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[ScreenOS] How to enable the Optimized feature of VPN Monitor and what does it do



Article ID: KB9522 KB Last Updated: 17 Feb 2021Version: 8.0

This article provides information on how to enable the Optimized feature of VPN Monitor and about its functionality.

When enabling optimization, existing traffic via the VPN is used for the monitoring packet, instead of using the VPN monitor ping, which would normally be sent. How is Optimization enabled and how is it used?

To enable the Optimized feature of VPN Monitor:


  1. Select VPNs > AutoKey IKE.
  2. Find the AutoKey IKE for the tunnel in question and click Edit.
  3. Click the Advanced button.

    The VPN Monitor configuration is at the bottom of the page. The Optimized feature is enabled with a check box:
For information on Source Interface and Destination IP, refer to KB9503 - Configuring the Source Interface and Destination IP options of VPN Monitor  


Type the following command:
set vpn <vpnname> monitor optimized [rekey]


What is the Optimized feature used for?

When you enable VPN monitoring for a specific tunnel, the security device sends ICMP echo requests (or pings) via the tunnel at specified intervals (configured in seconds) to monitor network connectivity through the tunnel.  For information on configuring the VPN monitor time and threshold, refer to KB3988 - How does VPN monitor detect the VPN is up or down?

When Optimized is selected, the VPN monitoring behavior changes as follows:

  • The Juniper firewall device accepts incoming traffic through the VPN tunnel as a substitute for ICMP echo replies.
  • If there is both incoming and outgoing traffic through the VPN tunnel, the device suppresses VPN monitoring pings.
  • If you enable VPN monitoring optimization, be aware that VPN monitoring can no longer provide accurate SNMP statistics.

Note: If you upgrade from ScreenOS 4.x to ScreenOS 5.x and find that the VPN tunnels are marked as down by the VPN monitor, it is recommended to enable the Optimized feature of VPN Monitor.

Modification History:
2021-02-07: Added relevant KB links related to VPN monitoring.
2019-05-28: Solution section restored.  In the prior version, the solution section was empty.

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