Technical Tip: Using the IPSec auto-negotiate and keepalive options on IPsec VPN tunnel
Description
This article describes the use of auto-negotiate and keepalive options under IPsec VPN phase2 settings.
Scope
FortiGate.
Solution
The option below can be used if there is no interesting traffic towards the tunnel. However, if there is interesting traffic towards the tunnel, the tunnel negotiation will occur automatically.
- Autokey Keep Alive: Enable the option to keep the tunnel active when no data is being processed.
The Phase-2 SA has a fixed duration. If there is traffic on the VPN as the SA nears expiry, a new SA is negotiated and the VPN switches to the new SA without interruption.
However, if there is no traffic, the SA expires (by default) and phase-2 goes down. A new SA will not be generated until there is traffic.
The Autokey Keep Alive option ensures that a new Phase 2 SA is negotiated, even if there is no traffic, so the VPN tunnel stays up.
- Auto-negotiate: Enable the option to automatically renegotiate the tunnel when the tunnel expires.
By default, the phase 2 security association (SA) is not negotiated until a peer attempts to send data. The triggering packet and some subsequent packets are dropped until the SA is established.
Applications normally resend this data, so there is no loss, but there might be a noticeable delay in response to the user.
If the tunnel goes down, the auto-negotiate feature (when enabled) attempts to re-establish the tunnel.
Auto-negotiate initiates the phase-2 SA negotiation automatically, repeating every five seconds until the SA is established.
Automatically establishing the SA can be important for a dial-up peer. It ensures that the VPN tunnel is available for peers at the server end to initiate traffic to the dial-up peer.
If auto-negotiation is enabled at both FortiGates, either side can renegotiate the phase 2 security association (SA) to keep the IPsec VPN tunnel active. Hence, enabling auto-negotiation at both ends would be a good practice.
Auto-negotiation is necessary when setting up the tunnel for the first time, as the absence of traffic might prevent Phase 2 from being initiated. This requirement also applies to Site-to-Site tunnels.
Otherwise, the VPN tunnel does not exist until the dial-up peer initiates traffic.
To configure auto-negotiate:
Policy-based IPsec VPN.
config vpn ipsec phase2
edit <phase2_name>
set auto-negotiate enable
set keepalive enable
next
end
Route-based IPsec VPN.
config vpn ipsec phase2-interface
edit <phase2_name>
set auto-negotiate enable
set keepalive enable
next
end
To configure via GUI:
Auto-negotiation and keepalive are disabled by default on the FortiGate. However, keepalive gets implicitly enabled once auto-negotiation is enabled.
Refer below to configure Auto-negotiation and keepalive settings in v7.6 via GUI:
Note:
In v7.6, the keepalive options become visible after editing the individual selector within Phase2.
CLI Troubleshooting.
diagnose sniffer packet any ' port 500 or port 4500 ' 4 0 l
Note:
- Auto-negotiation cannot be enabled in the case of a Dial-up IPsec VPN tunnel because, in this scenario, the FortiGate can never be the initiator. The ISAKMP or IKE requests are always initiated from the user end when trying to connect.
- In the tunnel where the device is in passive mode, auto-negotiate and autokey-keepalive in phase 2, and auto-negotiate in phase 1 cannot be enabled in phase 2. The device that is acting as an IKE initiator should be enabled for auto-negotiation.
To justify, the tunnel has been created between two FortiGate devices. The tunnel is configured with the following Phase 1 and Phase 2 settings:
PHASE-1:
FGVM04TM25002496 # config vpn ipsec phase1-interface
FGVM04TM25002496 (phase1-interface) # ed 51.46_spoke
FGVM04TM25002496 (51.46_spoke) # sh
path=vpn.ipsec, objname=phase1-interface, tablename=51.46_spoke, size=2960
config vpn ipsec phase1-interface
edit "51.46_spoke"
set interface "port1"
set ike-version 2
set peertype any
set net-device disable
set passive-mode enable ---> The passive mode is enabled.
set proposal aes128-sha256 aes256-sha256 aes128gcm-prfsha256 aes256gcm-prfsha384 chacha20poly1305-prfsha256
set comments "VPN: 51.46_spoke"
set remote-gw 10.40.51.46
set psksecret ENC O7xCYc7Zm1VL/kIBgWbGK+uAG1Seb8xdh0I4YUhIOA6za8sQ/9kyFh41OoGzndL3ysZzGP//Eytw8vlX6UOYcAXJCdCAxZxgZZDDp9hunI/ZtxvL
next
end
PHASE-2:
FGVM04TM25002496 (phase2-interface) # ed 51.46_spoke
FGVM04TM25002496 (51.46_spoke) # sh
path=vpn.ipsec, objname=phase2-interface, tablename=51.46_spoke, size=680
config vpn ipsec phase2-interface
edit "51.46_spoke"
set phase1name "51.46_spoke"
set proposal aes128-sha1 aes256-sha1 aes128-sha256 aes256-sha256 aes128gcm aes256gcm chacha20poly1305
set pfs disable
set comments "VPN: 51.46_spoke "
set src-addr-type name
set dst-addr-type name
set src-name "51.46_spoke_local"
set dst-name "51.46_spoke_remote"
next
end
Going forward, change the passive mode from Enable to Disable and set Auto-Negotiation.
FGVM04TM25002496 (51.46_spoke) # set passive-mode dis
path=vpn.ipsec, objname=phase1-interface, size=2960, sz_attr=1
FGVM04TM25002496 # config vpn ipsec phase2-interface'
FGVM04TM25002496 (phase2-interface) # edit 51.46_spoke
change table entry '51.46_spoke'
FGVM04TM25002496 (51.46_spoke) # set auto-negotiate
enable Enable setting.
disable Disable setting.
FGVM04TM25002496 (51.46_spoke) # set auto-negotiate enable
path=vpn.ipsec, objname=phase2-interface, size=680, sz_attr=1
FGVM04TM25002496 (51.46_spoke) # end
cmd_clean_context 0, abort=0
After applying the changes:
FGVM04TM25002496 (51.46_spoke) # show full-configuration
path=vpn.ipsec, objname=phase1-interface, tablename=51.46_spoke, size=2960
config vpn ipsec phase1-interface
edit "51.46_spoke"
set type static
set interface "port1"
set ip-version 4
set ike-version 2
set local-gw 0.0.0.0
set keylife 86400
set authmethod psk
unset authmethod-remote
set peertype any
set monitor-min 0
set net-device disable
set passive-mode disable ---> The Passive mode is disabled.
next
end
FGVM04TM25002496 # config vpn ipsec phase1-interface
FGVM04TM25002496 (phase1-interface) # set pass ---> It will not be able to enable the passive mode.
command parse error before 'set'
Related documents:
Troubleshooting Tip: Troubleshooting IPsec Site-to-Site Tunnel Connectivity