NAT64 DNS Lookup Example

This example demonstrates how a Contiki-NG IoT node can resolve public domain names and communicate with IPv4 servers through a NAT64-enabled border router.

Overview

The IoT node configures Google Public DNS (8.8.8.8) as its nameserver, encoded as a NAT64 address (64:ff9b::808:808). It then uses the standard Contiki-NG DNS resolver to look up hostnames such as www.contiki-ng.org and www.example.com.

The border router’s NAT64 module intercepts the DNS queries, translates them from IPv6 to IPv4, and forwards them to 8.8.8.8 via a host UDP socket. Responses are translated back with DNS64 synthesis: A records (IPv4 addresses) become AAAA records with the 64:ff9b::/96 prefix.

After each successful lookup, the node sends a UDP probe to the resolved address to demonstrate end-to-end connectivity to the IPv4 internet.

Testing with Cooja (no hardware needed)

1. Start the Cooja simulation

Open nat64-dns-cooja.csc in Cooja. The simulation contains:

Mote 1 — SLIP radio bridge (connects Cooja to the native border router)
Mote 2 — NAT64 DNS client (the example application)

Start the simulation. Cooja will listen on TCP port 60001 for the border router to connect.

2. Start the native border router with NAT64

In a separate terminal:

cd examples/nat64
sudo ./run-nat64-br.sh

This builds and starts the native border router, which connects to Cooja on localhost:60001 and enables the NAT64 gateway.

3. Observe the output

In Cooja’s log listener, mote 2 will show:

NAT64 DNS client starting, waiting for network...
DNS server set to 64:ff9b::808:808 (8.8.8.8 via NAT64)
Querying DNS for "www.contiki-ng.org"...
Resolved "www.contiki-ng.org" -> 64:ff9b::b63c:d8a7
Sent UDP probe to 64:ff9b::b63c:d8a7 (www.contiki-ng.org)

Running on real hardware

1. Build and flash the DNS client on the sensor node

cd examples/nat64
make TARGET=<your-target>

Replace <your-target> with the platform of your sensor node (e.g., nrf, cc2538dk, zoul).

Flash the resulting binary onto the node. Then flash the border router firmware from examples/rpl-border-router onto a second node that will serve as the 802.15.4 radio interface for the native border router.

2. Start the native border router with NAT64

cd examples/nat64
sudo ./run-nat64-br.sh /dev/ttyUSB0

Replace /dev/ttyUSB0 with the serial port of the radio interface node. Without an argument, the script falls back to connecting to Cooja on localhost:60001.

How It Works

IoT node                    Border router (native)          Internet
   |                              |                            |
   |-- DNS query (IPv6/UDP) ----->|                            |
   |   to 64:ff9b::808:808       |-- DNS query (IPv4/UDP) --->|
   |                              |   to 8.8.8.8              |
   |                              |                            |
   |                              |<-- DNS response (A rec) ---|
   |<-- DNS response (AAAA) -----|   (DNS64 synthesis)        |
   |   64:ff9b::<ipv4>           |                            |
   |                              |                            |
   |-- UDP probe (IPv6) -------->|                            |
   |   to 64:ff9b::<ipv4>        |-- UDP probe (IPv4) ------->|
   |                              |   to <ipv4>               |

Files

nat64-dns-client.c — The example application.
project-conf.h — Configuration: DNS cache size, MDNS disabled.
Makefile — Includes the resolv module.
nat64-dns-cooja.csc — Cooja simulation file.
run-nat64-br.sh — Script to start the native border router with NAT64.