Configuring Rip; Overview; Rip Route Entries; Rip Timers - HP MSR Series Configuration Manual

Configuring RIP

Routing Information Protocol (RIP) is a distance-vector simple interior gateway protocol suited to
small-sized networks. It employs UDP to exchange route information through port 520.

Overview

RIP uses a hop count to measure the distance to a destination. The hop count from a router to a directly
connected network is 0. The hop count from a router to a directly connected router is 1. To limit
convergence time, RIP restricts the metric range from 0 to 15. A destination of a metric value of 16 (or
greater) is considered unreachable. For this reason, RIP is not suitable for large-sized networks.

RIP route entries

RIP stores routing entries in a database. Each routing entry contains the following elements:
Destination address—IP address of a destination host or a network.
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Next hop—IP address of the next hop.
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Egress interface—Egress interface of the route.
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Metric—Cost from the local router to the destination.
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• Route time—Time elapsed since the last update. The time is reset to 0 every time the routing entry
is updated.
Route tag—Used for control routes. For more information, see "Configuring routing policies."
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RIP timers

RIP uses the following timers:
Update timer—Specifies the interval between route updates.
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• Timeout timer—Specifies the route aging time. If no update for a route is received within the aging
time, the metric of the route is set to 16.
Suppress timer—Specifies the duration a RIP route stays in suppressed state. When the metric of a
•
route is 16, the route enters the suppressed state. A suppressed route can be replaced by an update
route that is received from the same neighbor before the suppress timer expires and has a metric
less than 16.
Garbage-collect timer—Specifies the interval from when the metric of a route becomes 16 to when
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it is deleted from the routing table. RIP advertises the route with a metric of 16. If no update is
announced for that route before the garbage-collect timer expires, the route is deleted from the
routing table.

Routing loop prevention

RIP uses the following mechanisms to prevent routing loops:
• Counting to infinity—A destination with a metric value of 16 is considered unreachable. When a
routing loop occurs, the metric value of a route will increment to 16 to avoid endless loopings.
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