RFC 3059

Attribute List Extension for the Service Location Protocol

📅 published February 2001, from ietf

🎀 RFC 3059: Attribute List Extension for the Service Location Protocol ✨

Okay bestie, here's the title block tea 🫶

Network Working Group, Request for Comments 3059. The author is Erik Guttman from Sun Microsystems 💅. It's a Standards Track doc, dated February 2001 🦋. It doesn't obsolete anything, and it doesn't update anything either (no "Obsoletes" or "Updates" listed in the title block) 🌸.

Status of This Memo 📜

No cap, this part is the official boilerplate, so I'm keeping it exactly as written 🤓

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice ©️

   Copyright (C) The Internet Society (2001).  All Rights Reserved.

Abstract 🌟

Okay so SLPv2 (Service Location Protocol, Version 2) is iconic because it can find a service in a single exchange of messages 🦋

The catch is that this exchange doesn't include any of the service's attributes yet 🙈. This doc adds an extension that lets a User Agent (UA) ask for a service's attributes to be included in Service Reply messages. That means no more multiple round trips just to get all the service info. Main character energy, literally 👑

Table of Contents 🗺️

Here's the map of the whole doc, verbatim 💜

   1. Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 2
       1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 2
       1.2. Notation Conventions  . . . . . . . . . . . . . . . . . . 3
   2. Attribute List Extension  . . . . . . . . . . . . . . . . . . . 3
   3. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 4
   4. Internationalization Considerations . . . . . . . . . . . . . . 4
   5. Security Considerations . . . . . . . . . . . . . . . . . . . . 4
   6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 4
   References . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 5
   Full Copyright Statement . . . . . . . . . . . . . . . . . . . . . 6

1. Introduction 🧚

SLPv2 [3] lets a service get discovered in one single exchange of messages 🦋. The UA sends a Service Request message, and then the DA or SA (whichever applies) sends back a Service Reply message 💌.

It's giving "obviously you want all the info at once" 💅. SLP keeps different kinds of info in separate messages, and this extension is an optimization on the basic exchange, since right now Service Reply messages don't carry service attributes 🙃.

So this doc specs a SLPv2 extension that lets a UA ask for a service's attributes to be included in Service Reply messages 💖. It kills the need for multiple round trips just to grab all the service info ✨.

Now the important fine print 👀 If the DA or SA doesn't support the Attrlist extension, it'll just return a Service Reply (no extension) 🫠. Supporting this extension is OPTIONAL 🌈. Existing implementations will ignore the Attrlist extension, because it got an identifying number from the range that tells the receiver it MUST ignore the extension if it doesn't recognize it 🔥. See RFC 2608 [3] for more.

If the UA gets a Service Reply without an Attrlist Extension, it must assume the SA or DA doesn't support the extension 🥺. In that case, the UA must send an Attribute Request for each URL it got in the Service Reply, so it can get the attributes for those services 📨.

1.1. Terminology 📖

User Agent (UA): A process working on the user's behalf to establish contact with some service. The UA retrieves service information from the Service Agents or Directory Agents. 🙋‍♀️
Service Agent (SA): A process working on the behalf of one or more services to advertise the services. 📣
Directory Agent (DA): A process which collects service advertisements. There can only be one DA present per given host. 🗂️

1.2. Notation Conventions ✍️

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 [2]. Those capital words are the ones with real force, so they're kept exactly as the spec has them 🫶

2. Attribute List Extension 🎀

This is the outfit check 👗 Here's the format of the Attribute List Extension:

       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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |      Extension ID = 0x0002    |     Next Extension Offset     |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | Offset, contd.|      Service URL Length       |  Service URL  /
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |     Attribute List Length     |         Attribute List        /
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |# of AttrAuths |(if present) Attribute Authentication Blocks.../
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

The Extension ID is 0x0002 🔢.

The Next Extension Offset value tells you where the next extension starts, counted as an offset from the beginning of the SLP message. If the next extension offset value is 0, there are no more extensions in the message 🏁.

A UA sends an Attribute List Extension with a Service Request 📤. The Service URL Length and Attribute List Length are set to 0, and the Service URL and Attribute List fields are left out in this case. That's how the UA asks the SA or DA to put an Attribute List Extension in its Service Reply: by including an 'empty' Attribute List Extension in the Service Request 🥹.

