AX.25 on Linux/IP over AX.25

Note: This page is a work in progress. It is not yet complete, and it may contain inaccuracies or outdated information.

Main article: AX.25 on Linux

If your goal with AX.25 on Linux is specifically IP over AX.25, the removal of AX.25 from the Linux kernel has narrowed the range of options.

The upstream discussion explicitly points out that IP over AX.25 can, in principle, be handled from user space, as via TUN/TAP integration, rather than by requiring the historic kernel implementation.

That does not mean there is one complete drop-in replacement ready for every old Linux AX.25 workflow today. It does suggest a long-term architectural direction:

• AX.25 framing and control in user space
• Integration with IP through TUN/TAP or similar interfaces
• Narrower, more maintainable components rather than a large in-kernel subsystem

For now, end users may need to stay on an older kernel until a user-space solution emerges. Interested developers might look into this as an area for contributions to new or existing projects.

One current project that might be relevant for IP over amateur radio projects is tncattach, a separate user-space tool that creates a Linux network interface from a KISS-compatible TNC without relying on the old kernel AX.25 stack.

It is not a user-space replacement for the old Linux AX.25 stack, and it should not be understood as preserving the historic Linux AX.25 interface model. It is aimed instead at IP or Ethernet-style networking over a TNC. If your main use of kissattach was simply to turn a KISS TNC into a Linux network device for IP networking, then tncattach may be worth a look.

It may also be a useful reference point for future development. Even if it does not solve every AX.25-specific use case by itself, it shows one way to bridge a KISS-compatible TNC to a Linux network device without the old kernel stack, and that approach could potentially be extended further or incorporated into other projects.