COMPUTER TIPS

How to configure BGP with local preference attribute?

 

 

IBGP stands for Internal Border Gateway Protocol use local preference attribute to propagate the IBGP traffic to other autonomous systems. We use local preference attribute in IBGP, if there are multiple exit path are available from local autonomous system to destination. 

The default value of local preference is 100 and the range is from 0 to 4294967295. If we change the local preference value of one router that change will propagate to all other routers in same autonomous system and the route with maximum local preference value will be considered as the best route. 

We will configure here only local preference attribute in detail and the remaining attributes will be discussed in the next tips. 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 EBGP and IBGP. At the end, we will change the local preference 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 local preference value.

C #show ip bgp

D #show ip bgp

Now change the local preference value on router B (exit point router) in order to give it preference over a lower one. 

In global configuration Mode: 

B(config)# router bgp 20

B (config-router) # bgp default local-preference 400

Now again run show command to display the BGP updates on C and D router to verify the best exit path after changing the local preference 400.

C #show ip bgp 

D #show ip bgp

      

Suggested Reading

•  Break or recover the router password

•  Routing Information Protocol (RIP) Configuration

•  Point-To-Point Leased Line Implementation

•  How to configure Stub area in OSPF protocol?

• How to configure site-to-site VPN tunnel using ASA? New

•  Router basic Troubleshooting Tips

• How to protect EIGRP router from receiving unsigned routing updates?

 

• How to configure BGP with local preference attribute? New

• How to configure Totally Stub Area in OSPF protocol?

• How to configure BGP between two different autonomous systems?

• How to configure virtual link between different areas in OSPF?

• How to perform unequal-cost load balancing using EIGRP?

•  How to configure Site-to-Site IPsec VPN?

• How configure EIGRP authentication to prevent unauthorized   access?

• How to configure BGP with weight attribute?

•  How to configure OSPF step by step?

• How to perform configuration and convergence between RIP and IGRP protocols?

•  How to configure OSPF with multiple areas?

 

•  Interior Gateway Routing Protocol (IGRP) Configuration

•  Extended IP Access Control List

•  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)