An SA or DA that supports the Attribute List Extension returns one Attribute List extension for every URL Entry in the Service Reply message 🪄. The order of the Attribute List Extensions SHOULD match the order of the URL Entries in the Service Reply 🧠.

The Service URL [4] identifies the matching URL Entry 🔗.

The Attribute List field is the entire attribute list of the service 📋. These attributes must be in the same language as the one indicated in the Service Request message 🌍.

Heads up, this one's serious 🚨 If the Service Request message includes an SLP SPI string, then the attribute list extension MUST include an authentication block. If the SA or DA doesn't support, or can't return, an authentication block for the SLP SPI included in the Service Request, then the SA or DA MUST NOT return an Attribute List Extension. The authentication block(s) follow exactly the same format as they would in an Attribute Reply or Service Registration message 🔐.

3. IANA Considerations 🏛️

IANA has assigned extension ID number 0x0002 for the Attribute List Extension 🎉.

4. Internationalization Considerations 🌏

The Service Location Protocol, version 2 has mechanisms for allowing attributes to be sent with explicit language tagging [6]. The same mechanisms are used for this protocol extension 🗣️.

5. Security Considerations 🛡️

Okay this section is giving main character, so listen up 🌈👑

The Service Location Protocol, version 2 has mechanisms for returning authenticators along with attribute lists, so that UAs can verify a digital signature over the attributes they get 🔏. This same mechanism is used for this protocol extension. The Attribute List Extension used together with SLPv2 is no less secure than SLPv2 without the extension 💜.

6. Acknowledgments 🫶

The author benefited from early conversations about this extension with Charlie Perkins 💬.

References 📚

Every citation, verbatim 🤓

   [1] Bradner, S., "The Internet Standards Process -- Revision 3", BCP
       9, RFC 2026, October 1996.

   [2] Bradner, S., "Key Words for Use in RFCs to Indicate Requirement
       Levels", BCP 14, RFC 2119, March 1997.

   [3] Guttman, E., Perkins, C., Veizades, J. and M. Day, "Service
       Location Protocol, Version 2", RFC 2608, June 1999.

   [4] Guttman, E., Perkins, C. and J. Kempf, "Service Templates and
       service: Schemes", RFC 2609, June 1999.

   [5] Narten, T and H. Alvestrand, "Guidelines for Writing an IANA
       Considerations Section in RFCs", BCP 26, RFC 2434, October 1998.

   [6] Alvestrand, H., "Tags for the Identification of Languages", BCP
       47, RFC 3066, January 2001.

Author's Address 📮

   Erik Guttman
   Sun Microsystems
   Eichhoelzelstr. 7
   74915 Waibstadt
   Germany

   Phone:    +49 6227 356 202
   EMail:    Erik.Guttman@sun.com

Full Copyright Statement ⚖️

Legal bits, kept complete 💖

   Copyright (C) The Internet Society (2001).  All Rights Reserved.

   This document and translations of it may be copied and furnished to
   others, and derivative works that comment on or otherwise explain it
   or assist in its implementation may be prepared, copied, published
   and distributed, in whole or in part, without restriction of any
   kind, provided that the above copyright notice and this paragraph are
   included on all such copies and derivative works.  However, this
   document itself may not be modified in any way, such as by removing
   the copyright notice or references to the Internet Society or other
   Internet organizations, except as needed for the purpose of
   developing Internet standards in which case the procedures for
   copyrights defined in the Internet Standards process must be
   followed, or as required to translate it into languages other than
   English.

   The limited permissions granted above are perpetual and will not be
   revoked by the Internet Society or its successors or assigns.

   This document and the information contained herein is provided on an
   "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
   TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
   BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
   HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

Acknowledgement 💌

   Funding for the RFC Editor function is currently provided by the
   Internet Society.

That's the whole doc, bestie 💜 Go forth and implement responsibly 🧚✨

📦 where this page comes from

ietf: rfc3059 2001-02
💖 girlified by claude-haiku-5-5 on 2026-10-16: a language model's rewrite of the original, under its terms