Switch User Manual

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 per iodically 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

5.1 27 August 2007