RFC 3224
Vendor Extensions for Service Location Protocol, Version 2
Okay bestie, gather round 🎀 this is RFC 3224, Vendor Extensions for Service Location Protocol, Version 2 💖. It came out of the Network Working Group, written by E. Guttman at Sun Microsystems, dated January 2002, and it's on the Standards Track 🔥. It updates RFC 2608, which is "The Service Location Protocol" 🧚. Nothing is listed as obsoleted in the header ✨.
Status of This Memo 📜
This document specifies an Internet standards track protocol for the Internet community, and it asks 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 Internet Society (2002). All Rights Reserved. 💜
Abstract 🦋
This document explains how the features of the Service Location Protocol, Version 2 allow for vendor extensibility safely, with no possibility of collisions 🔥. It introduces a brand new SLPv2 extension, the Vendor Opaque Extension 🎀. Proprietary protocol extensions are not encouraged by IETF standards, but it's important that they don't hinder interoperability of compliant implementations when they happen 💅. This document updates RFC 2608, "The Service Location Protocol." ✨
Table of Contents 🗂️
1.0 Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1 Terminology . . . . . . . . . . . . . . . . . . . . . . 2
2.0 Enterprise Numbers . . . . . . . . . . . . . . . . . . . . . 3
3.0 Naming Authorities . . . . . . . . . . . . . . . . . . . . . 3
4.0 Vendor Defined Attributes . . . . . . . . . . . . . . . . . 4
5.0 Vendor Opaque Extension . . . . . . . . . . . . . . . . . . 5
5.1 Vendor Opaque Extension Format . . . . . . . . . . . . . . 6
5.2 Example: Acme Extension for UA Authentication . . . . . . . 6
6.0 Extensions Requiring IETF Action . . . . . . . . . . . . . . 7
7.0 IANA Considerations . . . . . . . . . . . . . . . . . . . . 7
8.0 Security Considerations . . . . . . . . . . . . . . . . . . 8
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . 8
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 9
Full Copyright Statement . . . . . . . . . . . . . . . . . . . . . 101.0 Introduction 🌸
The Service Location Protocol, Version 2 [1] has a bunch of features that are extensible 🧚. This document spells out exactly which mechanisms can be used for that (Sections 3-5) and which can't (Section 6) 💖. It updates [1] and sets conventions so the protocol extension mechanisms in the SLPv2 specification won't have any possible ambiguous interpretations 👑.
This spec introduces only one new protocol element, the Vendor Opaque Extension 🎀. It lets a vendor extend SLP independently, once that vendor has registered with IANA and got an Enterprise Number ✨. It's super useful for vendor-specific applications 💅.
Vendor extensions to standard protocols come with a cost, though 😭:
- Vendor extensions happen without review from the community. They may not make good engineering sense in the context of the protocol they extend, and the engineers responsible may find that out way too late 💀.
- Vendor extensions rule out interoperation with compliant but non-extended implementations. There's a real danger of incompatibility if different implementations support different feature sets 🙈.
- By extending SLPv2 privately, ubiquitous automatic configuration becomes impossible, and that's the primary benefit of a standard service discovery framework 🫶.
For these reasons, registering service templates with IANA is strongly encouraged! It's easy, and it has proved to be rapid, taking less than 2 weeks in most cases 🔥🏃♀️.
1.1 Terminology 💜
In this document, the key words "MAY", "MUST", "MUST NOT", "optional", "recommended", "SHOULD", and "SHOULD NOT", are to be interpreted as described in [2] ✨.
Service Location Protocol terminology is defined in [1]. IANA registration terminology is defined in [5] 🎀.
2.0 Enterprise Number 🎀
Enterprise Numbers are how IETF protocols tell different vendors apart 🧚. Vendor Extensions to SLPv2 SHOULD use these values so there's zero chance of a name space collision 💖. Each vendor is responsible for making sure that vendor extensions under their own authority don't conflict 💅.
IANA keeps a repository of all 'SMI Network Management Private Enterprise Codes,' whose prefix is iso.org.dod.internet.private.enterprise (1.3.6.1.4.1) 🌈. The number that follows is unique and may be registered through an on-line form [3] 🦋.
The complete, up-to-date list of Enterprise Numbers is maintained by IANA [3] 📜.
