Internet Engineering Task Force Erik Guttman INTERNET DRAFT Sun Microsystems 3 July 2000 Expires in six months Service Location Protocol Modifications for IPv6 draft-ietf-svrloc-ipv6-09.txt Status of this Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC 2026 [1]. 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 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. Abstract 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 administration. The Service Location Protocol, Version 2 is well defined for use over IPv4 networks [3]: 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 does not describe how to use SLPv1 [2] over IPv6 networks. There is at the time of this publication no implementation or deployment of SLPv1 over IPv6. It is RECOMMENDED that SLPv2 be used in general, and specifically on networks which support IPv6. Guttman Expires: 3 January 2000 [Page 1] Internet Draft Service Location Modifications for IPv6 July 2000 Table of Contents 1. Protocol Changes . . . . . . . . . . . . . . . . . . . . 2 2. Eliminating support for broadcast SLP requests . . . . . 2 3. Address Specification for IPv6 Addresses in URLs . . . . 3 4. SLP multicast behavior over IPv6 . . . . . . . . . . . . 3 4.1. SLPv2 Multicast Addresses for IPv6 . . . . . . . . . . . 4 4.2. SLPv2 Multicast Scopes for IPv6 . . . . . . . . . . . . 5 5. Restricted Propagation of Service Advertisements . . . . 6 6. IANA Considerations . . . . . . . . . . . . . . . . . . . 8 7. Security Considerations . . . . . . . . . . . . . . . . . 9 Acknowledgments . . . . . . . . . . . . . . . . . . . . . 10 References . . . . . . . . . . . . . . . . . . . . . . . 10 Author's Contact Information . . . . . . . . . . . . . . 11 Full Copyright Statement . . . . . . . . . . . . . . . . 11 1. 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 - Address Specification for IPv6 Addresses in URLs - Use of IPv6 multicast addresses and IPv6 address scopes - Restricted Propagation of Service Advertisements 2. Eliminating support for broadcast SLP requests Service Location over IPv4 allows broadcasts to send Service Location request messages. IPv6 makes use of link-local 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 Guttman Expires: 3 January 2000 [Page 2] Internet Draft Service Location Modifications for IPv6 July 2000 User Agent must multicast the request to the appropriate multicast address. This change modifies the requirements described in Section 6.1 (Use of Ports, UDP and Multicast) of the Service Location Protocol [3]. 3. Address Specification for IPv6 Addresses in URLs Whenever possible the DNS [4] name of the service should be used rather than the numerical representation described in this section. 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 services. The format of a "service:" URL is defined in [5]. This URL is an ``absolute URI'' as defined by [6]. A numerical IPv6 address, such as may be used in a "service:" URL, is specified as in [7]. The textual representation defined for literal IPv6 addresses in [8]: ipv6-addr = "[" num-addr "]" num-addr = ; Text represented IPv6 address syntax is as ; specified in RFC 2373 [8], Section 2.2, Examples: This is a site-local scoped address, as could be used in a SLP DAAdvert message. service:directory-agent://[FEC0::323:A3F9:25ff:fe91:109D] This is a link-local scoped address, as could be used by a SA to advertise its service on a IPv6 network with no routers or DNS service. service:printer:ipp://[FE80::a15A:93ff:fe5D:B098]:8080/path 4. SLP multicast behavior over IPv6 Section 4.1 describes how different multicast addresses are used for transmitting and receiving different SLPv2 messages. Section 4.2 describes which scope these addresses have. Guttman Expires: 3 January 2000 [Page 3] Internet Draft Service Location Modifications for IPv6 July 2000 4.1 SLPv2 Multicast Addresses for IPv6 SLPv2 for IPv4 specifies only one multicast address. The reason only one address was used is that there are only 255 relative assignments available for the Administratively Scoped Addresses [10]. IPv6, on the other hand, has scoped addresses and enough range for a range of static assignments. SLPv2 for IPv6 uses the following multicast address assignments: FF0X:0:0:0:0:0:0:116 SVRLOC [Veizades] FF0X:0:0:0:0:0:0:123 SVRLOC-DA [Veizades] FF0X:0:0:0:0:0:1:1000 