Redistributing Dynamic Routes

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Syntax:

router(config-router)# redistribute protocol metric metric

router(config-router)# redistribute protocol metric metric

© 2002. Cisco Systems. Inc- All rights reserved-

Routes learned from routing protocol redistribution are marked as incomplete

© 2002. Cisco Systems. Inc- All rights reserved-

Cisco CCIE Prep v1-0—Module 8-61

redistribute protocol metric metric

Another way to advertise networks is to redistribute dynamic routes. Typically, you redistribute Interior Gateway Protocol (IGP) routes (such as Enhanced Interior Gateway Routing Protocol (EIGRP), IGRP, Intermediate System to Intermediate System (IS-IS), Open Shortest Route First (OSPF), and Routing Information Protocol (RIP) routes) into BGP. Some of your IGP routes might have been learned from BGP, so you need to use access lists to prevent the redistribution of routes back into BGP.

Routers R2 and R3 are running iBGP. R3 is learning 4.4.4.0/24 via BGP, and redistributing 4.4.4.0/24 back into Enhanced IGRP. The following commands configure R3:

R3(config)# router eigrp 10 R3(config-router)# network 3.3.3.0 R3(config-router)# redistribute bgp 230 R3(config-router)# redistributed connected R3(config-router)# default-metric 1000 100 250 1 1500 R3(config-router)# exit R3(config)# router bgp 230

R3(config-router)# neighbor 172.16.134.1 remote-as 100 R3(config-router)# neighbor 172.16.23.2 remote-as 230 R3(config-router)# neighbor 172.16.134.1 distribute-list 1 out R3(config-router)# redistribute eigrp 10

R3(config-router)# exit

R3(config)# access-list 1 permit 2.2.2.0 0.0.0.255

The redistribute router configuration command with the eigrp keyword redistributes Enhanced IGRP routes for process ID 10 into BGP.

Note Normally, distributing BGP into IGP should be avoided because too many routes would be injected into the AS.

The neighbor distribute-list router configuration command applies access list 1 to outgoing advertisements to the neighbor whose Internet Protocol (IP) address is 172.16.134.1 (that is, R1). Access list 1 specifies that network 2.2.2.0 is to be advertised. All other networks, such as network 4.4.4.0, are implicitly prevented from being advertised. The access list prevents network 4.4.4.0 from being injected back into BGP as if it originated from AS 230, and allows BGP to advertise network 2.2.2.0 as originating from AS 230.

Redistribution of dynamic routes requires careful use of access lists to prevent updates from being injected back into BGP. If possible, you should use the network command or redistribute static routes instead of redistributing dynamic routes.

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