Route Redistribution
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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.
Route Redistribution
- 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).