Redistribution

A lot of students are confused by redistribution. Actually in a nutshell, it is just borrowing routes from other protocols and advertising them as your own routes. Why borrowing? Sometimes you are merging the networks of two different organizations (one running on EIGRP and another running on OSPF). Generally people are resistant to changes and do not want to change their networks to cater for the other party. Thus, redistribution is useful in this scenario here. You only need to make changes on the network boundaries or border router (converting EIGRP to OSPF routes and vice versa). This way, it enables networks running on different routing protocols to work with one another in a seamless manner.

For the border router, you need to run the following commands (assuming a border router with 3 different routing protocols and static routes configured)

router eigrp xx
redistribute rip metric 10000 100 255 1 1500
redistribute ospf xx metric 10000 100 255 1 1500
redistribute static metric 10000 100 255 1 1500

router rip
redistribute ospf xx metric 1
redistribute eigrp xx metric 1
redistribute static metric 1

router ospf xx
redistribute eigrp xx metric 1 subnets
redistribute rip metric 1 subnets
redistribute static metric 1 subnets

The values used are default values. It will be useful to rememeber them.