Black Box LGB6026A, Management Manual

Page: 522 / 1289

C
HAPTER
21 | Unicast Routing
Configuring the Routing Information Protocol
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RIP send/receive versions set on the RIP Interface settings screen
(
page 530 ) always take precedence over the settings for the Global RIP
Version. However, when the Global RIP Version is set to “By Interface,”
any VLAN interface not previously set to a specific receive or send
version is set to the following default values:
■
Receive: Accepts RIPv1 or RIPv2 packets.
■
Send: Route information is broadcast to other routers with RIPv2.
◆
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 527 ). 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: 1-7168; Default: 7168)
◆
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 529 ) to
configure the distance to a specific network address, or to configure an