Route redistribution allows routes learned by one routing protocol to be advertised to another protocol. This is necessary when different protocols are used in the same internetwork due to vendor or other requirements. The redistribution device runs both protocols and shares routes between them, but external redistributed routes have lower preference than internally learned routes. Metrics must be translated between protocols since they use different metrics like hop count, bandwidth, and cost.

1. Route Redistribution
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2.  Route redistribution is a technique that allows
routes learned by one routing protocol or
algorithm to be advertised into another routing
protocol or algorithm.
 For the simplicity and ease of management of an
internetwork, it is always preferred to use a
single routing protocol or algorithm. However,
this is not always possible, because each
internetwork has its own requirements,
limitations, and conditions.
 For example, consider an internetwork that
consists of 100 of routers of different vendors
such as Cisco and Juniper. You cannot use the
EIGRP routing protocol because it is a Cisco-
proprietary protocol (but now a days It become
open standard) and does not support routers of
other vendors such as Juniper. So, the multi-
protocol implementation is common in the multi-
vendor environments.

3.  Routes learned by the Route Redistribution
technique are marked as external routes (EIGRP
& OSPF) in the routing table. The external routes
have less preference over the locally-learned
routes.
 In order to redistribute routes from one routing
protocol to another routing protocol, there must
be at least one redistribution point (device).
 The redistribution device will run both routing
protocols.
 For example, if you want to redistribute the
routes learned by the RIP routing protocol into
the EIGRP routing protocol, at least one interface
of the redistribution device should be included in
the RIP routing domain and at least one another
interface should be included in the EIGRP routing
domain.

4. Note: - Keep in mind, routes that are stored in a topology database
(topology table) are not redistributed.

5.  One of the most important factors that needs
to be considered while performing route
redistribution is Metric.
 Each routing protocol uses a unique metric to
calculate the best path to a destination
network.
 For example,
◦ RIP protocol uses the hop count metric
◦ EIGRP protocol uses the composite (bandwidth,
load, delay, and reliability) metric.
◦ OSPF protocol uses the cost
 The metric value of an injecting protocol (the
protocol of which you want to redistribute
routes) should be defined in such a manner
that it can be understood by the receiving
protocol (the protocol to which you want to
redistribute routes).