47. MED routing for BGP configuration experiment
1. As-path routing analysis
Attribute
Spread range
Default value
Priority value direction
Note: weight this router this router is 32768, other routers 0 large value priority INCISCO private
Local preferenceAS Internal 100th: border router, advertised to IBGP neighbors, telling how to leave this AS large value priority OUT
No short priority IN and OUT between As pathAS
Internal 0 of MEDAS: notify EBGP to tell you how to enter this AS small priority OUT
How to modify the MED value:
2. Experimental topology
3. Basic configuration
R1 configuration
Interface Loopback0
Ip address 1.1.1.1 255.255.255.0
Interface Serial0/0
Ip address 13.1.1.1 255.255.255.0
Interface Serial0/1
Ip address 14.1.1.1 255.255.255.0
Router ospf 110
Router-id 1.1.1.1
Log-adjacency-changes
Network 1.1.1.0 0.0.0.255 area 0
Network 14.1.1.0 0.0.0.255 area 0
Router bgp 4
No synchronization
Bgp router-id 1.1.1.1
Neighbor 4.4.4.4 remote-as 4
Neighbor 4.4.4.4 update-source Loopback0
Neighbor 4.4.4.4 next-hop-self
Neighbor 13.1.1.3 remote-as 3
No auto-summary
R2 configuration
Interface Loopback0
Ip address 2.2.2.2 255.255.255.0
Interface Serial0/1
Ip address 23.1.1.2 255.255.255.0
Interface FastEthernet1/0
Ip address 24.1.1.2 255.255.255.0
Router ospf 110
Router-id 2.2.2.2
Network 2.2.2.0 0.0.0.255 area 0
Network 24.1.1.0 0.0.0.255 area 0
Router bgp 4
No synchronization
Bgp router-id 2.2.2.2
Neighbor 4.4.4.4 remote-as 4
Neighbor 4.4.4.4 update-source Loopback0
Neighbor 4.4.4.4 next-hop-self
Neighbor 23.1.1.3 remote-as 3
No auto-summary
R3 configuration
Interface Loopback0
Ip address 3.3.3.3 255.255.255.0
Interface Loopback1
Ip address 33.33.33.33 255.255.255.0
Interface Serial0/0
Ip address 13.1.1.3 255.255.255.0
Interface Serial0/1
Ip address 23.1.1.3 255.255.255.0router bgp 3
No synchronization
Bgp router-id 3.3.3.3
Network 3.3.3.0 mask 255.255.255.0
Network 33.33.33.0 mask 255.255.255.0
Neighbor 13.1.1.1 remote-as 4
Neighbor 23.1.1.2 remote-as 4
No auto-summary
R4 configuration
Interface Loopback0
Ip address 4.4.4.4 255.255.255.0
Interface Serial0/1
Ip address 14.1.1.4 255.255.255.0
Interface FastEthernet1/0
Ip address 24.1.1.4 255.255.255.0
Router ospf 110
Router-id 4.4.4.4
Network 4.4.4.0 0.0.0.255 area 0
Network 14.1.1.0 0.0.0.255 area 0
Network 24.1.1.0 0.0.0.255 area 0
Router bgp 4
No synchronization
Bgp router-id 4.4.4.4
Network 4.4.4.0 mask 255.255.255.0
Neighbor 1.1.1.1 remote-as 4
Neighbor 1.1.1.1 update-source Loopback0
Neighbor 2.2.2.2 remote-as 4
Neighbor 2.2.2.2 update-source Loopback0
No auto-summary
4. Default routing
According to Article 10 of the BGP routing principle, R3 reaches 4.4.4.0 and 24 goes through R1 by default.
5. Modify the MED value to allow R3 to access 4.4.4.0Universe 24 from R2.
R1 configuration
Ip prefix-list 1 seq 5 permit 4.4.4.0/24
Route-map MED permit 10
Match ip address prefix-list 1
Set metric 10
Route-map MED permit 20
Router bgp 4
Neighbor 13.1.1.3 route-map MED out
