iodine

iodine is a tunnel application that transports IPv4 traffic through DNS, using a client and server to create a virtual network interface and route IP packets over DNS queries and replies. It is commonly used in constrained networks where direct internet access is blocked but DNS is still permitted.

Key Features

• Client/server IP-over-DNS tunnel using a TUN/TAP virtual interface
• Works across multiple platforms (Linux, BSDs, macOS, and Windows)
• Supports multiple DNS record types for transport, with autodetection for best throughput
• Automatic probing of fragment/packet sizes to optimize performance
• Challenge-response login and basic peer filtering to reduce unauthorized injection
• Can fall back to raw UDP tunneling when direct UDP to port 53 is possible

Use Cases

• Remote connectivity from restricted networks that only allow DNS traffic
• Creating a temporary backchannel for administration and troubleshooting
• Running a second-layer VPN or SSH-over-tunnel for more secure transport

Limitations and Considerations

• Carries IPv4 payload only; tunneled traffic is not encrypted by default
• Throughput is constrained and often asymmetric, depending on DNS relays and policies
• Client and server typically need matching versions due to protocol compatibility

iodine is a pragmatic tool for establishing connectivity over DNS when other protocols are blocked, offering portability and performance-focused DNS transport choices. For security-sensitive scenarios, it is best used as a transport for an encrypted layer such as VPN or SSH.