AX.25 over IP: Internet protocol encapsulation of AX.25 frames
A method for carrying AX.25 amateur packet-radio frames inside IP datagrams.
Kantor, B., "Internet protocol encapsulation of AX.25 frames", RFC 1226, DOI 10.17487/RFC1226, May 1991, <https://www.rfc-editor.org/info/rfc1226>.
@misc{rfc1226,
series = {Request for Comments},
number = 1226,
howpublished = {RFC 1226},
publisher = {RFC Editor},
doi = {10.17487/RFC1226},
url = {https://www.rfc-editor.org/info/rfc1226},
author = {B. Kantor},
title = {{Internet protocol encapsulation of AX.25 frames}},
pagetotal = 2,
year = 1991,
month = may,
} RFC text
Contents
Network Working Group B. Kantor
Request for Comments: 1226 Univ. of Calif San Diego
May 1991
Internet Protocol Encapsulation of AX.25 Frames
Status of this Memo
This memo describes a method for the encapsulation of AX.25 (the
Amateur Packet-Radio Link-Layer Protocol) frames within IP packets.
This technique is an Experimental Protocol for the Internet
community. Discussion and suggestions for improvement are requested.
Please refer to the current edition of the "IAB Official Protocol
Standards" for the standardization state and status of this protocol.
Distribution of this memo is unlimited.
The AX.25 Amateur Packet-Radio Link-Layer Protocol
The AX.25 Amateur Packet-Radio Link-Layer Protocol is described in
the publication by that name [1], incorporated here by reference.
Each AX.25 packet ("frame") is encapsulated in one IP datagram.
Normally no AX.25 frame will exceed 330 octets, so fragmentation at
the IP layer should not be necessary. However, experiments with
larger AX.25 frame sizes may require the use of standard IP
fragmentation and reassembly procedures.
When an AX.25 frame is encapsulated within an IP packet, HDLC framing
elements (flags and zero-stuffing) are omitted, as the IP datagram
adequately delimits the beginning and end of each AX.25 frame. The
16-bit CRC-CCITT frame check sequence (normally generated by the HDLC
transmission hardware) is included. In all other respects, AX.25
frames are encapsulated unaltered.
Each such IP datagram shall have a protocol number of 93.
Reference
[1] AX.25 Amateur Packet-Radio Link-Layer Protocol Version 2.0
October 1984. Available from the American Radio Relay League,
Newington CT USA 06111, and other sources.
Security Considerations
Security issues are not discussed in this memo.
Author's Address
Brian Kantor
University of California at San Diego
Network Operations C-024
La Jolla, CA 92093-0214
Phone: (619) 534-6865
EMail: brian@UCSD.EDU
ISO Plain Language
On this page
§1Carrying AX.25 in IP
AX.25 is an Amateur Packet-Radio Link-Layer Protocol. RFC 1226 describes how to encapsulate its frames within IP datagrams.
Each AX.25 frame is placed in one IP datagram, which uses protocol number 93. A typical AX.25 frame normally does not exceed 330 octets, so IP fragmentation should not be necessary in the usual case.
One AX.25 frame goes inside one IP datagram. The IP protocol number identifies the datagram as carrying an AX.25 frame.
§1What the Encapsulation Keeps
When an AX.25 frame is put in an IP datagram, the HDLC framing elements (flags and zero-stuffing) are omitted. The IP datagram marks the start and end of the encapsulated frame.
The 16-bit CRC-CCITT frame check sequence is included. In all other respects, the AX.25 frame is encapsulated unaltered. Larger experimental frame sizes may require standard IP fragmentation and reassembly.
IP supplies the outer boundary, so the HDLC flags and zero-stuffing are left out. The frame's 16-bit check sequence remains inside.
§1Protocol Number and Scope
Every IP datagram that carries an AX.25 frame uses protocol number 93. The RFC refers readers to the AX.25 Amateur Packet-Radio Link-Layer Protocol Version 2.0 for the frame format itself.
The document says that security issues are not discussed.
Protocol number 93 identifies IP datagrams containing AX.25 frames. The AX.25 reference document defines the frame protocol.