47. The Med route of BGP configuration experiment

1. As-path Route Selection Analysis

Property	Propagation Range	Default value	Priority value	Direction	Note
Weight	This router	This router 32768, other routers 0	Big Value First	Inch	Cisco private
Local Preference	As internal	100: Border router, advertise to IBGP neighbor, tell how to leave this as	Big Value First	Out
As Path	As between	No	Short priority	In, out
MED	As internal	0: Circular to EBGP, informing how to enter this as	Small priority	Out

Methods to modify the Med value:

2. Experimental topology

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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 route selection

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5, modify the Med value to let R3 visit 4.4.4.0/24 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

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This article is from the "Open Source Hall" blog, please be sure to keep this source http://kaiyuandiantang.blog.51cto.com/10699754/1722088

47. The Med route of BGP configuration experiment