Technical Tip: Fortinet Auto Discovery VPN (ADVPN) with RIP Version 2

akileshc · ‎09-23-2020

Description
This article describe how to configure and verify of Auto Discovery VPN (ADVPN) with RIPv2.

Solution
- Fortinet Auto Discovery VPN (ADVPN) allows to dynamically establish direct tunnels (called shortcuts) between the spokes of a traditional Hub and Spoke architecture.
- After a shortcut tunnel is established between two spokes and routing has converged, spoke to spoke traffic no longer needs to flow through the Hub. Direct connectivity is provided.
- ADVPN requires the use of dynamic routing in order to function and supports both BGP and RIPv2. This recipe will focus on using RIP v2 and its route-reflector mechanism as the dynamic routing solution to use with ADVPN.
- ADVPN’s primary advantages is that it provides the full meshing capabilities to a standard hub and spoke topology, greatly reducing the provisioning effort required for full spoke to spoke low delay reachability and addressing the scalability issues associated with very large fully meshed VPN networks.

Diagram.

Configuration.

HUB:

ADVPN Tunnel Configuration.

# config vpn ipsec phase1-interface
    edit "ADVPN"
        set type dynamic
        set interface "port1"
        set peertype any
        set net-device disable
        set proposal aes128-sha1
        set add-route disable
        set dpd on-idle
        set dhgrp 2
        set auto-discovery-sender enable
        set tunnel-search nexthop
        set psksecret ENC
        set dpd-retryinterval 60
    next

# config vpn ipsec phase2-interface
    edit "ADVPN-P2"
        set phase1name "ADVPN"
        set proposal aes128-sha1
    next
end

RIPv2.

# config router rip
    # config network
        edit 1
            set prefix 1.1.1.10 255.255.255.255
        next
        edit 2
            set prefix 10.10.10.0 255.255.255.0
        next
    end
    # config interface
        edit "ADVPN"
            set receive-version 2
            set send-version 2
            set send-version2-broadcast enable
        next
    end
end

Interface Configuration.

# config system interface
    edit "ADVPN"
        set vdom "root"
        set ip 10.10.10.1 255.255.255.255
        set allowaccess ping
        set type tunnel
        set remote-ip 10.10.10.0 255.255.0.0
        set snmp-index 14
        set interface "port1"
    next
end

Policy.

# config firewall policy
    edit 5
        set name "ADVPNtoADVPN"
        set uuid bf723e6e-19ae-51e9-fde9-2764c6d2fa15
        set srcintf "ADVPN"
        set dstintf "ADVPN"
        set srcaddr "all"
        set dstaddr "all"
        set action accept
        set schedule "always"
        set service "ALL"
        set logtraffic all
        set fsso disable
    next
end
edit 4
        set name "IN ADVPN"
        set uuid aab442e2-19ae-51e9-1fe2-c16613fe003d
        set srcintf "ADVPN"
        set dstintf "port4"
        set srcaddr "all"
        set dstaddr "all"
        set action accept
        set schedule "always"
        set service "ALL"
        set logtraffic all
        set fsso disable
    next
end

# config firewall policy
    edit 3
        set name "OUT ADVPN"
        set uuid 8dfd6d0e-19ae-51e9-ac74-d86a9af57fa0
        set srcintf "port4"
        set dstintf "ADVPN"
        set srcaddr "all"
        set dstaddr "all"
        set action accept
        set schedule "always"
        set service "ALL"
        set logtraffic all
        set fsso disable
    next
end

Spoke1: (Same configuration needs to be done over the spoke2 as well).

Tunnel configuration.

# config vpn ipsec phase1-interface
    edit "ADVPN"
        set interface "port1"
        set peertype any
        set proposal aes128-sha1
        set net-device enable
        set add-route disable
        set dhgrp 2
        set auto-discovery-receiver enable
        set remote-gw 10.5.27.173
        set psksecret ENC
end

# config vpn ipsec phase2-interface
    edit "ADVPN-P2"
        set phase1name "ADVPN"
        set proposal aes128-sha1
        set auto-negotiate enable
    end

RIPv2 configuration.

# config router rip
    # config network
        edit 1
            set prefix 1.1.1.1 255.255.255.255
        next
        edit 2
            set prefix 10.10.10.2 255.255.255.255
        next
    end
    # config interface
        edit "ADVPN"
            set receive-version 2
            set send-version 2
        next
    end
end

Interface Configuration.

# config system interface
    edit "ADVPN"
        set vdom "root"
        set ip 10.10.10.2 255.255.255.255
        set allowaccess ping
        set type tunnel
        set remote-ip 10.10.10.1 255.255.255.255
        set snmp-index 14
        set interface "port1"
    next
end

Policy.

# config firewall policy
edit 5
        set name "IN ADVPN"
        set uuid 471a8b7c-19b0-51e9-bec5-9ac0ee436f1a
        set srcintf "ADVPN"
        set dstintf "port4"
        set srcaddr "all"
        set dstaddr "all"
        set action accept
        set schedule "always"
        set service "ALL"
        set logtraffic all
        set fsso disable
    next
edit 3
        set name "OUT ADVPN"
        set uuid 2ffae662-19b0-51e9-cf68-6d600cd529df
        set srcintf "port4"
        set dstintf "ADVPN"
        set srcaddr "all"
        set dstaddr "all"
        set action accept
        set schedule "always"
        set service "ALL"
        set logtraffic all
        set fsso disable
    next
end

Troubleshooting or verifying.

# di vpn tunnel list
# get router info routing-table rip
# get router info rip database

Notes about ADVPN in FortiOS.

- Auto-discovery is only supported by IKEv1.
- All Spokes must have an IP address that is routable from any other spoke; units behind NAT are not currently supported.
- The feature requires the use of a dynamic routing protocol. There is no support for IKE handling routing.
- RIP is not a very scalable routing protocol. When there are more than a few spokes it would be advisable to use route summarization to avoid huge RIP updates. Better yet, use BGP instead of RIP.
- It is assumed that spokes will not be used to transit other spoke traffic, for example: traffic from Chicago to Tokyo would not transit an existing Chicago to Hong Kong tunnel even though that has a shorter hop count than a route via New York and Shanghai.
- There is no facility to allow to filter which traffic that transits the hub should trigger the message sent to the initiator suggesting it create a direct connection. Currently any and all traffic will trigger it.