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Manipulating Redistribution Using Route Tagging

Two-way multipoint redistribution can introduce routing loops in the network. One option to prevent redistribution of already redistributed routes is to use route tagging. In two-way multipoint redistribution scenarios, route tags must be applied and filtered in both direction and on both routers performing redistribution.

Figure 4-9 shows the network topology for the configuration that follows, which demonstrates how to control redistribution with route tags using the commands covered in this chapter. Assume that all basic configurations and EIGRP and OSPF routing have been configured correctly. A tag number of 11 is used to identify OSPF routes, and a tag of 22 is used to identify EIGRP routes.

Figure 4-9

Figure 4-9 Network Topology for Redistribution Using Route Tagging

The following configuration needs to be entered on both the HULL and WENDOVER routers.

HULL(config)#route-map EIGRPtoOSPF deny 10

HULL(config-route-map)#match tag 11

Creates a route map named EIGRPtoOSPF and denies redistribution for all routes tagged with the value 11.

HULL(config-route-map)#route-map EIGRPtoOSPF permit 20

HULL(config-route-map)#set tag 22

Creates a second statement for route map EIGRPtoOSPF permitting all other routes to be redistributed with a tag of 22.

HULL(config-route-map)#route-map OSPFtoEIGRP deny 10

HULL(config-route-map)#match tag 22

Creates a route map names OSPFtoEIGRP and denies redistribution for all routes tagged with the value 22.

HULL(config-route-map)#route-map OSPFtoEIGRP permit 20

HULL(config-route-map)#set tag 11

Creates a second statement for route map OSPFtoEIGRP permitting all other routes to be redistributed with a tag of 11.

HULL(config-route-map)#router ospf 11

Enters OSPF configuration mode.

HULL(config-router)#redistribute eigrp 22 subnets route-map EIGRPtoOSPF

Redistributes all EIGRP routes with a tag of 22 into the OSPF domain.

HULL(config-router)#router eigrp 22

Enters EIGRP configuration mode.

HULL(config-router)#redistribute ospf 11 metric 1500 1 255 1 1500 route-map OSPFtoEIGRP

Redistributes all OSPF routes with a tag of 11 into the EIGRP domain.

NOTE: The result here is to ensure only routes originating in the OSPF domain are redistributed into EIGRP, while only routes originating in the EIGRP domain are redistributed into the OSPF domain.

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