3.0 Naming Authorities 🧚
Naming Authorities are defined by SLPv2 [1] as an agency or group that catalogues Service Types and attributes 💅.
A Service Type is a string representing a service that can be discovered by SLPv2 ✨. Attributes may be associated with a particular Service Type that's advertised by SLPv2 🌸.
Service Type strings and service attributes may be registered with IANA by creating a Service Template [4] 🎀. The template is included in an internet draft, and an email message is sent to srvloc-list@iana.org requesting that the template be included in the Service Template registry 💌. In this case, the naming authority for the service type is IANA 👑.
It's also possible for a Vendor to create their own naming authority 🔥. In this case, any service type or attribute may be used, and SLPv2 lets arbitrary naming authorities coexist 🦋. To use an explicit naming authority, a vendor simply uses their Enterprise Number as the naming authority 💖. For example, take this (fictitious) Enterprise Number:
9999 Acme, Inc. Erik Guttman femur@example.comThe Naming Authority string to use would be "9999" 🫶. A service: URL that used this Naming Authority to advertise a Roadrunner Detector service could look like this:
service:roadrunner-detector.9999://example.com:9341Service types defined under a naming authority based on an Enterprise Number are guaranteed not to conflict with other service type strings that mean something entirely different 🙈. The same is true of attributes defined for service types under a naming authority 💯.
To create a safe naming authority with no possibility of name collisions, a vendor SHOULD use their Enterprise Number as a naming authority 🛡️✨.
4.0 Vendor Defined Attributes 💅
SLPv2 [1] suggests that:
Non-standard attribute names SHOULD begin with "x-", because no standard attribute name will ever have those initial characters.
It's possible that two non-standard attributes that both use the "x-" prefix notation will conflict 😬. For that reason, vendors SHOULD use "x-" followed by their Enterprise Number and then a "-" to guarantee that the non-standard attribute name's interpretation isn't ambiguous 🎀.
For example, Acme, Inc.'s Enterprise Number is 9999 🍓. Say the Service Template for NetHive (a fictitious game) was:
------------------------------------------------------------
template-type=NetHive
template-version=1.0
template-description=
The popular NetHive game.
template-url-syntax=
url-path = ; There is no path for a NetHive service URL.
features= string M O
# The list of optional features the NetHive server supports.
secure session, fast mode
current-users= string M
# The list of users currently playing
------------------------------------------------------------Acme's server advertises a feature that isn't on the list of standard features, x-9999-cheat-mode 🙈. Only an Acme client would request this attribute to discover servers, since it isn't standard 🕹️.
5.0 Vendor Opaque Extension 🦋
SLPv2 [1] defines a protocol extensibility mechanism 🧚. SLPv2 Extensions get added at the end of a message and have the following format ✨:
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 | Next Extension Offset |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Offset, contd.| Extension Data /
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+The format of the Extension Data depends on the Extension ID 💖. Refer to [4] for a full description of the different mechanisms available for registering values with IANA 📜.
SLPv2 may be extended in any of three ways 🌈.
(1) Anyone may ask the designated expert for SLP to register a new extension ID with IANA 💌. Send requests to svrloc-list@iana.org.
It's recommended that an internet draft specifying this extension be published, with the intention of publishing the document as an Informational RFC 🎀. That way, others can use the extension too 🫶. This isn't a 'vendor extension,' since this is the preferred way of extending the protocol in a vendor neutral manner 👑. If no specification is published and the extension is only meant for vendor specific use, then the 'Vendor Extension' option below probably makes more sense than assigning an extension ID 🙃.
(2) An experimental extension may be done using the range 0x8000 to 0x8FFF 🧪. There's always a risk, though, that another vendor will use the same ID, since these IDs aren't registered 😬.
(3) A Vendor Extension may be used 🏆. This extension lets a Vendor define their own extensions, which are guaranteed to have a unique interpretation ✨. It is OPTIONAL to implement 💅.
