Absolutely! You don't need a separate TUN device for each user—a single TUN interface can easily handle the entire 10.0.0.0/8 IP range with the right setup. Here's how to make this work, tailored to your specific scenario:

1. Understand Why a Single TUN Works #

TUN devices are layer 3 virtual interfaces that operate on raw IPv4/IPv6 packets—they don't tie to a single IP address. As long as your server writes the user's raw IPv4 packets (with their unique 10.x.x.x source IP) into the TUN device, the kernel's network stack will process them regardless of the source IP, as long as routing and forwarding rules are configured correctly.

2. Set Up the Single TUN Device #

First, create and configure your single TUN interface:

# Create the TUN device (replace "your_user" with the user running your server app)
ip tuntap add dev tun0 mode tun user your_user

# Bring the interface up
ip link set tun0 up

3. Configure System Routing & Forwarding #

To ensure the server forwards traffic from the TUN device out through eth0:

• Enable IP forwarding (required for any routing between interfaces):

  echo 1 > /proc/sys/net/ipv4/ip_forward
  

• Add a route to direct traffic from the 10.0.0.0/8 range through eth0 (if not already handled by default routes):

  ip route add 10.0.0.0/8 dev eth0
  

4. Update Your Server Application #

Modify your server code to write all users' raw IPv4 packets into the same tun0 device instead of creating a new TUN per user. Since TUN is a character device, you can open it once at server startup and reuse that file descriptor for all incoming user traffic.

5. Handle NAT (If Needed) #

Since 10.0.0.0/8 is a private IP range, external networks won't route traffic back to these addresses directly. Use iptables to set up masquerading (SNAT) so outgoing traffic uses your server's public IP on eth0:

iptables -t nat -A POSTROUTING -s 10.0.0.0/8 -o eth0 -j MASQUERADE

Key Benefits of This Approach #

• Simpler management: No need to create/destroy TUN devices as users connect/disconnect.
• Better scalability: A single TUN can handle hundreds (or thousands) of users, as long as your server has enough CPU/memory to process the traffic.
• Cleaner network stack: Avoid cluttering your system with dozens of unused TUN interfaces.

备注：内容来源于stack exchange，提问作者Ali Khazaee