Understanding BGP Backdoor – IP With Ease

In additional continuation to our dialogue on BGP associated phrases and methodologies, on this publish we are going to focus on using BGP backdoor method and corresponding configuration on BGP audio system.

What’s BGP Backdoor?

BGP Backdoor is a well known function of BGP to change the administrative distance of exterior Border Gateway Protocol (eBGP) to provide priority to an inner gateway routing protocol (IGP) over an eBGP route. By default, exterior BGP (eBGP) is assigned an administrative distance of 20.

Administrative distance is the foremost criterion which a router considers when it has to decide on between two routing protocols that present route data for a similar vacation spot. This administrative distance is a scale which signifies how dependable and reliable the supply of the route data is. A decrease administrative distance worth displays that the protocol/hyperlink is extra reliable.

The “Backdoor Function” can be utilized to up the executive distance of eBGP to 200 to guarantee that IGP realized routes are given precedence. This function implies that a backdoor community will probably be handled like a neighborhood one, nevertheless, it is not going to be marketed. This may be accomplished by utilizing the community BGP backdoor command.

Topology to Perceive BGP Backdoor

As per topology now we have three routers R1, R2 & R3 having IGP/BGP configured in following style –

R1 <-> R2 OSPF
R2 <-> R3 EBGP
R1 <-> R3 EBGP

Each R1 and R3 obtain the route R2 loopback (9.9.0.2)  from Router R2 by way of OSPF and eBGP respectively.R1 and R3 additional have an EBGP neighborship and therefore R1 will obtain the route of 9.9.0.2 from R3 by way of eBGP. Now R1 has two routes for 9.9.0.2, one from R2 by way of OSPF and one other from R3 by way of eBGP.

Because the eBGP learnt route AD is 20 and OSPF being 110, eBGP route by way of R3 is the popular one and put in within the routing desk. Nevertheless, contemplating shortest path we received’t favor to achieve to 9.9.0.2 by way of path R1 > R3 >R2 since now we have much less hop path i.e. R1>R2.

As a way to obtain this there have 2 two choices:

1: Change the eBGP AD worth to a worth bigger than AD 110 of OSPF

2: Use the BGP backdoor command.

Choice 1 of adjusting the AD worth is much less beneficial therefore mostly used technique to realize this required output is Choice 2 i.e. to make use of of BGP backdoor command.

Now lets us check out the working and configurations of our topology:

CONFIGURATION 

R1:

R2:

R3:

VERIFICATION

Checking route of R2s loopback on R1 with out BGP backdoor.

After the BGP backdoor is configured on R1 as follows: 

Verifying the route for 9.9.0.2 now on R1: 

Proceed Studying:

BGP Multipath As-Path Chill out

BGP Origin Attribute