Technical Tip: How to change the parameters of a BGP route advertised using capability-default-originate

[ppatel]

Description
This article describes how in scenario, when default-route is advertising (0.0.0.0/0) with command 'set capability-default-originate enable', change some parameters of this route before sending it to neighbor.
Most of the time, prepend as-path.

For route advertised like this, standard route-map that used for all advertised prefixes will not work.

---

Setup.

FGT1 < eBGP > FGT2

FGT2 is sending prefixes to FGT1 including default-route.
Now it is possible to prepend as-path to all routes leaving FGT2.


Solution

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

   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

   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 2reference