Service Location -FF0X:0:0:0:0:0:1:13FF The SVRLOC address is used for the following messages: Service Type Request and Attribute Request messages. The SVRLOC-DA address is used for multicast Service Requests for the "service:directory-agent" service type. DAs send unsolicited DA Advert messages to the SVRLOC-DA multicast address. All other multicast Service Request messages are sent to the appropriate Service Location multicast address. SAs join the groups which correspond to the Service Types of the services they advertise. The address is determined using the algorithm provided in SLPv1. The Service Type string used in the SrvRqst is hashed to a value from 0- 1023. This determines the offset into the FF0X::1:1000-13FF range. The has algorithm is defined as follows: An unsigned 32 bit value V is initialized to 0. Each byte of the Service Type UTF-8 [11] encoded string value is considered consecutively. The current value V is multiplied by 33, then the value of the current string byte is added. Each byte in the Service Type string is processed in this manner. The result is contained in the low order 10 bits of V. For example, the following code implements this algorithm: unsigned long slp_hash(const char *pc, unsigned int len) { unsigned long h = 0; while (len-- != 0) { h *= 33; h += *pc++; } return (0x3FF & h); /* round to a range of 0-1023 */ } Guttman Expires: 3 January 2000 [Page 4] Internet Draft Service Location Modifications for IPv6 July 2000 4.2 SLPv2 Multicast Scopes for IPv6 SLPv2 agents MAY use either the site-local scope or link-local scope for transmission of multicast messages. Site-local scope multicast discovery messages will discover services in the same site (whose addresses are either of site-local or global scope). Link- local scope multicast messages will only discover services whose location is on the same link. SLPv2 SAs and DAs MUST join multicast groups in both of the following scopes: site-local scope (FF05) and link-local (FF02). If an SLP agent does not have a site-local or global scope address, it MUST join only the link-local scoped group. Joining both site-local and link-local scope multicast groups ensures that services advertised by SAs and DAs are discoverable by SLPv2 agents whichever multicast scope they issue their requests in. SLP agents MAY join the SVRLOC-DA group in order to receive DAAdverts which are sent by each DA periodically. The SLPv2 agent MUST join both the site- and link-local scoped SVRLOC-DA multicast group (provided it has been configured with either site-local or global scoped address.) That way the SLP agent can detect a DA whether the DAAdvert is sent using link-local or site-local scope multicast. 5. Restricted Propagation of Service Advertisements Section 4.2 defines which multicast scope to use for issuing requests as well as rules for listening for them. These rules ensure that: A. Hosts with a configured site-local or global scope address which issue requests using the site-local multicast scope will only discover services which are advertised by SAs which are configured with site-local or global scope addresses. These requests may discover services advertised in the local site. B. Hosts which issue link-local multicast requests will do so with a link-local source address. These requests will only discover services advertised on that link. It is possible, unless precautions are taken, that a link-local service location may be obtained on a different link. Further, a host which is multihomed and attached to two different sites, could propagate a service location with a site-local address from one site to the other. These services will not be reachable, so SLPv2 must not allow their discovery. The following rules prevent this possibility: 1. URLs containing literal IPv6 addresses MUST NOT be sent to a Guttman Expires: 3 January 2000 [Page 5] Internet Draft Service Location Modifications for IPv6 July 2000 destination address which has a scope different than the scope of than that of the URL address. This prevents the possibility that a UA with a link-local address will obtain a site-local or global scope address for a service and be unable to use it (since the service may be on another link.) This also prevents the possibility that a UA with a site-local or global scope address will obtain a link-local address for a service for a link other than that to which the UA is attached. 