Subject: Thinking about advancing SLPv2 to draft standard

From: Erik Guttman <[email-masked]>
Date: Thu, 18 May 2000 08:27:46 +0200 (MET DST)

Hello all.  

The time has come to consider moving SLPv2 to draft standard.  

There have been many concerns that 'SLP is too big.'  SLP could well be
trimmed.  The attached draft aims at deprecating all features which I
believe are non-essential and which have not achieved a level of inter-
operability.  The draft includes an analysis of what made SLPv2 complex
to implement and shows how the deprecations remove these features.

Please review the draft and lets discuss if we can add more features
to the list.  If any of the features I suggest are indeed essential,
we can remove them from the list of features to drop.

The goal is that existing SLPv2 agents would not have to be modified,
though UAs might get back some 'not implemented' errors if they use
some of the deprecated features in the future.

The highest goal has to be making SLPv2 stable, lightweight, interoperable
and as broadly useful as possible.

This is only the beginning of the process of advancing SLPv2 to draft
standard.  We need to have a specification which has binary compatibility
with RFC 2608 and for which we get at least interoperable implementations 
of each feature.  Lets think hard about what we really need to keep.

Erik

ps. The draft will be appearing in the i-d directories soon.

Internet Engineering Task Force                            Erik Guttman
INTERNET DRAFT                                              James Kempf
19 May 2000                                            Sun Microsystems
Expires in six months

                     Proposed Modifications to the
                  Service Location Protocol, Version 2
                 <draft-guttman-svrloc-slpv2bis-00.txt>

Status of this Memo

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC2026.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
   other groups may also distribute working documents as Internet-
   Drafts.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   The list of current Internet-Drafts can be accessed at
   http://www.ietf.org/ietf/1id-abstracts.txt

   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html.

   Copyright (C) The Internet Society (2000).  All Rights Reserved.

Abstract

   SLPv2 [1] has been widely implemented but not all features of the
   protocol are in common use.   If these features were deprecated from
   the specification the protocol would be simpler, yet still perform
   its core function.  The changes proposed in this document could be
   the basis for a revision of SLPv2 as it is considered for advancement
   to Draft Standard.

1. Introduction

   SLPv2 has been widely implemented but not all features of the
   protocol are in common use.   If these features were deprecated from
   the specification the protocol would be simpler, yet still perform it
   core features.  The changes proposed in this document could be the
   basis for a revision of SLPv2 as it is considered for advancement to

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   Draft Standard.

   This document begins with the motivation for revision.  Specific
   revisions are proposed.  Finally, minimal requirements for SLPv2bis
   compliant hosts are summarized.

   Changes proposed in this document will not modify any of the SLPv2
   on-the-wire protocol.  Features will be dropped and in a couple cases
   slightly new interpretations of rules are given.

   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].

2.0 Motivation

   There are four features which made SLPv2 complicated to implement.

      - SAs and DAs MUST implement full LDAPv3 search filters [3] for
      matching service requests.  This required complex parsing and
      indexing.  See Section 3.1.

     - Attribute Requests by service type was difficult to collate.  See
      Section 3.2.

     - SAs MUST keep track of all DAs it discovers and forward SrvReg
      and SrvDereg messages to each of them.  This requires the SA to
      passively discover DAs and to maintain and act on non-trivial
      state information.  See Section 3.3.

     - Previous Responder Lists made message headers variable length for
      each retransmission.  See Section 3.4.

   Each of these features has proven to be unnecessary.  In fact many
   implementations have foregone them.

   There are other features which were viewed as useful during the
   design phase of SLPv1 which have not proven their worth in deployment
   and have burdened the protocol unnecessarily.

3.0 Recommended Modifications of SLPv2

   The following section details all suggested changes to the protocol.

3.1 Service Request

     3.1.1. Limit requests to at most 1 '&' logical operator.  Thus,
      only requests of type (x=4) or (&(x=4)(y=3)) are allowed.

     3.1.2. Allow only '=' based comparisons.  Thus all comparisons are

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      case insensitive string based.

     3.1.3. Eliminate support for wild cards in queries.

   The result of these rules will be that SLPv2 search filters will be
   compatible with LDAPv3 search filter, but not visa versa.

   Complicated logical queries for services have not proven useful.
   Allowing conjunctions of required attributes has proven very useful
   and is easy to implement.

   It might be argued that eliminating support for '<=' and '>=' filters
   will make it impossible to do load balancing with SLPv2.  It is
   possible to do load balancing by requesting all services and then
   comparing their attributes for a given value at the UA.  It would
   also be possible to create a SLPv2 extension for load balancing on a
   particular attribute.

3.2 Attribute Request

     3.2.1. Eliminate attribute requests by type.  Attribute requests
      will be by service URL only.

     3.2.2. Eliminate wild cards in attribute request search filters.

   Another possibility would be more radical:

     3.2.3. Deprecate attribute requests entirely as the Attribute List
      Extension [8] may be used when a UA wants to retrieve attributes.

