9.6 BGP Redistribution
9.6.4 BGP redistribution configuration example
As with IGP routes, all known static routes can be injected into BGP using the redistribute command, or a subset of static routes can be injected using the BGP network command. Again, the network command provides greater control, while increasing the administrative burden.

The figure demonstrates how routing information can be injected dynamically into BGP.
You can configure RTB in the figure to redistribute OSPF-learned routes into BGP dynamically:

RTB(config)#router bgp 200
RTB(config-router)#neighbor 10.1.1.2 remote-as 100
RTB(config-router)#neighbor 10.1.1.2 route-map BLOCK-BAD-ADDRESSES out
RTB(config-router)#redistribute ospf 1 match internal metric 50
RTB(config-router)#redistribute static

For insurance, you can configure a route map that matches any private addresses that you do not want advertised outside the AS. The route map, appropriately called BLOCK-BAD-ADDRESSES, is applied to outbound BGP updates. Also, BGP has been configured to redistribute only internal OSPF routes and assign them a metric of 50. The redistribute static command will dynamically populate BGP with any static routes that RTB happens to be configured with.

Alternatively, you can configure RTB to inject internal routes semidynamically, by using the BGP network command:

RTB(config)#router bgp 200
RTB(config-router)#neighbor 10.1.1.2 remote-as 100
RTB(config-router)#neighbor 10.1.1.2 route-map BLOCK-BAD-ADDRESSES out
RTB(config-router)#network 192.168.1.0
RTB(config-router)#network 192.168.2.0

If you configure RTB accordingly, it will not inject all the internal routes into BGP. Only the two networks specified, 192.168.1.0 and 192.168.2.0, will be injected (although you could have configured them all the same way). In a sense, the BGP network command redistributes the specified IGP route into BGP, allowing for precise control.