2. SAs and DAs which are multihomed MUST NOT propagate service advertisements beyond their the scope of the advertisement. 2.1 Service Locations (in SrvReg, SrvRply, SAAdvert or DAAdvert messages) whose locations are link-local scoped addresses MUST only be sent to SLP agents located on the same link as the service. Each interface of a multihomed device is potentially on a separate link. It is often difficult to determine whether two interfaces are connected to the same link. For that reason a prudent policy is to not issue SLP messages containing link-local service locations except on the interface where the service is known to reside. 2.2 If a multihomed host is configured with more than one site-local address (in more than one site), special rules apply. Service Locations (in SrvReg, SrvRply, SAAdvert or DAAdvert messages) whose locations are site-local scoped addresses MUST only be sent to SLP agents located in the same site as the service. There are three possible scenarios where such messages could be sent. +----+ +----+ +----+ | SA |--------| UA |--------| DA | +----+ Link 1 +----+ Link 2 +----+ or or Site 1 Site 2 Figure 1: Multihomed UA In Figure 1 the UA is multihomed. The UA can issue a service request on Link 1 and discover a service from the SA. There are two possibilities. (1) The UA issues a request using a link-local source address. The SA replies with a service with a link-local address. (2) The UA issues a request with a site-local (site 1) or global address. The SA responds with a service advertisement containing a site-local (site 1) or global scope address. Guttman Expires: 3 January 2000 [Page 6] Internet Draft Service Location Modifications for IPv6 July 2000 In both cases, the UA will be able to communicate with the service whose location it obtains from the SA. The UA may also issue a request to the DA it discovers on Link 2. If it issues a request to the DA using a link-local address, the DA MUST only return services advertisements whose location is on the same link (link 2). If the UA's request is sent with a source address which is site-local or global scope, the DA may return service advertisements whose locations are in the same site (site 2) or whose addresses are global scope. The UA MUST use active discovery to detect DAs before issuing multicast requests, as per SLPv2 [3]. To discover services on an attached link, in the absence of DAs on the link, the UA issues multicast requests in link-local scope, (from a link-local source address). If the UA is unable to discover any DAs using site-local scoped multicast discovery, it may issue site-local scope multicast requests (with a site-local or global scope source address.) These SLPv2 messages may discover services with site-local or global scope addresses. +----+ +----+ +----+ | UA |--------| SA |--------| DA | +----+ Link 1 +----+ Link 2 +----+ or or Site 1 Site 2 Figure 2: Multihomed SA In Figure 2, the SA is multihomed. The SA may receive a request from the UA on Link 1, Site 1. The SA MUST NOT return a link-local address to the UA which is not in the same link-local scope as the request. The SA MUST NOT return a site-local address to the UA which is not in the same site as the UA, either. For example, the SA MUST NOT return an address for a service which is advertised on link 2, site 2. The SA may receive a DAAdvert on Link 2, site 2. The SA MUST NOT send a service registration to the DA with a link-local address which is not in the same link-local scope as the interface which the DAAdvert arrived on. The SA MUST NOT send a service registration to the DA with a site 1 site-local scope to the DA either. The SA MUST NOT include a link-local address in a SAAdvert message which is for a different link than that where the message is sent. The SA MUST NOT include a site-local address in a SAAdvert message to a site other than where the site-local scope is valid. For example, Guttman Expires: 3 January 2000 [Page 7] Internet Draft Service Location Modifications for IPv6 July 2000 the UA could receive a SAAdvert from the SA containing a URL with a Link 1 link-local address or a site-local scope valid in site 1. The SA MUST use both site-local and link-local scope multicast to solicit