Technical Tip: BGP - default-originate-routemap purpose

[dbabic]

Description
This article explains how in scenario, when you are advertising default-route (0.0.0.0/0) with command “#set capability-default-originate enable”, you want to change some parameters of this route before sending it to neighbor.
Most of the time, you would prepend as-path. For route advertised like this, standard route-map that you are using for all advertised prefixes will not work.

Solution
Diagram:

FGT1 < eBGP > FGT2

From FGT2 you are sending prefixes to FGT1 including default-route. You want to prepend as-path to all routes leaving FGT2.


FGT2 (root) # show router bgp

#config router bgp
set as 65000
set router-id 2.2.2.2
config neighbor
edit "10.109.16.85"
set capability-default-originate enable
set soft-reconfiguration enable
set remote-as 65001
set route-map-out "prepend_all"
next
end
config network
edit 1
set prefix 2.2.2.2 255.255.255.255
next
end
end

FGT2 (root) # show router route-map

#config router route-map
edit "prepend_default_route"
config rule
edit 1
set match-ip-address "default_route_only"
set set-aspath "65000 65000"
next
end
next
edit "prepend_all"
config rule
edit 1
set match-ip-address "any_prefix"
set set-aspath "65000 65000 65000 65000"
next
end
next
end

FGT2 (root) # show router prefix-list

#config router prefix-list
edit "any_prefix"
config rule
edit 1
set prefix any
unset ge
unset le
next
end
next

Status on FGT1:

FGT1 # get router info bgp neighbors 10.109.16.62 received-routes
BGP table version is 9, local router ID is 1.1.1.1
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal
Origin codes: i - IGP, e - EGP, ? - incomplete

   Network          Next Hop            Metric LocPrf Weight RouteTag Path
*> 0.0.0.0/0        10.109.16.62                           0        0 65000 i <-/->
*> 2.2.2.2/32       10.109.16.62                           0        0 65000 65000 65000 65000 65000 i <-/->

Total number of prefixes 2

Subnet 2.2.2.2 is received with correct as-path, but default-route not. Solution is to use option “default-originate-routemap” that will appear in cli only if capability-default-originate is enabled.


FGT2 (root) # show router prefix-list

#config router prefix-list
edit "default_route_only"
config rule
edit 1
set prefix 0.0.0.0 0.0.0.0
unset ge
unset le
next
end
next
end

FGT2 (root) # show router route-map

#config router route-map
edit "prepend_default_route"
config rule
edit 1
set match-ip-address "default_route_only"
set set-aspath "65000 65000"
next
end
next

FGT3 (root) # show router bgp

#config router bgp
set as 65000
set router-id 2.2.2.2
config neighbor
edit "10.109.16.85"
set capability-default-originate enable
set soft-reconfiguration enable
set default-originate-routemap "prepend_default_route" <<<<
set remote-as 65001
set route-map-out "prepend_all"
next
end

Status on FGT1 now:

FGT1 # get router info bgp neighbors 10.109.16.62 received-routes
BGP table version is 9, local router ID is 1.1.1.1
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal
Origin codes: i - IGP, e - EGP, ? - incomplete

   Network          Next Hop            Metric LocPrf Weight RouteTag Path
*> 0.0.0.0/0        10.109.16.62                           0        0 65000 65000 65000 i <-/->
*> 2.2.2.2/32       10.109.16.62                           0        0 65000 65000 65000 65000 65000 i <-/->

Total number of prefixes 2