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This article describes the use of Virtual IP to redistribute in BGP to advertise to other BGP peers.
It is helpful in scenarios where the VIP IP is out of the subnet range of exit interface subnet/peer.

BGP is setup and peering is up between 2 units.
VIP range or VIP is configured and policies configured for VIP to work.

BGP requires the network to be known in the network table to advertise to its peer, which does not happen in case of VIP (with different subnet than exit interface IP) as virtual IP does not show in network routing table.

Since this is impossible to redistribute such Virtual IP in BGP, create a static black hole route and redistribute static route in the BGP as per below:
VIP subnet : is configured on 'FGT1'.
Exit interface IP is
This subnet is required to be advertised to BGP peer so the VIP IP is reachable from remote 'FGT2'.

Configuration Steps.

# config router static
    edit 0
        set dst
        set blackhole enable
# config router bgp
    # config redistribute "static"

        set status enable
'FGT2' no config changes is required as the route will be advertised from 'FGT1' BGP peer.

Verification command.
FGT1# get router info routing de
Routing table for VRF=0
Routing entry for
  Known via "static", distance 10, metric 0, best
  * directly connected, Null
FGT1 # get router info bgp neighbors advertised-routes
VRF 0 BGP table version is 7, local router ID is
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
*>i10.56.240.0/22                     100  32768        0 ? <-/->
*>i10.80.1.0/24                   100  32768        0 i <-/->
*>i10.98.8.0/24                   100  32768        0 ? <-/->

FGT2(root) # get router info routing de bgp
B [200/0] via, port4, 00:31:10

FGT2(root) # get router info bgp network

BGP routing table entry for
Paths: (1 available, best #1, table Default-IP-Routing-Table)
  Not advertised to any peer
  Local from (
      Origin incomplete metric 0, localpref 100, valid, internal, best
      Last update: Thu Aug  6 10:20:48 2020

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Configuration Example: Using VIP (Virtual IP) for Port Translation only