Monday, May 19, 2014

Advertising arbitrary routes via OSPF on Fortigate

To be clear, I'm not sure this is the correct way to inject routes into OSPF. That being said, it yields the desired behavior. The situation goes like this...

I have addressed all of the interfaces of my Fortigate (FGT) with subnets of network Additionally, I have some virtual IPs (VIPs) defined that map addresses from to corresponding addresses in For example: ->

This is not a garden-variety configuration, mapping one public subnet to another. The reasons are complex, involving BGP, portable subnets, multiple data centers. The bottom line, I need the FGT to NAT this traffic.

My initial solution to this problem was static routes. However, this becomes difficult to maintain as the network grows in complexity (we're definitely into that territory). What I want to do is advertise a subnet of via OSPF. In the Fortigate, it's not as easy as saying "inject this subnet into OSPF." My solution, create a loopback interface on the FGT, and redistribute the connected subnet into OSPF.
  1. Create a Loopback network interface, with an address in the subnet you want to advertise. It doesn't seem to make a difference what address you use.
        edit "port-loopback"
            set vdom "root"
            set ip
            set type loopback
            set description "Loopback interface used to provide route for portable addresses."
            set snmp-index 28

  2. Create a prefix-list entry that identifies the loopback subnet.
        edit "connected-to-ospf-v4"
            set comments "Define connected routes to export to OSPF"
                config rule
                    edit 10
                        set prefix
                        unset ge
                        unset le

  3. Create a route-map that uses the prefix list.
        edit "rm-connected-to-ospf"
            set comments "Defines IPv4 connected routes to redistribute to OSPF"
                config rule
                    edit 10
                        set match-ip-address "connected-to-ospf-v4"

  4. Configure OSPF to redistribute connected networks.
            config redistribute "connected"
                set status enable
                set routemap "rm-connected-to-ospf"

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