• titlepage
• table-of-contents
• SonicOS 8
• About SonicOS
  • Working with SonicOS
  • SonicOS Workflow
  • How to Use the SonicOS Administration Guides
  • Guide Conventions
• IPSec VPN Overview
  • About Virtual Private Networks
  • VPN Types
    • IPsec VPN
    • DHCP over VPN
    • L2TP with IPsec
    • SSL VPN
  • VPN Security
    • About IKEv1
    • About IKEv2
    • Mobility and Multi-homing Protocol for IKEv2 (MOBIKE)
    • About IPsec (Phase 2) Proposal
    • About Suite B Cryptography
  • VPN Base Settings and Displays
    • Policies
    • Active Tunnels
    • Down Tunnels
    • Settings
  • IPv6 VPN Configuration
• Site to Site VPNs
  • Planning Site to Site Configurations
  • General VPN Configuration
    • Configuring Settings on the General Tab
    • Configuring Settings on the Network Tab
    • Configuring Settings on the Proposals Tab
    • Configuring Settings on the Advanced Tab
  • Managing GroupVPN Policies
    • Configuring IKE Using a Preshared Secret Key
    • Configuring IKE Using 3rd Party Certificates
    • Downloading a GroupVPN Client Policy
  • Creating Site to Site VPN Policies
    • Configuring with a Preshared Secret Key
    • Configuring with a Manual Key
    • Configuring with a Third-Party Certificate
    • Configuring the Remote SonicWall Network Security Appliance
• VPN Auto Provisioning
  • About VPN Auto Provisioning
    • Defining VPN Auto Provisioning
    • Benefits of VPN Auto Provisioning
    • How VPN Auto Provisioning Works
      • About Establishing the IKE Phase 1 Security Association
      • About Establishing IKE Phase 2 using a Provisioned Policy
  • Configuring a VPN AP Server
    • Starting the VPN AP Server Configuration
    • Configuring VPN AP Server Settings on General
    • Configuring VPN AP Server Settings on Network
    • Configuring Advanced Settings on Proposals
    • Configuring Advanced Settings on Advanced
  • Configuring a VPN AP Client
• Rules and Settings
  • Adding a Tunnel Interface
    • Creating a Static Route for the Tunnel Interface
  • Route Entries for Different Network Segments
  • Redundant Static Routes for a Network
• Advanced
  • Configuring Advanced VPN Settings
  • Configuring IKEv2 Settings
  • Using OCSP with SonicWall Network Security Appliances
    • OpenCA OCSP Responder
    • Loading Certificates to Use with OCSP
    • Using OCSP with VPN Policies
• DHCP over VPN
  • DHCP Relay Mode
  • Configuring the Central Gateway for DHCP Over VPN
  • Configuring DHCP over VPN Remote Gateway
  • Current DHCP over VPN Leases
• L2TP Servers and VPN Client Access
  • Configuring the L2TP Server
  • Viewing Currently Active L2TP Sessions
  • Configuring Microsoft Windows L2TP VPN Client Access
  • Configuring Google Android L2TP VPN Client Access
• AWS VPN
  • Overview
  • Creating a New VPN Connection
  • Reviewing the VPN Connection
    • Configuration on the Firewall
    • Configuration on Amazon Web Services
  • Route Propagation
  • AWS Regions
  • Deleting VPN Connections
• SonicWall Support
  • About This Document

L2TP with IPsec

Layer 2 Tunneling Protocol (L2TP) is a tunneling protocol used to support VPNs or as part of the delivery of services by ISPs. It does not provide any encryption or confidentiality by itself, and because of that lack of confidentiality in the L2TP protocol, it is often implemented along with IPsec. The general process for setting up an L2TP/IPsec VPN is:

1. Negotiate an IPsec security association (SA), typically through Internet key exchange (IKE). This is carried out over UDP port 500, and commonly uses either a shared password (also called pre-shared keys), public keys, or X.509 certificates on both ends, although other keying methods exist.
2. Establish Encapsulating Security Payload (ESP) communication in transport mode. The IP protocol number for ESP is 50 (compare TCP's 6 and UDP's 17). At this point, a secure channel has been established, but no tunneling is taking place.
3. Negotiate and establish L2TP tunnel between the SA endpoints. The actual negotiation of parameters takes place over the SA's secure channel, within the IPsec encryption. L2TP uses UDP port 1701.

When the process is complete, L2TP packets between the endpoints are encapsulated by IPsec. Because the L2TP packet itself is wrapped and hidden within the IPsec packet, no information about the internal private network can be garnered from the encrypted packet. Also, UDP port 1701 does not need to be opened on firewalls between the endpoints, because the inner packets are not acted upon until after IPsec data has been decrypted and stripped, which only takes place at the endpoints.