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[ScreenOS] How do I create a LAN to LAN VPN using preshared secrets to a site with a Dynamically assigned IP address? (ScreenOS 6.0 and later)

  [KB15076] Show Article Properties


Summary:
Policy-based VPN - One Side has a Dynamic IP using Pre-shared Keys in ScreenOS 6.x
Symptoms:
Environment:
  • Preshared secrets
  • Policy Based VPN
  • Static IP Addresses on' one one gateway
  • Dynamically assigned IP address on one gateway
Solution:


This example assumes:

  • A static IP address is assigned to site A
  • Site B gets its IP address dynamically via DHCP.
  • The preshared secret used is netscreen.

The matrix below shows the proposals that are used in this example:

Site A B
Untrust IP of Firewall 1.1.1.1  (eth0/0) DHCP (local id siteb.netscreen.com)
Trust Network 10.1.1.0/24 172.16.10.0/24
Phase 1 Proposal pre-g2-3des-sha pre-g2-3des-sha
Phase 2 Proposal g2-esp-3des-sha g2-esp-3des-sha

Site A:

  1. Click VPNs > AutoKey Advanced > Gateway
  2. Click New
    1. Gateway Name: Site B GW
    2. Remote Gateway: Click Dynamic IP Address, and enter peer id siteb.netscreen.com
    3. Click Advanced
    4. Preshared Key: netscreen
    5. Outgoing Interface: ethernet0/0 (or whichever interface goes out to the Internet)
    6. Security Level, User-Defined:  Select Custom, and select Phase 1 Proposal: pre-g2-3des-sha
    7. Mode (Initiator): Aggressive
    8. Click Return
  3. Click OK
  4. Click VPNs > Autokey IKE
  5. Click New
    1. VPN Name: Site B VPN
    2. Remote Gateway: Click Predefined, and select Site B GW from the pulldown menu
    3. Click Advanced
    4. Security Level, User-Defined: Custom, and select Phase 2 Proposal: g2-esp-3des-sha
    5. Click Return
  6. Click OK   (Important)
  7. Click Policy > Policies
  8. Select From Trust to Untrust Zone, and click New
    1. Source Address: Click New Address, and enter 10.1.1.0/24
    2. Destination Address: Click New Address, and enter 172.16.10.0/24
    3. Service: Any
    4. Action: Tunnel
    5. Tunnel: Site B VPN
    6. Click Modify matching bidirectional VPN policy
    7. Click Position at Top
  9. Click OK

Site B:

  1. Click VPNs > AutoKey Advanced > Gateway
  2. Click New
    1. Gateway Name: Site A GW
    2. Remote Gateway: Click Static, and enter IP address 1.1.1.1
    3. Click Advanced
    4. Preshared Key: netscreen
    5. Local ID: siteb.netscreen.com
    6. Outgoing Interface: ethernet0/0 (or whichever interface goes out to the Internet)
    7. Security Level, User-Defined: Select Custom, and select Phase 1 Proposal: pre-g2-3des-sha
    8. Mode (Initiator): Aggressive
    9. Click Return
  3. Click OK
  4. Click VPNs > Autokey IKE
  5. Click New
    1. VPN Name: Site A VPN
    2. Remote Gateway: Click Predefined, and select Site A GW from the pulldown menu
    3. Click Advanced
    4. Security Level, User-Defined:  Custom and select Phase 2 Proposal: g2-esp-3des-sha
    5. Click Return
  6. Click OK
  7. Click Policy > Policies
  8. Select From Trust to Untrust Zone, and click New
    1. Source Address: Click New Address, and enter 172.16.10.0/24
    2. Destination Address: Click New Address, and enter 10.1.1.0/24
    3. Service: Any
    4. Action: Tunnel
    5. Tunnel: Site A VPN
    6. Clic Modify matching bidirectional VPN policy: Enabled
    7. Click Position at Top
  9. Click Ok

 

NOTE:
The VPN tunnel must be initiated from a host behind the gateway with the dynamically assigned IP address. This requires sending any traffic from a host behind the Juniper firewall that has its IP address assigned dynamically. Otherwise, the VPN tunnel will not be built.



If you followed the steps above, and now you need help troubleshooting, refer the VPN Configuration & Troubleshooting Guide.
Modification History:
2017-12-23: Article reviewed for accuracy. Tagged the article as ScreenOS in title. Article is correct and complete.
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