User Guide

Local Management
1-42 Local Management User’s Guide
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 IPv6-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 IPv6 prefix of the destination
• A metric, described above
• The IPv6 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.
Authentication — Authentication is a function of RIP-2 protocol only. It is not usually important
to conceal the information in the routing messages, but it is essential to prevent the insertion of
bogus routing information into the routers. Authentication prevents someone who cannot directly
access the network (i.e., someone who cannot sniff the packets to determine the password) from
inserting bogus routing information. Currently the authentication type is simple password and
MD5.
Multicasting — The RIP-2 protocol provides for the IP multicasting of periodic advertisements.
This feature was added to RIP-2 to decrease the load on systems that do not support RIP-2. It also
provides a mechanism whereby RIP-1 routers will never receive RIP-2 routes. This feature is
useful when the correct use of an advertised route depends on knowing the precise subnet mask,
which would be ignored by a RIP-1 router.