Switch User Manual

IP routing 23

Non-local static routes

The Nortel Ethernet Routing Switch 5500 Series supports the usage of

non-local static routes. A non-local static route is almost identical to a

static route with the exception that the next hop of the route is not directly

connected to the network entity. Non-local static routes are useful in

situations where there are multiple paths to a network and the number

of static routes could be reduced by using only one route with a remote

gateway.

Because of their static nature, this type of solution is not scalable. Thus,

in a large or growing network this type of route management may not

be desirable. Also, non-local static routes do not have the capacity to

determine the failure of paths. Thus, a router can still attempt to use a path

after it has failed.

Routing Information Protocol (RIP)

Routing Information Protocol (RIP) is a standard, dynamic routing protocol

based on the Bellman-Ford (or distance vector) algorithm. It is used as an

Interior Gateway Protocol (IGP). RIP allows routers to exchange information

to compute routes through an IPv4-based network. The hop count, or

distance, is used as a metric to determine the best path to a remote network

or host. The hop count cannot exceed 15 hops (assuming a cost of one

hop for each network).

RIP is deﬁned in RFC 1058 for RIP version 1 and RFC 2453 for RIP version

2. The most signiﬁcant difference between the two versions is that RIP

version 2 supports subnet masks and next hop information in the RIP

packet.

RIP operation

RIP uses User Datagram Protocol (UDP) data packets to exchange

routing information. Each router maintains a routing table, which lists the

optimal route to every destination in the system. Each router advertises

its routing information by sending a routing infor mation update at regular

intervals. Neighboring routers use this information to recalculate their

routing tables and retransmit the routing information. For RIP version 1,

no mask information is exchanged; the natural mask is always applied by

the router receiving the update. For RIP version 2, mask infor mation is

always included.

The sequence of processes governed by the routing algor ithm is as follows:

1. When a router starts, it initializes the RIP data structures and then waits

for indications from lower-level protocols that its interfaces are functional.

2. RIP advertisements are send on all the interfaces that are conﬁgured to

send routing information.

Nortel Ethernet Routing Switch 5500 Series

Conﬁguration-IP Routing Protocols

NN47200-503 03.01 Standard

5.1 27 August 2007