How to configure BGP Attribute multi-exit discriminator (MED) on Cisco routers?
BGP multi-exit discriminator (MED) Attribute
The multi-exit discriminator (MED) or metric attribute is used as a suggestion to an external AS regarding the preferred route into the AS that is advertising the metric. The term suggestion is used because the external AS that is receiving the MEDs may be using other BGP attributes for route selection. MEDs are advertised throughout the local AS. Router having smaller value of metric shall be preferred.
RUNNING RIP ON ROUTER-A
A(config)# router rip
A(config-router)# network 200.100.50.0
A(config-router)# network 1.0.0.0
RUNNING EBGP ON ROUTER-A
A(config)# router bgp 10
A(config-router)# no synchronization
A(config-router)# neighbor 1.1.1.2 remote-as 20
A(config-router)# neighbor 4.1.1.1 remote-as 20
A(config-router)# network200.100.50.0
RUNNING EBGP ON ROUTER-B
B(config)# router bgp 20
B(config-router)# no synchronization
B(config-router)# neighbor 1.1.1.1remote-as 10
RUNNING EBGP ON ROUTER-D
D(config)# router bgp 20
D(config-router)# no synchronization
D(config-router)# neighbor 4.1.1.2 remote-as 10
RUNNING OSPF ON ROUTER-B
B(config)# router ospf 1
B(config-router)# network 2.0.0.0 0.255.255.255 area 0
B(config-router)# network 1.0.0.0 0.255.255.255 area 0
RUNNING OSPF ON ROUTER-C
C(config)# router ospf 1
C(config-router)# network 2.0.0.0 0.255.255.255 area 0
C(config-router)# network 3.0.0.0 0.255.255.255 area 0
RUNNING OSPF ON ROUTER-D
D(config)# router ospf 1
D(config-router)# network 3.0.0.0 0.255.255.255 area 0
D(config-router)# network 4.0.0.0 0.255.255.255 area 0
RUNNING IBGP ON ROUTER-B
B(config)# router bgp 20
B(config-router)# no synchronization
B(config-router)# neighbor 4.1.1.1remote-as 20
B(config-router)# neighbor 2.1.1.2remote-as 20
RUNNING IBGP ON ROUTER-C
C(config)# router bgp 20
C(config-router)# no synchronization
C(config-router)# neighbor 2.1.1.1remote-as 20
C(config-router)# neighbor 3.1.1.2remote-as 20
RUNNING IBGP ON ROUTER-D
D(config)# router bgp 20
D(config-router)# no synchronization
D(config-router)# neighbor 3.1.1.1remote-as 20
D(config-router)# neighbor 2.1.1.1remote-as 20
A(config)# access-list 31 permit 200.100.50.00.0.0.255
A(config)# route-map upper permit 11
A(config-route-map)# match ip address 31
A(config-route-map)# set metric 50
A(config-route-map)# exit
A(config)# route-map lower permit 11
A(config-route-map)# match ip address 31
A(config-route-map)# set metric 100
A(config-route-map)# exit
A(config)#
A(config)# router bgp 10
A(config-router)# neighbor 4.1.1.1 route-map upper out
A(config-router)# neighbor 1.1.1.2 route-map lower out
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