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| 8.3 |  | Route Redistribution |
| 8.3.5 |  | Configuring one-way redistribution |

Although the redistribution command is available for all IP routing protocols, it behaves differently depending on the actual IP routing protocols involved. However, the underlying principles are the same. Therefore, the examples in this section can be used as a starting point for any redistribution scheme.

This section closely examines examples of one-way and two-way redistribution and then focuses on specific redistribution issues, including connected, static routes and the default-metric command.

In Figure , RTB injects routes learned by way of RIP into the EIGRP domain. However, the RIP routers do not learn about the EIGRP routes. This is one-way route distribution. In this example, the RIP routers can use a default route to handle any traffic bound for nonlocal destinations.

As the AS boundary router, RTB must run two routing processes, one for the RIP domain and one for the EIGRP AS.

The syntax of the redistribute command is as follows:

> Router(config-router)#redistribute protocol [process-id] {level-1 | level-1-2 | level-2} [metric metric-value][metric-type type-value] [match {internal | external 1 | external 2}][tag tag-value] [route-map map-tag][weight weight] [subnets]

The redistribute rip command enables route redistribution. RIP routes learned by RTB will be imported into the EIGRP process. The metric argument sets up the values used by EIGRP to translate the metric from the hop count on RIP to the composite metric on EIGRP. When used with IGRP/EIGRP, the metric keyword sets the bandwidth value, the delay, the reliability, the load, and the maximum transmission unit (MTU). The bandwidth value is in Kbps, the delay is in tenths of microseconds, while the reliability and the load are out of 255.

These five values constitute the seed metric. The seed metric is the initial metric value of an imported route. After it is imported into the EIGRP AS, the RIP route becomes an EIGRP route with a composite metric derived from these seed values. Using the configuration in Figure , RIP routes with metrics of two (2), six (6), and 14 will be redistributed with the same EIGRP metric value of 2195456. However, as the imported route propagates to other EIGRP routers, its metric values increment according to EIGRP rules.

Click on the topology in Figure to examine the routing tables of the EIGRP router, RTA, for the boundary router, RTB, and for the RIP router, RTC. The tables have been reformatted for the purpose of clarity.

The routing table on RTA includes not only the EIGRP routes from AS 24, but also the redistributed routes from the RIP domain. The redistributed RIP routes that have been learned from RTB are denoted by D EX because EIGRP considers them external. As discussed in Module 5, EIGRP differentiates between internal routes, routes, and external routes. Internal routes are learned from within the AS, while external routers are imported from outside the AS. The Cisco IOS assigns a different administrative distance of 170 to the external EIGRP routes, which is much less desirable.

The table from RTB shows that RTB is running two routing protocols and has learned routes by way of RIP and learned routes by way of EIGRP. RIP is denoted by an R and EIGRP is denoted by a D.

Notice that RTC does not have a default route and has not learned about any routes from the boundary router, RTB. That means that RTC cannot route to six (6) of the 12 networks shown in the outputs of Figure . It may be decided that the best solution in this scenario is to use a default route that points to RTB. This can easily be accomplished statically, as the following shows:

> RTC(config)#ip route 0.0.0.0 0.0.0.0 172.16.0.1

Because RTC is running RIP, it can dynamically propagate its 0.0.0.0/0 route to the other routers in the RIP domain. If choosing to implement this default route configuration, there is no need for the boundary router, RTB, to send updates into the RIP domain. Therefore the RIP interface on RTB should be configured as passive, as the following shows:

> RTB(config)#router rip
> RTB(config-router)#passive-interface s0

A more complex topology may require that a two-way, or mutual, redistribution be employed. This is done by importing the EIGRP routes into the RIP domain, as described in the next section.

| Lab Activity e-Lab Activity: Configuring One-way Redistribution This lab is to configure RTB router to accomplish a one-way redistribution of RIP domain.