DAAdvertisements and detect them actively and passively, unless the SA is only configured with a link-local address. In that case it MUST at least use link-local scope multicast to detect DAs. +----+ +----+ +----+ | UA |--------| DA |--------| SA | +----+ Link 1 +----+ Link 2 +----+ or or Site 1 Site 2 Figure 3: Multihomed DA In Figure 3, the DA is multihomed. The DA MUST keep track of which interface registrations were made on. The DA MUST prevent a registration from the SA which contains a Link 2 link-local address from being discovered by the UA. The DA MUST prevent a registration from the SA with a Site 2 site-local address from being discovered by the UA, also. Care must be taken when issuing DAAdverts. The DA must respond to active DA discovery requests using the same scope as the request. For instance, if the SA issues a SrvRqst message for service type "service:directory" from a link-local source address, the DA MUST respond with a link-local (link 2) source address. The DAAdvert would contain a DA URL with a link 2 link-local address as well. The DA must multicast unsolicited DAAdverts on each interface using link-local source (and DA URL) with link-local scope multicast. If the DA has a site-local or global scoped address, it MUST multicast unsolicited DAAdverts on each interface using site-local scoped multicast, as well. That way all SLP agents on the link and the site will be able to discover the DA. 6. IANA Considerations The following IPv6 multicast address range assignment must be registered with IANA. FF0X::1:1000 - FF0X::1:13FF For SLPv2 service discovery. This document defines how to use SLPv2 for link-local and site-local scope service discovery. Future documents may define how SLPv2 may be used with other multicast scopes. The following address range has already been registered [9]. Guttman Expires: 3 January 2000 [Page 8] Internet Draft Service Location Modifications for IPv6 July 2000 FF05::1:1000 - FF05::1:13FF For site-local service discovery. 7. 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 for issuing and processing Service Location messages whenever an appropriate IPSec Security Association exists. [12] 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. Guttman Expires: 3 January 2000 [Page 9] Internet Draft Service Location Modifications for IPv6 July 2000 Acknowledgments Thanks to Dan Harrington, Jim Wood and Alain Durand, Thomas Narten and Erik Nordmark for their reviews of this document. John Veizades contributed to the original version of this document. The hash function is modified from a code fragment attributed to Chris Torek. References [1] Bradner, S., "The Internet Standards Process -- Version 3", RFC 2026, October 1996. [2] Veizades, J., Guttman, E., Perkins, C., Kaplan, S., "Service Location Protocol", RFC 2165, June 1997 [3] Guttman, E., Perkins, C., Veizades, J., Day, M., "Service Location Protocol, Version 2", RFC 2608, June 1999. [4] Mockapetris, P. V. "Domain names - concepts and facilities", RFC 1034. November 1987. Mockapetris, P. V. "Domain names - implementation and specification", RFC 1035. November 1987. [5] Guttman, E., Perkins, C., Kempf, J., "Service Templates and URLs", RFC 2609, Juny 1999. [6] Berners-Lee, T., Fielding, R., and Masinter, L. "Uniform Resource Identifiers (URI): Generic Syntax", RFC 2396, August 1998. [7] Hinden, R., Carpenter, B., "Format for Literal IPv6 Addresses in URL's", RFC 2732 , December, 1999. [8] Hinden, R., Deering, S., "IP Version 6 Addressing Architecture", RFC 2373, July 1998. [9] Hinden, R., Deering, S., "IPv6 Multicast Address Assignments", RFC 2375, July 1997. [10] Meyer, D., "Administratively Scoped IP Multicast", RFC 2365, July 1998. [11] Yergeau, F., "UTF-8, a transformation format of ISO 10646", RFC 2279, January 1998. [12] Kent, S., Atkinson, R. "Security Architecture for the Internet Protocol", RFC 2401, November 1998. Guttman Expires: 3 January 2000 [Page 10] Internet Draft Service Location Modifications for IPv6 July 2000 Author's Contact Information Erik Guttman Sun Microsystems Eichhoelzelstr. 7 74915 Waibstadt Germany Phone: +49 7263 911701 Email: Erik.Guttman@germany.sun.com Full Copyright Statement Copyright (C) The Internet Society (1999). 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. Guttman Expires: 3 January 2000 [Page 11]