Configuring MED: Single Adjacent AS
Example 13-10 shows an example MED configuration that matches Figure 13-11, with R5 and R7 setting the MED for 11.0.0.0/8 to 10 and 20, respectively.
Example 13-10 Classical MED Example Between Two Ass
It is important that both R5 and R7 set the MED for 11.0.0.0/8. If R5 had set MED to 10, and R7 had done nothing, the router through R7 would have been the best route. R1 and R3 would have used their assumed default setting of 0 for MED for the route through R1 and R7, and, as with IGP metrics, smaller is better with MED. A better default for MED can be set by using the bgp bestpath med missing-as-worst BGP subcommand, which resets a router’s default MED to the largest possible MED value, instead of the lowest. Note that it is important that all routers in the same AS either use the default of 0 or configure this command; otherwise, routing choices will be affected.
Example 13-10 Classical MED Example Between Two Ass
It is important that both R5 and R7 set the MED for 11.0.0.0/8. If R5 had set MED to 10, and R7 had done nothing, the router through R7 would have been the best route. R1 and R3 would have used their assumed default setting of 0 for MED for the route through R1 and R7, and, as with IGP metrics, smaller is better with MED. A better default for MED can be set by using the bgp bestpath med missing-as-worst BGP subcommand, which resets a router’s default MED to the largest possible MED value, instead of the lowest. Note that it is important that all routers in the same AS either use the default of 0 or configure this command; otherwise, routing choices will be affected.
