Symptoms:

• Cannot set up a L2TP/IPSec VPN from Microsoft Windows Vista (TM) to X-family

Facts:

• 3CRTPX505-73
• 3CRTPX505-96
• 3CRTPX506-96
• 3CRX506-96
• 3CRTPX5-25-96
• 3CRTPX5-U-96
• TippingPoint
• L2TP
• IPSec
• VPN
• Microsoft Windows Vista (TM)
• X505
• X506
• X5
• 2.5.0
• 2.5.1

Causes: For compliance with export legislation, X-family devices leave the factory supporting only encryption levels below 64 bits. Microsoft Windows Vista (TM) enforces a higher level of IPSec encryption for L2TP VPN connections and so rejects the encryption level offered by the X-family.

Fixes: Install the high encryption software upgrade package on the X-family device. This will enable support for encryption up to 256 bits. Create a new IKE Proposal for 3DES encryption and edit the Default IPSec SA so that it uses the 3DES IKE Proposal.

Here is an example of a common IKE proposal using 3DES that works with the default Windows Vista settings:

1. Select VPN → IPSEC Proposals
2. Click on Create IKE Proposals
3. Define the IKE proposal parameters as follows (This is just a common 3DES example):

• IKE Phase 1 Setup:

Proposal Name: 3DES-SHA1-PSK
Encryption: 3DES-CBC
Integrity: SHA-1
Diffie-Hellman Group: 2 (1024 bits)
Lifetime: 28800
Authentication Type: Pre-Shared Key
IKE Phase 2 Setup:
Encryption: ESP-3DES-CBC
Integrity: ESP-SHA1-HMAC
Lifetime: 3600
Enable Perfect Forward Secrecy   (Leave the checkbox unchecked)   
Diffie-Hellman Group: 2 (1024 bits)

• Product(s): TippingPoint, X Family
• Sub Product(s): X505, X506, X5

— David Gonzalez 2021/04/08 09:45