COMPUTER TIPS

How to configure BGP with weight attribute?

 

 

BGP stands for Border Gateway Protocol is true built-in policy based routing protocols. BGP uses different attribute to implement these polices in route selection process between different autonomous systems. There are some main attributes that BGP uses in route selection process. 

• Weight

• Local preference

• Multi-exit Discriminator or MED

• Origin

• AS_Path

• Next Hop

• Community

We will configure here only weight attribute in detail and the remaining attributes will be discussed in the next tips.

The weight attribute basically a Cisco proprietary technology and considered as first attribute in BGP. The default value of weight is 0 and the range is from 0 to 65535. If we change the weight value of one router that change will not propagate to other router and the route with maximum weight value will be considered as the best route.

Today tip will help you configure BGP between two different autonomous systems. In this case, we will try to configure four different routers with routing protocols RIP and then complete the all routing tables using BGP. At the end, we will change the weight of one route in order to give it preference over a lower one

Follow the network topology of four different class networks in the given figure:

Configuration BGP on Router A

In global configuration Mode: 

A(config)# router bgp 10

A (config-router) # neighbor 40.1.1.2 remote-as 20

A (config-router) # neighbor 70.1.1.1 remote-as 20

A (config-router) # network 210.100.30.0

A (config-router) #end

Configuration to Enable BGP & RIP on Router B

In global configuration Mode: 

B(config)# router bgp 20

B (config-router) # neighbor 40.1.1.1 remote-as 10

B (config-router) # neighbor 50.1.1.2 remote-as 20

B (config-router) # neighbor 60.1.1.2 remote-as 20

B (config-router) #no synchronization

B (config-router) #end

B (config) #router rip

B (config-router) # network 40.0.0.0

B (config-router) # network 50.0.0.0

B (config-router) #end

Configuration to Enable BGP & RIP on Router C

In global configuration Mode: 

C(config)# router bgp 20

C (config-router) # neighbor 50.1.1.1 remote-as 20

C (config-router) # neighbor 60.1.1.2 remote-as 20

C (config-router) #no synchronization

C (config-router) #end

C (config) #router rip

C (config-router) # network 50.0.0.0

C (config-router) # network 60.0.0.0

C (config-router) #end

Configuration to Enable BGP & RIP on Router D

In global configuration Mode: 

D(config)# router bgp 20

D (config-router) # neighbor 70.1.1.2 remote-as 10

D (config-router) # neighbor 50.1.1.1 remote-as 20

D (config-router) # neighbor 60.1.1.1 remote-as 20

D (config-router) #no synchronization

D (config-router) #end

D (config) #router rip

D (config-router) # network 70.0.0.0

D (config-router) # network 60.0.0.0

D (config-router) #end  

Now run show command to display the BGP updates on router C with default weight value.

C #show ip bgp

 Then verify the routes in router C routing table, run the command

C #show ip route 

Now change the weight value on router C in order to give it preference over a lower one. 

In global configuration Mode: 

C(config)# router bgp 20

C (config-router) # neighbor 50.1.1.1 weight 100

Now again run show command to display the BGP updates on router C with weight value 100.

C #show ip bgp

      

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•  Enhanced Interior Gateway Routing Protocol (EIGRP) Configuration

•  Useful Router commands and configuration

•  Standard IP Access Control List

•  Common Frame Relay Configuration

•  Integrated Services Digital Network (ISDN)