Internet Protocol Encapsulation of AX.25 Frames

Document Type Active Internet-Draft (individual)
Author Iain Learmonth 
Last updated 2020-11-19
Replaces draft-learmonth-rfc1226-bis
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Network Working Group                                       I. Learmonth
Internet-Draft                                                    HamBSD
Obsoletes: 1226 (if approved)                          November 19, 2020
Intended status: Experimental
Expires: May 23, 2021

            Internet Protocol Encapsulation of AX.25 Frames


   This document describes a method for the encapsulation of AX.25 Link
   Access Protocol for Amateur Packet Radio frames within IPv4 and IPv6
   packets.  Obsoletes RFC1226.


   Comments are solicited and should be addressed to the author(s).

   The sources for this draft are at:

Status of This Memo

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   provisions of BCP 78 and BCP 79.

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   This Internet-Draft will expire on May 23, 2021.

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   Copyright (c) 2020 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents

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1.  Introduction

   This document describes a method for the encapsulation of AX.25 Link
   Access Protocol for Amateur Packet Radio [AX.25] frames within IPv4
   and IPv6 packets.  It obsoletes [RFC1226].

   AX.25 is a data link layer protocol originally derived from layer 2
   of the X.25 protocol suite and designed for use by amateur radio
   operators.  It is used extensively by amateur packet radio networks

   In addition to specifying how packets should be encapsulated, it
   gives recommendations for DiffServ codepoint marking of the
   encapsulating headers based on the AX.25 frame content and provides
   security considerations for the use of this encapsulation method.

2.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in [RFC2119].

3.  Internet Protocol Encapsulation

   Each AX.25 frame is encapsulated in one IPv4 or IPv6 datagram using
   protocol number 93 as assigned in the Assigned Internet Protocol
   Numbers registry [protocol-numbers].  For AX.25 version 2.0, the
   maximum frame size expected is 330 bytes and implementations MUST be
   prepared to handle frames of this size.  Higher frame sizes can be
   negotiated by AX.25 version 2.2 and so this is a minimum requirement
   and not a limit.

   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 CRC-16-CCITT frame check sequence (normally generated by
   the HDLC transmission hardware) is included trailing the information
   field.  In all other respects, AX.25 frames are encapsulated

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3.1.  Priority Frames

   In normal operation, the DiffServ codepoint field [RFC2474] in the
   encapsulating IP header SHOULD be set to best effort (BE).  The
   exception to this is "priority frames" as specified for AX.25 version
   2.2, including acknowledgement and digipeat frames, which SHOULD have
   the DiffServ codepoint set to AF21 [RFC2597].  A slot is reserved on
   the radio channel for the transmission of these frames and the use of
   this codepoint will permit the frames to arrive promptly at the
   station for transmission.

   For the avoidance of doubt: on decapsulation the AX.25 frame MUST NOT
   be modified based on the DiffServ codepoint on the received
   encapsulating IP header.  The receiver MUST NOT use the DiffServ
   codepoint to infer anything about the nature of the encapsulated
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