Next Hop; Metrics; Split Horizon - Cabletron Systems CyberSWITCH CSX200 Configuration Manual

Configuration with QuickSET

Next Hop

Entries in RIP-2 routing tables always have a Next Hop field. The Next Hop is the IP address of the
next router along the path to the destination. The purpose of the Next Hop in the routing table is to
prevent packets from being routed through extra hops in the system. The limitation of a maximum
network diameter of 15 hops for the Next Hop field is common to both RIP-1 and RIP-2. This
statement of the limit assumes that a cost of 1 is used for each network (see Metrics, below). The
Next Hop field will contain a number between 1 and 15 inclusive. A number of 16 means that the
network is unreachable.

Metrics

The RIP-1 and RIP-2 protocols use fixed "metrics" to compare alternative routes. This is not
appropriate where routes need to be chosen based on real-time parameters such as measured delay,
reliability, or load. RIP is intended to allow routers to exchange information for computing routes
through an IP-based network. Any router that uses RIP is assumed to have interfaces to one or
more networks, otherwise it isn't a router. These are referred to as directly connected networks.
The RIP protocol relies on access to certain information about each of these networks, the most
important of which is its metric. This metric represents the total "cost" of getting a datagram from
the router to that destination.
The routing table has the entries listed below for each destination that is reachable:
• The IP prefix of the destination
• A metric, described above
• The IP address of the next router along the path (the Next Hop)
• A flag to indicate the information about the route has changed recently
• Various timers associated with the route

Split Horizon

Split Horizon is an algorithm for avoiding problems caused by including routes in the updates sent
to the gateway from which they were learned. The basic split horizon algorithm omits routes
learned from one neighbor in updates sent to that neighbor.
128 QuickSET Configuration Guide