RFC 4917

RFC 4917 🎀 Mobile IPv4 Message String Extension

Okay bestie, let's talk about RFC 4917 💖 It's the Mobile IPv4 Message String Extension, written by Venkateshwara Sastry (Samsung Electronics) and Kent Leung and Alpesh Patel (both Cisco Systems). It came out in June 2007 from the Network Working Group, and it's on the Standards Track ✨ The header doesn't say it obsoletes or updates any other documents, so it's standing on its own 🦋

Status of This Memo 💌

This document specifies an Internet standards track protocol for the Internet community, and it's asking for discussion and suggestions for improvements 💬 For the standardization state and status of this protocol, check the current edition of the "Internet Official Protocol Standards" (STD 1) 📚 Distribution of this memo is unlimited 🌍

Copyright Notice 💅

Copyright (C) The IETF Trust (2007).

Abstract 🌸

This doc adds a new extension for Mobile IPv4 🧚 The Home Agent and the Foreign Agent can add it to Registration Reply messages, and it carries a text string meant for the user of the Mobile Node 💖

Table of Contents 🧚

1. Introduction ....................................................2
2. Terminology .....................................................2
3. Mobile IPv4 Message String Extension Format .....................2
4. Operation and Use of the Message String Extension ...............3
5. Security Considerations .........................................4
6. IANA Considerations .............................................4
7. Acknowledgements ................................................5
8. Normative References ............................................5

1. Introduction ✨

Okay so this doc adds a brand-new skippable extension that the Foreign Agent and Home Agent can tack onto any registration message aimed at the Mobile Node 💌 That message can be either a Registration Reply or a Registration Revocation (aka co-located Care-of Address mode, iykyk) 🫶 For Registration Reply, the extension can show up whether the registration worked or flopped 😭

What the text string says and how the Mobile Node uses it is totally implementation specific 🙈 It's meant for the user of the Mobile Node, so it could pop up on the user interface, get logged, or be handled some other implementation-dependent way, depending on what kind of Mobile Node it is 📱

Usually the text is a registration failure reason or a welcome message when things go right 🎀 This is a big deal, because the failure reason code gives the user super limited info. So a string like "registration failed : Prepaid Quota for the user is exhausted" gives a human-readable description of the result of the Mobile IP registration. Iconic, honestly 👑

2. Terminology 💜

Quick vocab check 💅 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 RFC 2119 [RFC2119].

3. Mobile IPv4 Message String Extension Format 🦋

The Message String Extension follows the Short Extension format specified for Mobile IPv4 [RFC3344] 🧚 It's a skippable extension too 🌈

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Type      |   Length      |    Sub-Type   |    Text ....
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Let's break down the fields 🍓

Type: 145, an 8-bit identifier of the type mobility option. Main character number! 👑

Length: An 8-bit unsigned integer. This is the length of the extension, in bytes, excluding the extension Type and the extension Length fields. This field MUST be set to 1 plus the total length of the Text field. Non-negotiable 🔥

Sub-Type: Tells you who sent it 👀

• 1: Extension comes from the Home Agent
• 2: Extension comes from the Foreign Agent

Text: The Text field is one or more octets, and its contents are implementation dependent. It's meant to be human readable, and it MUST NOT affect the operation of the protocol 🙅‍♀️ The message MUST be in UTF-8 encoded ISO-10646 [RFC3629] characters. The number of octets in the encoded representation of the message is always exactly the value of the Length field minus one. (The number of unicode characters this octet sequence represents may be smaller than the number of octets, so don't get confused by that 🤓)

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Part 2 picks up right at Section 4 💖

Intellectual Property 🎀

okay so bestie, this part is all about who owns what 💅 The IETF doesn't take a stance on whether any intellectual property rights someone might claim cover the tech in this doc are valid or how far they reach. It also doesn't say it looked into whether any such rights exist 🙈 If you want the rules on rights in RFC documents, check out BCP 78 and BCP 79 ✨

Any IPR disclosures sent to the IETF Secretariat, plus any promises of licenses, or the results of trying to get a general license or permission for implementers or users to use those proprietary rights, can be found in the IETF's online IPR repository at http://www.ietf.org/ipr 🦋

The IETF is basically asking everyone 🫶 If you know about any copyrights, patents, patent applications, or other proprietary rights that might cover tech you'd need to build this standard, please tell them at ietf-ipr@ietf.org 💜

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Acknowledgement 🌸

Shoutout to the people funding the RFC Editor function! Right now, that funding comes from the Internet Society 🍓🧚