   Attribute requests for service by type have proven difficult to
   implement and interpret.  This feature should be deprecated.

3.3 DA Discovery

     3.3.1. Recommend that DAs do mesh enhancement [7].

   Mesh enhanced DAs add very little complexity to DAs.  If even one is
   present in a given scope, a SA does not need to keep track of other
   DAs in that scope.  Forwarding to the mesh enhanced DA will
   effectively cause a registration to be forwarded to all DAs in that
   scope.

3.4 Transport

     3.4.1. Deprecate Previous Responder lists - but random delays on
      replies are a MUST.  If PR lists are in requests, SAs and DAs MAY
      ignore them.

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   PR lists only work with <100 responders.  In that case, as long as
   replies are staggered there is no overflow risk.  So PR lists are
   really not useful except to suppress responses to save network
   usage).

3.5 Scope Configuration

     3.5.1. Deprecate MANDATORY flags in RFC 2610.

     3.5.2. Use nested scopes in MADCAP [5] for scope config.  SAs and
      DAs join all groups at the top of each nested scope (address
      range).  They advertise all scopes by the name received in the
      MADCAP Nested Scope Option [6].

     3.5.3. The simplified scope configuration list would be in
      decreasing order of preference
             Pref   Feature                           Requirement 'mode'
              1)    static configuration of scope list  MUST
              2)    static configuration of DAs*        MUST
              3)    dhcp configuration                  SHOULD
              4)    dhcp configuration of DAs*          SHOULD
              5)    MADCAP / scope configuration        SHOULD
              6)    dynamic discovery (DAAdverts)**     MAY
              7)    dynamic discovery (SAAdverts)**     MAY
              8)    Use of the scope "default"          MUST

   The higher item on the list always takes precedence over the lower
   items.  If no other configuration is supplied, a SLP Agent is
   configured with the scope list "default".

   * If a scope list is not configured (by through static configuration
     or DHCP) but a list of DAs is, the SLP Agent MUST unicast a
     SrvRqst for "service:directory-agent" to each of the DAs on the
     list.  The SLP Agent is configured with the scope list which is the
     union of all scopes supported by the DAs which respond with a DAAdvert.
     If a DA on the configuration list does not respond, the SLP Agent
     SHOULD try to send it a SrvRqst again periodically (like every 30
     minutes).  Once a DAAdvert is received, the scope list MAY be
     expanded and the # of DAs known of by the SLP Agent increases.

   **Dynamic discovery of scopes MAY be used by User Agents and
     MUST NOT be used to configure Service Agent or Directory Agent
     scope lists.

   The problem with the current scope rules is that they are overly
   complicated.  This is largely due to the 'MANDATORY' bit in the
   SLPv2 DHCP Option [9].  A clarification of how to do scope rules
   using the current specifications shows just how hard it is [10].

   Further, when SLPv2 was published, the Administrative Scoping BCP

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   [4] was available, but further specifications were not.  Now, with
   MADCAP and the MADCAP Nested Scope Option it is possible to define
   specific automatic scope configuration behavior.

3.6 Service Deregistration

     3.6.1. Eliminate wild cards in the tag list for selective attribute
      deregistration.

3.7 String Matching

     3.7.1. Eliminate the requirement to elide white space in
      requests.  If white space is included unintentionally
      on registration or requests - that is an error.  Use
      the templates literally (just don't add unwanted space).
      This effects every message - scope lists, tag lists,
      attribute lists, queries, and so on.

   Eliding white space allowed requests to be 'sloppy' and still
   match strings in registered by other servers.  In practice this
   does not seem to be a problem since strings can be trimmed before
   being registered or before requests are sent.  Many strings are
   will have extra white space due to manual entry anyway.

4.0 Minimal Features

   The following minimal features will result from this trimming
   of SLPv2.

4.1 Directory Agent

     - Send DAAdverts periodically
     - Respond to service requests for DA with DAAdvert
     - Respond to SrvRqst, AttrRqst and SrvTypeRqst with
      SrvRply, AttrRply and SrvTypeRqst
     - Accept SrvReg and SrvDereg messages
     - Age services out of the cache when their lifetimes expire

   The following mandatory features for DAs would be dropped
   due to the proposed revision.

     - Handling Previous Responder Lists.
     - Handling Attribute Requests by service type.
     - Handling wild cards in Service Deregistration tag lists.

   For backward compatibility with existing SLPv2 UAs and SAs
   other features could not be dropped.  However, very few SLPv2
   DAs have been deployed.  It is conceivable that further features

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   (described in section 3) could be made optional for DAs.

