BGP Route map and MED – GNS3 Lab

In this lab we will learn how to use Route map to set MED attribute to tell which path the neighbor should choose to a specific network.

Topology:

IOS used in this lab: c3640-jk9s-mz.124-16.bin

Tasks in this lab:

1) Set up basic IBGP & EBGP
2) Advertise loopback 1 & loopback 10 on R1
3) Use route-maps on R2 & R3 to set MED for only 192.168.1.0, verify on R6 and will R6 see network 192.168.10.0?

Basic Configuration – IP Assignments

1) Set up IBGP & EBGP connections

Note: The use of a loopback interface to define neighbors is common with iBGP, but is not common with eBGP. Normally, you use the loopback interface to make sure that the IP address of the neighbor stays up and is independent of hardware that functions properly. In the case of eBGP, peer routers frequently have direct connection, and loopback does not apply.

2) Advertise networks 192.168.1.0 & 192.168.10.0 on R1:

On R1 we advertise two networks 192.168.1.0/24 & 192.168.10.0/24:

Now check on both R2 & R3 to see both networks are advertised

Also on EBGP neighbors, these networks are also advertised (you have to wait a moment for BGP updates)

On R6 networks 192.168.1.0 & 192.168.10.0 are learned via both R4 & R5:

Note: the path via R4 (46.46.46.4) are chosen for both networks as the best path because of lower router-ID on R4)

3) Use route-maps on R2 & R3 to set MED for 192.168.1.0 to 150 & 170, respectively:

Now R6 only receives updates about 192.168.1.0. The metric advertised by R3 is lower so it is chosen as the best path to 192.168.1.0 (marked with “>”).

Notice that updates for 192.168.10.0 have been filtered out because there is an implicit “deny all” statement at the end of each access-list.