Technical Tip: BGP distance modification on learned routes from neighbors

[alif]

Description
This article describes how to modify the distance of iBGP or eBGP routes learned from BGP neighbors.

Solution
Consider the following example. There is an eBGP neighborship between two FortiGate devices.

** FGT-I **

# config router bgp
    set as 65101
    # config neighbor
        edit "10.5.20.134"
            set soft-reconfiguration enable
            set remote-as 65102
        next
    end
    # config redistribute "connected"
        set status enable
    end
end

** FGT-II **

# config router bgp
    set as 65102
    # config neighbor
        edit "10.5.19.83"
            set soft-reconfiguration enable
            set remote-as 65101
        next
    end
    # config redistribute "connected"
        set status enable
    end
end

Since connected routes are advertised over BGP peers, FGT-I is learning a BGP route 10.0.0.0/20 from FGT II as shown in routing table below.

FGT-I # get router info routing-table all
B       10.0.0.0/20 [20/0] via 10.5.20.134, wan1, 00:00:04

On FGT-I, the external distance of 50 will be defined as shown below.

# config router bgp
    set distance-external 50
end
end

After making changes, it is advised to perform a soft BGP reset.

FGT-I # execute router clear bgp all soft

The route learned from eBGP peer will be advertised now with a distance of 50.

FGT-I # get router info routing-table all
B       10.0.0.0/20 [50/0] via 10.5.20.134, wan1, 00:00:00

distance-external Distance for routes external to the AS. integer Minimum value: 1 Maximum value: 255 Default: 20 (eBGP)
distance-internal Distance for routes internal to the AS. integer Minimum value: 1 Maximum value: 255 Deafault: 200 (iBGP)

Likewise if a route is learned from an iBGP peer, the default distance is set to a value of 200.
This can be modified to another distance value by 'set distance-internal' under BGP settings.

Related link.
https://docs.fortinet.com/document/fortigate/6.2.3/cli-reference/471620/router-bgp