45. Local preference routing for BGP configuration experiment
1. Local preference 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
How to modify the Local preference value:
Method 1: modify all the Local preference values of routes advertised to IBGP neighbors, for example:
Router bgp 4
Bgp default local-preference 125
Method 2: partially modify the Local preference value of routes advertised to IBGP neighbors, for example:
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
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 the eighth rule of BGP routing principle, R4 reaches 3.3.3.0 pick 24 and 33.33.33 pick 24 all pass through R2.
5. Modify the Local preference values of all routes advertised to IBGP neighbors
From the front can R4 to 3.3.3.0ax 24, 33.33.330C24 all go through R2, we change the Local cover value to make R4 reach 3.3.3.0Universe 24, 33.33.0Universe 24 all pass through R1.
R4 configuration
Router bgp 4
Bgp default local-preference 125
6. Partially modify the Local preference value of routes advertised to IBGP neighbors
R4 to 3.3.3.0Compact 24 and 33.33.330Universe 24 are all through R2. We change the Local promise value to make R4 reach 3.3.3.0Compact 24 through R2 and 33.33.33.0 Universe 24 through R1.
R4 configuration
Ip prefix-list 1 seq 5 permit 33.33.33.0/24
No cdp log mismatch duplex
Route-map L permit 10
Match ip address prefix-list 1
Set local-preference 125
Route-map L permit 20
Router bgp 4
Neighbor 4.4.4.4 route-map L out
