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[ScreenOS] Is IPsec traffic being blocked?



Article ID: KB7282 KB Last Updated: 15 Dec 2017Version: 8.0

The dial-up Client is unable to connect to the firewall. Something might be blocking the VPN traffic.


The dial-up client is unable to connect to the firewall. IPsec traffic might be blocked at the client site by the PC's firewall, a router, NAT device, or ISP.



Try the following steps to resolve the issue:

  • If the PC has a personal firewall, temporarily disabling it to check if it is blocking the IPsec traffic.

  • For NAT Traversal to work, UDP port 500, UDP port 4500, and IP Protocol 50 must be allowed through on the router upstream from the Juniper firewall.  The UDP ports are for IKE negotiations and IP Protocol 50 is for the IPsec traffic itself. Make sure that nothing is blocking the ports. You may have to call your ISP to have them unblock them.

  • Enable NAT traversal on both ends of the tunnel.

  • If the network has a Linksys router, check the version of the Linksys router.  Linksys routers had some issues with version  Linksys router version reported successful results, which allows NAT traversal IPsec packets to pass through.

    Note: Ensure that IPsec Passthrough is disabled on the Linksys router.  IPsec Passthrough will break the NAT Traversal functionality.

For more information, refer to KB5671 - What Ports Are Used for a Virtual Private Network (VPN)?

Modification History:
2017-12-07: Article reviewed for accuracy. No changes made. Article is correct and complete.

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