General information on how VPN solutions

General information on how VPN solutions typically handle Network Address Translation (NAT) traversal for remote access scenarios, which may apply to Sangfor's VPN solution as well.

NAT traversal is essential for enabling VPN connections when users are located behind a NAT device (such as a router or firewall) and need to establish a connection to the VPN server over the internet. Here are some common methods that VPN solutions, including Sangfor's, might use to address this challenge:

    NAT-T (NAT Traversal): NAT-T is a standard technique that encapsulates VPN traffic within UDP packets to traverse NAT devices. Most modern VPN solutions support NAT-T, and it's often used in IPSec VPNs to enable communication through NAT gateways.

    UDP Encapsulation: Some VPN solutions use UDP encapsulation to carry VPN packets within UDP datagrams. This technique allows VPN traffic to pass through NAT devices that may block other protocols.

    TCP Port 443 (SSL/TLS VPN): Many VPN solutions, especially SSL/TLS VPNs, use TCP port 443 for communication. Port 443 is commonly used for HTTPS (secure web browsing), and most NAT devices allow outbound traffic on this port to pass through.

    Port Forwarding: VPN servers may require specific ports to be forwarded on the NAT device to allow VPN traffic to reach the VPN server. For example, UDP port 500 and UDP port 4500 are commonly used for IPSec VPNs and may need to be forwarded to the VPN server's internal IP address.

    STUN (Session Traversal Utilities for NAT): VPN clients can use STUN to discover the presence of NAT and determine the public IP address assigned by the NAT device. This information helps establish direct communication with the VPN server.

    UPnP (Universal Plug and Play): If supported by the VPN solution and the NAT device, UPnP can be used to automatically configure port forwarding on compatible routers.

    Relay Servers (TURN): In scenarios where direct communication between the VPN client and server is not possible due to restrictive NAT configurations, VPN solutions might use relay servers (TURN) as intermediaries to relay VPN traffic.

It's important to note that the specific NAT traversal techniques employed by Sangfor's VPN solution may vary based on the product version and configuration options.

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