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This project is used to establish a TCP/UDP port mapping from an ISP NAT public address to local private address. If all layers of NAT are full cones (NAT-1), any host can access internal services through the mapped public address. In bind mode, all traffic does not go through this program.


How to Build

git clone --recursive
cd natmap

# statically link

# cross compile
make CROSS_PREFIX=${cross-toolchain}/bin/x86_64-unknown-linux-

# android
mkdir natmap
cd natmap
git clone --recursive jni

How to Use


 natmap [options]

 -4                  use IPv4
 -6                  use IPv6
 -u                  UDP mode
 -d                  run as daemon
 -i <interface>      network interface or IP address
 -k <interval>       seconds between each keep-alive
 -s <addr>[:port]    domain name or address of STUN server
 -h <addr>[:port]    domain name or address of HTTP server
 -e <path>           script path for notify mapped address
 -f <mark>           fwmark value (hex: 0x1, dec: 1, oct: 01)

Bind options:
 -b <port>           port number for binding

Forward options:
 -T <timeout>        port forwarding timeout in seconds
 -t <address>        domain name or address of forward target
 -p <port>           port number of forward target (0: use public port)

Bind mode

natmap -s -h -b 80

natmap -u -s -b 443

In TCP mode, this program will establishs a TCP port mapping in two steps:

  1. Establish a connection with the HTTP server from the specified bind port and keep it alive.
  2. Establish a connection with the STUN server from the same port and obtain the public address.

This program will then call the script specified by the argument to inform the public address after the port mapping is established. The script can update the DNS record for external access.

Please note that you need to open the firewall to allow access to the bind port.


Goto Network -> Firewall -> Traffic Rules

Add a traffic rule:

  • Protocol: TCP/UDP
  • Source zone: wan
  • Destination zone: Device (input)
  • Destination port: [bind port]
  • Action: accept
  • Others: keep default values

If the port binding fails because it is already in use, this program will try to find out which local service process occupies the port and enable port reuse remotely. This works in Linux kernel 5.6 and later, and needs to run as root.

Forward mode

natmap -s -h -b 80 -t -p 80

natmap -u -s -b 443 -t -p 443

Similar to bind mode, this program will listen on bound port, accepts incoming connections, and forward them to target address.

Another way is to use firewall's DNAT to forward, and this way should uses bind mode.


Goto Network -> Firewall -> Port Forwards

Add a port forward rule:

  • Protocol: TCP/UDP
  • Source zone: wan
  • External port: [bind port]
  • Destination zone: lan
  • Internal IP address:
  • Internal port: 80
  • Others: keep default values

Script arguments

{public-addr} {public-port} {ip4p} {private-port} {protocol} {private-addr}
  • argv[0]: Script path
  • argv[1]: Public address (IPv4/IPv6)
  • argv[2]: Public port
  • argv[3]: IP4P
  • argv[4]: Bind port (private port)
  • argv[5]: Protocol (TCP/UDP)
  • argv[6]: Private address (IPv4/IPv6)

IP4P address

The IP4P address format uses IPv6 special addresses to encode IPv4 addresses and ports for easy distribution through DNS AAAA records.