How to configure BGP MED Attribute 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
DEFINING 4 STATIC ROUTES ON ROUTER-A
A(config)# ip route 192.1.18.0 255.255.255.0 null 0
A(config)# ip route 192.1.19.0 255.255.255.0 null 0
A(config)# ip route 192.1.20.0 255.255.255.0 null 0
REDISTRIBUTION OF STATIC ROUTES INTO BGP 10 on ROUTER-A
A(config)# router bgp 10
A(config-router)# redistribute static
CREATING ACCESS-LIST ON ROUTER-A
A(config)# access-list 81 permit 200.100.50.0 0.0.0.255
A(config)# access-list 81 permit 192.1.17.0 0.0.0.255
A(config)# access-list 81 permit 192.1.18.0 0.0.0.255
A(config)# access-list 82 permit 192.1.19.0 0.0.0.255
A(config)# access-list 82 permit 192.1.20.0 0.0.0.255
CREATING ROUTE-MAP (AD) ON ROUTER-A
A(config)# route-map AD permit 10
A(config-route-map)# match ip address 81
A(config-route-map)# set metric 50
A(config-route-map)# exit
A(config)# route-map AD permit 20
A(config-route-map)# match ip address 82
A(config-route-map)# set metric 120
CREATING ROUTE-MAP (AB) ON ROUTER-A
A(config)# route-map AB permit 10
A(config-route-map)# match ip address 82
A(config-route-map)# set metric 60
A(config-route-map)# exit
A(config)# route-map AB permit 20
A(config-route-map)# match ip address 81
A(config-route-map)# set metric 100
APPLYING ROUTE-MAP (AD & AB) ON ROUTER-A
A(config)# router bgp 10
A(config-router)# neighbor 4.1.1.1 route-map AD out
A(config-router)# neighbor 1.1.1.2 route-map AB out
A# clear ip bgp *
B# show ip bgp
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