Internet Protocol Encapsulation of AX.25 Frames
draft-learmonth-intarea-rfc1226-bis-01
Network Working Group I. Learmonth
Internet-Draft HamBSD
Obsoletes: 1226 (if approved) May 26, 2020
Intended status: Experimental
Expires: November 27, 2020
Internet Protocol Encapsulation of AX.25 Frames
draft-learmonth-intarea-rfc1226-bis-01
Abstract
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.
Note
Comments are solicited and should be addressed to the author(s).
The sources for this draft are at:
https://github.com/irl/draft-rfc1226-bis
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
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time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on November 27, 2020.
Copyright Notice
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
Learmonth Expires November 27, 2020 [Page 1]
Internet-Draft AX.25 over IP May 2020
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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
worldwide.
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",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
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
unaltered.
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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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