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Part 1: 5 BGP commands rarely used

Today we are going to talk about some of the BGP commands which actually very rare people know to use. 

In this article, we will talk about that 5 commands and we will come up others in our next article. The main purpose of these commands and how to configure in the network when you enabled BGP.

Fig 1.1- BGP basic connectivity


Command No1: "bgp bestpath as-path ignore"

You may heard about this command but did you know what is the purpose of this command in actual ?

This command is used to prevent the router from considering as-path as a factor in the algorithm for choosing a route, use the "bgp bestpath as-path ignore" router configuration command. To allow the router to consider as-path in choosing a route, use the no form of this command.

R1(config)# router bgp 100
R1(config-router)# bgp bestpath as-path ignore

Command No2: bgp bestpath missing-as-worst

So our second command which we are going to discuss is "bgp bestpath missing-as-worst". The purpose of this command is to consider a missing MED attribute in a path as having a value of infinity, making the path without a MED value the least desirable path, use the bgp bestpath missing-as-worst router configuration command. 

To return the router to the default (assign a value of 0 to the missing MED), use the no form of this command.

R1(config)# router bgp 100
R1(config-router)# bgp best path med missing-as-worst

Command No3: bgp client-to-client reflection

Let's talk about the third one now, This command is used to restore route reflection from a BGP route reflector to clients, use the "bgp client-to-client reflection" router configuration command. 

Here we used this command to disables route reflection between two neighbors that are fully meshed

R1(config)# router bgp 100
R1(config-router)# neighbor 120.120.120.11 route-reflector-client
R1(config-router)# neighbor 120.120.120.11 route-reflector-client
R1(config-router)# neighbor 120.120.120.11 route-reflector-client
R1(config-router)# no bgp client-to-client reflection

Command No4: bgp default local-preference

So here we are with command number 4 which is "bgp default local-preference" and is used to change the default local preference value, use the bgp default local-preference router configuration command. To return to the default setting, use the no form of this command.

R1(config)#router bgp 100
R1(config-router)#bgp default local-preference 500 

Command No5: bgp fast-external-fallover

The last command which we are going to discuss here is "bgp fast-external-fallover" and is used to immediately reset the BGP sessions of any directly adjacent external peers if the link used to reach them goes down, use the bgp fast-external-fallover router configuration command. To disable this function, use the no form of this command.

R1(config-if)#router bgp 100
R1(config-router)#no bgp fast-external-fallover