5.2 Example: Acme Extension for UA Authentication ✨
okay so picture this 🎀 Acme Corporation, whose Enterprise Number is 9999, is allowed to define an extension to SLP 💅 In this example, Acme makes one extension to add application level access control to service information 🔐 The vibe is that replies only go to clients who can prove who they are 🫶
The engineers at Acme give the Extension Data this form:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|ACME Ext ID = 1| Client ID Length | Client ID ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Timestamp |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Authenticator ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ACME Ext ID: the ACME engineers decided the first byte of their extension data is an extension ID field 🧚 Later, ACME might decide to define more than this one extension. Since there are 8 bits in the ID field, ACME can define up to 256 different extensions 🤯 If ACME skipped this field and started straight with their 'Extension for UA Authentication', they could only ever define one ACME specific SLP extension 💀 For the 'Extension for UA Authentication,' the ACME Extension ID is set to 1. This ID has to be managed within ACME, so each new extension they invent gets a unique ID 🍓
Client ID Length: this says how many bytes of Client ID data follow 📏
Client ID: the Acme application user ID 🎀
Timestamp: # of seconds since January 1, 2000, 0:00 GMT ⏰
Authenticator: a 16 byte MD5 digest [6] calculated over the following data fields, concatenated together 🔑
- UA request bytes, including the header, but not any extensions.
- UA SECRET PASS PHRASE
- Acme UA Authentication Extension - Client ID
- Acme UA Authentication Extension - Timestamp
okay the SA or DA that gets this extension, and supports it, checks three things 👀 First, does it (1) recognize the Client ID? Second, does it (2) have an associated SECRET PASS PHRASE for that Client ID? Third, (3) when it calculates an MD5 digest over the same data listed above, does it come out to the same Authenticator value that's in the extension? If all 3 of these steps succeed, the UA has been authenticated 🥹✨
ngl, this example is for explanatory purposes only 🙈 It would not work well in practice. It requires a shared secret to be configured in SAs and DAs, for every UA. Furthermore, the UA secret pass phrase would be susceptible to a dictionary attack. 💀
6.0 Extensions Requiring IETF Action 🌈
so anything that changes or extends any feature of SLPv2 whatsoever is a different story, unless it's one of the things covered in Sections 3-5 of this document 📚 Those need a standards action as defined in [1] 🫠
Terminology and procedures for IETF Actions related to registering IDs with IANA are defined in [5]. Existing SLPv2 extension assignments are registered with IANA [3] 🗂️
7.0 IANA Considerations 🦋
this document clarifies procedures described in other documents [1] [4] 💅 The Vendor Opaque Extension ID has already been registered [3]. No additional IANA action is required for publication of this document ✅
8.0 Security Considerations 🔐💀
this part is seriously important, bestie 😭 Vendor extensions may introduce additional security considerations into SLP.
This memo describes mechanisms which are standardized elsewhere [1] [4]. The only protocol mechanism described in this document (see Section 5 above) is no less secure than 'private use' extensions defined in SLPv2 [1] 🔒
The example in Section 5.2 above shows how Vendor Opaque Extensions can be used to include an access control mechanism in SLP, so that SAs can enforce an access control policy using an authentication mechanism. This is merely an example, and protocol details were intentionally not provided. A vendor could, however, create a mechanism similar to this one and provide additional security services to SLPv2 in the manner indicated in the example 🛡️✨
Acknowledgements 🫶
Erik says thank you to the IESG 🙏 for their usual persistence and attention to detail 🌸
References 📚
[1] Guttman, E., Perkins, C., Veizades, J. and M. Day, "Service Location Protocol, Version 2", RFC 2608, July 1999.
[2] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997.
[3] http://www.iana.org/numbers.html
[4] Guttman, E., Perkins, C. and J. Kempf, "Service Templates and URLs", RFC 2609, July 1999.
[5] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA Considerations Section in RFCs", BCP 26, RFC 2434, October 1998.
[6] Rivest, R., "The MD5 Message-Digest Algorithm", RFC 1321, April 1992.
Author's Address 🖊️
Erik Guttman Sun Microsystems Eichhoelzelstr. 7 74915 Waibstadt Germany
Phone: +49 7263 911 701 Messages: +49 6221 356 202 EMail: erik.guttman@sun.com
Full Copyright Statement ©️
Copyright (C) The Internet Society (2002). All Rights Reserved.
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Acknowledgement 💖
Funding for the RFC Editor function is currently provided by the Internet Society. ✨
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