BGP backdoor route
When implementing BGP there are instances where it is not desirable for eBGP-learned routes to be preferred over Interior Gateway Protocol (IGP)-learned routes. However, because eBGP has an AD of 20, which will take precedence over the AD of any IGP, this will not occur by default.
It is possible to advertise a network using the backdoor keyword like so:
R1(config-router)#network 2.2.2.2 mask 255.255.255.255 backdoor
This will cause the route being advertised by eBGP to have an AD of 200. The eBGP neighbor will see something like this in their BGP table:
R2#show ip route | incl 1.1 B 1.1.1.1 [200/0] via 192.168.23.3, 00:00:10
This allows any IGP-learned route to take precedence since its AD will be lower.
Links:
https://forum.networklessons.com/t/bgp-backdoor-routes/1109/24?u=lagapidis
https://networklessons.com/bgp/bgp-backdoor-routes/#BGP_Backdoor_Configuration