Internet Engineering Task Force                            Erik Guttman
INTERNET DRAFT                                         Sun Microsystems
26 October 1998                                           John Veizades
Expires in six months                                     @Home Network

            Service Location Protocol Modifications for IPv6

Status of this Memo

   This document is an Internet-Draft.  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
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   To learn the current status of any Internet-Draft, please check the
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   The Service Location Protocol provides a scalable framework for the
   discovery and selection of network services.  Using this protocol,
   computers using IP based networks no longer need so much static
   configuration of network services for network based applications.
   This is especially important as computers become more portable, and
   users less tolerant of or less able to fulfill the demands of network

   The Service Location Protocol is well defined for use over IPv4
   networks [SLP]:  This document defines its use over IPv6 networks.
   Since this protocol relies on UDP and TCP, the changes to support its
   use over IPv6 are minor.  This document equally applies to SLP,
   version 2 [SLPv2].

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Internet Draft  Service Location Modifications for IPv6     October 1998

Protocol Changes

   The following are  changes required to have the Service Location
   Protocol work over IPv6.  These changes include:

      - Eliminating support for broadcast SLP requests

      - Restricted Propogation of Link Local Addresses

      - Address Specification for IPv6 Addresses in URLs

      - Different multicast addresses

Eliminating support for broadcast SLP requests

   Service Location over IPv4 allows broadcasts to send Service Location
   request messages.  IPv6 makes use of link layer multicast in place of
   broadcast.  Broadcast only configuration for SLP is not supported
   under IPv6. If a User Agent wishes to make a request to discover
   Directory Agents or make a request of multiple Service Agents, the
   User Agent must multicast the request to the appropriate multicast

   This change modifies the requirements described in Section 4.6 (Use
   of TCP, UDP and Multicast in Service Location) and Section 22
   (Implementation Requirements) of the Service Location Protocol [SLP].

Restricted Propogation of Link Local Addresses

   Link local advertisements MUST NOT be used if the SLP Agent has a
   routable address.  Service advertisements will include routable
   addresses in this case.

   Further, without routable addresses all User Agents (UAs), Service
   Agents (SAs) and Directory Agents (DAs) transmit multicast SLP
   messages with a TTL of 1:  This includes SrvRqst, AttrRqst,
   SrvTypeRqst and unsolicited DAAdvert messages.  This request is
   transmitted using a link local scope multicast address.

   If the SA has no routable address it may send a Service Registration
   to a DA using its Link Local address. This may occur in an
   environment where there is no router available. This address must be
   specified in the Service URL using an IPv6 address specification (see

   A DA or SA MAY return URLs in SrvRply messages which contain link
   local IPv6 addresses to UAs, but only with several restrictions.

   First, the DA or SA must not be multihomed.  SLP DAs and SAs MUST NOT

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Internet Draft  Service Location Modifications for IPv6     October 1998

   respond to SLP messages when they are multihomed and use link local

   Second, the DA or SA must not be configured with a routable address.

   Last, the SA and DA must listen only for link local multicast
   requests.  (The DA will listen for multicast DA discovery requests,
   the SA will listen for various multicast requests.)

   If multihomed agents or routable addresses are desired for SLP with
   IPv6, a router MUST be deployed on the network.

Address Specification for IPv6 Addresses in URLs

   When ever possible the DNS name of the service should be used rather
   than the above representation.

   Service Location allows the use of the protocol without the benefit
   of DNS.  This is relevant when a group of systems is connected to
   build a network without any previous configuration of servers to
   support this network.  When Service Location is used in this manner,
   numerical addresses must be used to identify the location of

   A numerical IPv6 address used in a "service:" URL is specified as

        ipv6-addr  =  v6num "-" 6( [v6num] "-") v6num ".ipv6"
                      ; Text represented IPv6 address syntax is as
                      ; specified in RFC 2373 [AD6], Section 2.2,
                      ; replacing ':' with '-'.
        v6num      =  1*4HEXDIGIT

Security Considerations

   User Agents and Directory Agents may ignore all unauthenticated
   Service Location messages when a valid IPSec association exists.

   Service Agents and Directory Agents must be able to use the IP
   Authentication and IP Encapsulating Security Payload in Service
   Location messages whenever an appropriate IPSec Security Association
   exists. [IPsec]

   SLP allows digital signatures to be produced to allow the
   verification of the contents of messages.  There is nothing
   in the Modifications for IPv6 document which weakens or
   strengthens this technique.

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Internet Draft  Service Location Modifications for IPv6     October 1998

Assigned numbers for IPv6

   The assigned multicast addresses for SLP under IPv4 differ from
   those in IPv6.  These numbers are defined in [MC6].  Their values are:

           FF0X:0:0:0:0:0:0:116     SVRLOC               [Veizades]
           FF0X:0:0:0:0:0:0:123     SVRLOC-DA            [Veizades]
           FF05:0:0:0:0:0:1:1000    Service Location     [RFC2165]

   The SLPv1 General Service Location Multicast address and the Directory
   Agent Discovery Multicast address have been assigned for IPv6, see
   [MC6].  For SLPv2, only the SVRLOC multicast is used (not the SVRLOC-DA
   address.  These addresses are define in [MC6].)

   Note that for SLPv2, multicast TTL is not used to limit the
   propogation of service location multicast requests.  Instead,
   Administratively Scoped multicast addresses [ADM] are used in
   IPv4 and 'site-local scope' multicast [AD6] is used in IPv6.


   Thanks to Dan Harrington, Jim Wood and Alain Durand for their thoughtful
   reviews of previous drafts of this document.


     [DHCP] Droms, R., "Dynamic Host Configuration Protocol", RFC1541,
           October 1993

     [DNS] Mockapetris, P. V. "Domain names - concepts and facilities",
           RFC 1034.  November 1987.

           Mockapetris, P. V. "Domain names - implementation and
           specification", RFC 1035.  November 1987.

     [IPsec] Atkinson, R. "IP Authentication Header",  RFC 1826,
             August 1995.

             Atkinson, R. "IP Encapsulating Security Payload".  RFC 1827,
             August 1995.

             Atkinson, R. "Security Architecture for the Internet
             Protocol", RFC 1825, August 1995.

     [AD6] Hinden, R., Deering, S., "IP Version 6 Addressing
           Architecture", RFC 2373, July 1998.

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Internet Draft  Service Location Modifications for IPv6     October 1998

     [MC6] Hinden, R., Deering, S., "IPv6 Multicast Address Assignments",
           RFC 2375, July 1997.

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

     [SLP] Veizades, J., Guttman, E., Perkins, C., Kaplan, S., "Service
           Location Protocol", RFC 2165, June 1997

     [SLPv2] Guttman, E., Perkins, C., Veizades, J., Day, M., "Service
           Location Protocol, Version 2",
           draft-ietf-svrloc-protocol-v2-10.txt, October 1998.

     [SURL] Guttman, E., Perkins, C., Kempf, J., "Service Templates and
           URLs", draft-ietf-svrloc-service-scheme-12.txt, October 1998,
           A work in progress.

     [URL] Berners-Lee, T., Fielding, R., and Masinter, L. "Uniform
           Resource Identifiers (URI): Generic Syntax", RFC 2396, August

Author Information

         Erik Guttman
         Sun Microsystems
         Bahnstr. 2
         74915 Waibstadt Germany

         Phone:  +49 7263 911701


         John Veizades
         @Home Network
         385 Ravendale Dr.
         Mountain View, CA 94043

         Phone:  +1 415 944 7332
         Fax:    +1 415 944 8500


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