Technical Tip: BGP distance modification on learned routes from neighbors
Description
This article describes how to modify the distance of iBGP or eBGP routes learned from BGP neighbors.
Scope
FortiGate.
Solution
Consider the following example. There is an eBGP neighborship between two FortiGate devices.
FGT-I.
config router bgp
set as 65101
set router-id 1.1.1.1
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
set router-id 2.2.2.2
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 the 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.
config router bgp
set distance-internal 100
end
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