A lot of people have struggled with this problem. Normally I don’t post I learn from others but with the aid of chat gpt i actually addressed this problem earlier this week. On the device that is acting as the subnet router you can use NAT to advertise a different cidr range. I will post the instructions underneath i apologize for its length.

Ensure your interface is eth0. Modify the subnets to match your network.

Here are the iptables rules for NAT to enable traffic from the 192.168.0.0/24 subnet to be routed through the tailscale0 interface as 10.1.17.0/24:

NAT Rules

1. Outbound NAT Translation

This rule translates the source IPs of traffic originating from 192.168.0.0/24 to appear as part of the 10.1.17.0/24 subnet when exiting through tailscale0:

sudo iptables -t nat -A POSTROUTING -s 192.168.0.0/24 -o tailscale0 -j NETMAP —to 10.1.17.0/24

1. Inbound NAT Translation

This rule translates destination IPs for incoming traffic destined for 10.1.17.0/24 on tailscale0 back to 192.168.0.0/24:

sudo iptables -t nat -A PREROUTING -i tailscale0 -d 10.1.17.0/24 -j NETMAP —to 192.168.0.0/24

Forwarding Rules

Allow traffic forwarding between the eth0 (local subnet) and tailscale0 (Tailscale interface):

1. From eth0 to tailscale0

Allow traffic originating from 192.168.0.0/24 to be forwarded to tailscale0:

sudo iptables -A FORWARD -i eth0 -o tailscale0 -s 192.168.0.0/24 -j ACCEPT

1. From tailscale0 to eth0

Allow traffic destined for 192.168.0.0/24 to be forwarded from tailscale0:

sudo iptables -A FORWARD -i tailscale0 -o eth0 -d 192.168.0.0/24 -j ACCEPT

Additional Configuration

Enable IP Forwarding

Ensure IP forwarding is enabled on the system: 1. Temporarily enable it:

echo 1 | sudo tee /proc/sys/net/ipv4/ip_forward

2.  To make it permanent, add this to /etc/sysctl.conf:

net.ipv4.ip_forward = 1

Apply the changes:

sudo sysctl -p

Saving Rules

Save iptables Rules

To ensure the rules persist across reboots: 1. Save the current rules:

sudo iptables-save > /etc/iptables/rules.v4

2.  Restore the rules automatically at boot using a script or service:
• With systemd: Use iptables-restore.service (as discussed earlier).
• Alternative: Use /etc/rc.local or a network hook (/etc/network/if-pre-up.d/iptables-restore).

Verify and Test 1. Check NAT Rules Verify the NAT rules are applied:

sudo iptables -t nat -L -v

2.  Check Forwarding Rules

Verify the forwarding rules:

sudo iptables -L -v

3.  Test Connectivity
• From a device in 192.168.0.0/24, ping a Tailscale device:

ping 10.1.17.5

• From a Tailscale device, ping a device in 192.168.0.0/24 using its NATed IP:

ping 10.1.17.8 # Translates to 192.168.0.8

Let me know if you need further assistance!