally-derived routing information.

Note: The Nortel Ethernet Routing Switch 5500 Series implementation of OSPF only supports broadcast and passive interfaces. Point-to-point and NBMA interfaces are not supported.

Overview

In an OSPF network, each router maintains a link-state database that describes the topology of the autonomous system (AS). The database contains the local state for each router in the AS, including the router’s usable interfaces and reachable neighbors.

Each router periodically checks for changes in its local state and shares any changes detected by flooding link-state advertisements (LSAs) throughout the AS. Routers synchronize their topological databases based on the sharing of information from LSAs.

From the topological database, each router constructs a shortest-path tree, with itself as the root. The shortest-path tree gives the optimal route to each destination in the AS. Routing information from outside the AS appears on the tree as leaves.

OSPF routes IP traffic based solely on the destination IP address and subnet mask contained in the IP packet header.

Nortel Ethernet Routing Switch 5500 Series

Configuration-IP Routing Protocols

NN47200-503 03.01 Standard

5.127 August 2007

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