4.2 Service Agent

       - Active DA discovery (1)
       - Passive DA discovery (1)
       - Respond to service request for SA with SAAdvert
       - Respond to service requests for services with SrvRply (2)
       - De/Register with discovered DAs (1)

   (1) If mesh enhanced DAs have been discovered, only one DA need be
       registered with.  Further passive DA discovery would not be
       needed once such a DA has been discovered, too.

   (2) SAs return a 'not implemented error' if they cannot parse a
       LDAPv3 search filter.  Clients can then infer that the SA
       can only handle the restricted subset. (Since SLPv2 SAs MUST
       support SrvRqst - the not implemented refers to the search
       filter not to the function).

   The following mandatory features for SAs would be dropped
   due to the proposed revision.

     - Handling Previous Responder Lists.
     - Eliding White Space
     - Handling LDAPv3 search filters
     - Handling wild cards in strings

4.3 User Agent

     - Active DA discovery (1)
     - Multicast SrvRqst if no discovered DAs
     - Unicast SrvRqst if discovered DAs

   (1) Active DA discovery should be done periodically if no DAs
       discovered initially.

   The following mandatory features for UAs would be dropped
   due to the proposed revision.

     - Handling Previous Responder Lists.

5.0 Backward Compatibility

   SLPv2 may be modified to drop features and remain backwardly
   compatible with the current specification.  Only two things
   need to occur to guarantee this.  First, SLPv2 DAs SHOULD
   remain backwards compatible with RFC 2608 features.  Second,

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   SLPv2 UAs and SAs MUST be prepared to accept NOT IMPLEMENTED
   errors for the features which are being dropped.

   The risk of backward compatibility problems is limited because
   client and server systems (UA and SA pairs) tend to be deployed
   together to form end-to-end systems.  As new UAs and SAs are
   deployed, they will not attempt to use the deprecated features.

6.0 Security Considerations

   The modifications described in this memo would not modify the
   security considerations for SLPv2 [1] except in so far as they
   suggest the use of mesh-enhanced registration.  Those security
   considerations are discussed elsewhere [7].

7.0 Acknowledgments

   Mikael Pahmp (Axis Communications) contributed very helpful
   comments which started the process of thinking about how to
   trim down SLPv2.

8.0 References

  [1] Guttman, E., Perkins, C., Veizades, J., Day, M., "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] Howes, T., "The String Representation of LDAP Search Filters",
      RFC 2254, December 1997.

  [4] Meyer, D., "Administratively Scoped IP Multicast", RFC 2365,
      July 1998.

  [5] Hanna, S., Patel, B., Shah, M., "Multicast Address Dynamic
      Client Allocation Protocol (MADCAP)", RFC 2730, December 1999.

  [6] Kermode, R., "MADCAP Multicast Scope Nesting State Option",
      <draft-ietf-malloc-madcap-nest-opt-04.txt>, April 2000,
      A work in progress.

  [7] Zhao, W., Schulzrinne, H., "Interaction of SLP Directory Agents
      for Reliability and Scalability", <draft-zhao-slp-da-
      interaction-03.txt>, May 2000, A work in progress.

  [8] Guttman, E., "Attribute List Extension for the Service Location
      Protocol", draft-guttman-svrloc-attrlist-ext-02.txt, March 1999,

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      A work in progress.

  [9] Perkins, C., Guttman, E., "DHCP Options for Service Location
      Protocol", RFC 2610 June 1999.

 [10] Kempf, J., Pahmp, M., Holm, R., "SLP Scope and DA Configuration",
      <draft-kempf-scope-rules-03.txt>, December 1999, A work in
      progress.

9.0 Authors' Contact Information

      Erik Guttman
      Network and Security Research Center, Sun Laboratories
      Sun Microsystems, Inc.
      Eichhoelzelstr. 7
      74915 Waibstadt
      Germany

      Phone: +49 172 865 5497
      Fax:   +49 7263 911 701
      Email: [email-masked]

      James Kempf
      Network and Security Research Center, Sun Laboratories
      Sun Microsystems, Inc.
      15 Network Circle
      Menlo Park, CA 94025
      USA

      Phone: +1 650 786 5890
      Fax:   +1 650 786 6445
      Email: [email-masked]

10. Full Copyright Statement

Copyright (C) The Internet Society (2000).  All Rights Reserved.
This document and translations of it may be copied and furnished to
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assist in its implementation may be prepared, copied, published and
distributed, in whole or in part, without restriction of any kind,
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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,
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Standards process must be followed, or as required to translate it into
languages other than English.  The limited permissions granted above are

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perpetual and will not be revoked by the Internet Society or its
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---

From: [email-masked]
Date: Thu, 18 May 2000 13:36:02 -0700

Hi,

	Is there any work that is going on to integrate this with LDAP.  How
	does the interoperate with UPnP (SSDP) ?

	Thanks.

--
Regards,
Ebi
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Hewlett-Packard                          email: [email-masked]
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> ps. The draft will be appearing in the i-d directories soon.

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