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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
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:
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.
Click on the topology in Figure
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
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:
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.
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