ECS4100 Series Web Management Guide-R07

Chapter 18 | Unicast Routing
Configuring the Routing Information Protocol
– 682 –
◆ RIP Default Metric – Sets the default metric assigned to external routes
imported from other protocols. (Range: 1-15; Default: 1)
The default metric must be used to resolve the problem of redistributing
external routes with incompatible metrics.
It is advisable to use a low metric when redistributing routes from another
protocol into RIP. Using a high metric limits the usefulness of external routes
redistributed into RIP. For example, if a metric of 10 is defined for redistributed
routes, these routes can only be advertised to routers up to 5 hops away, at
which point the metric exceeds the maximum hop count of 15. By defining a
low metric of 1, traffic can follow a imported route the maximum number of
hops allowed within a RIP domain. However, note that using a low metric can
increase the possibility of routing loops. For example, this can occur if there are
multiple redistribution points and the router learns about the same external
network with a better metric from a redistribution point other than that
derived from the original source.
The default metric does not override the metric value set in the Redistribute
screen (see “Configuring Route Redistribution” on page 689). When a metric
value has not been configured in the Redistribute screen, the default metric
sets the metric value to be used for all imported external routes.
◆ RIP Max Prefix – Sets the maximum number of RIP routes which can be
installed in the routing table. (Range: 1-24; Default: 24)
◆ Default Information Originate – Generates a default external route into the
local RIP autonomous system. (Default: Disabled)
A default route is set for every Layer 3 interface where RIP is enabled. The
response packet to external queries marks each active RIP interface as a default
router with the IP address 0.0.0.0.
◆ Default Distance – Defines an administrative distance for external routes
learned from other routing protocols. External routes are routes for which the
best path is learned from a neighbor external to the local RIP autonomous
system. Routes with a distance of 255 are not installed in the routing table.
(Range: 1-255; Default: 120)
Administrative distance is used by the routers to select the preferred path when
there are two or more different routes to the same destination from two
different routing protocols. A smaller administrative distance indicates a more
reliable protocol.
Use the Routing Protocol > RIP > Distance page (see page 691) to configure the
distance to a specific network address, or to configure an access list that filters
networks according to the IP address of the router supplying the routing
information.
◆ Number of Route Changes – The number of route changes made to the IP
route database by RIP.
◆ Number of Queries – The number of responses sent to RIP queries from other
systems.