Internet Engineering Task Force Erik Guttman INTERNET DRAFT Charles Perkins 30 July 1998 Sun Microsystems John Veizades @Home Network Michael Day Intel Service Location Protocol, Version 2 draft-ietf-svrloc-protocol-v2-08.txt Status of This Memo This document is a submission by the Service Location Working Group of the Internet Engineering Task Force (IETF). Comments should be submitted to the srvloc@srvloc.org mailing list. Distribution of this memo is unlimited. 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.'' To view the entire list of current Internet-Drafts, please check the ``1id-abstracts.txt'' listing contained in the Internet-Drafts Shadow Directories on ftp.is.co.za (Africa), ftp.nordu.net (Northern Europe), ftp.nis.garr.it (Southern Europe), munnari.oz.au (Pacific Rim), ftp.ietf.org (US East Coast), or ftp.isi.edu (US West Coast). Abstract The Service Location Protocol provides a scalable framework for the discovery and selection of network services. Using this protocol, computers using the Internet need little or no static configuration of network services for network based applications. This is especially important as computers become more portable, and users less tolerant or able to fulfill the demands of network system administration. Guttman,Perkins,Veizades,Day Expires 30 January 1999 [Page i]
Internet Draft Service Location Protocol, Version 2 30 July 1998 Contents Status of This Memo i Abstract i 1. Introduction 1 1.1. Applicability Statement . . . . . . . . . . . . . . . . . 2 1.2. Changes to the Service Location Protocol from v1 to v2 . 2 2. Terminology 3 2.1. Notation Conventions . . . . . . . . . . . . . . . . . . 3 3. Protocol Overview 4 4. URLs used with Service Location 6 4.1. Service: URLs . . . . . . . . . . . . . . . . . . . . . . 6 4.2. Naming Authorities . . . . . . . . . . . . . . . . . . . 7 4.3. URL Entries . . . . . . . . . . . . . . . . . . . . . . . 8 5. Service Attributes 8 6. Required Features 10 6.1. Use of Ports, UDP, and Multicast . . . . . . . . . . . . 11 6.2. Use of TCP . . . . . . . . . . . . . . . . . . . . . . . 12 6.3. Retransmission of SLP messages . . . . . . . . . . . . . 13 6.4. Strings in SLP messages . . . . . . . . . . . . . . . . . 13 7. Errors 14 8. Required SLP Messages 15 8.1. Service Request . . . . . . . . . . . . . . . . . . . . . 16 8.2. Service Reply . . . . . . . . . . . . . . . . . . . . . . 18 8.3. Service Registration . . . . . . . . . . . . . . . . . . 19 8.4. Service Acknowledgment . . . . . . . . . . . . . . . . . 20 8.5. Directory Agent Advertisement . . . . . . . . . . . . . . 20 8.6. Service Agent Advertisement . . . . . . . . . . . . . . . 21 9. Optional Features 23 9.1. Service Location Protocol Extensions . . . . . . . . . . 23 9.2. Authentication Blocks . . . . . . . . . . . . . . . . . . 24 9.2.1. MD5 with RSA in Authentication Blocks . . . . . . 25 9.2.2. DSA with SHA-1 in Authentication Blocks . . . . . 26 9.2.3. Keyed HMAC with MD5 in Authentication Blocks . . 26 9.3. Authentication of a SrvRply . . . . . . . . . . . . . . . 27 9.4. Incremental Service Registration . . . . . . . . . . . . 27 9.5. Tag Lists . . . . . . . . . . . . . . . . . . . . . . . . 28 Guttman,Perkins,Veizades,Day Expires 30 January 1999 [Page ii]
Internet Draft Service Location Protocol, Version 2 30 July 1998 10. Optional SLP Messages 28 10.1. Service Type Request . . . . . . . . . . . . . . . . . . 28 10.2. Service Type Reply . . . . . . . . . . . . . . . . . . . 29 10.3. Attribute Request . . . . . . . . . . . . . . . . . . . . 29 10.4. Attribute Reply . . . . . . . . . . . . . . . . . . . . . 30 10.5. Attribute Request/Reply Examples . . . . . . . . . . . . 31 10.6. Service Deregistration . . . . . . . . . . . . . . . . . 32 11. Scopes 33 11.1. Scope Rules . . . . . . . . . . . . . . . . . . . . . . . 33 11.2. Administrative and User Selectable Scopes . . . . . . . . 34 11.3. Protected Scopes . . . . . . . . . . . . . . . . . . . . 34 12. Directory Agents 35 12.1. Directory Agent Rules . . . . . . . . . . . . . . . . . . 35 12.2. Directory Agent Discovery . . . . . . . . . . . . . . . . 36 12.2.1. Active DA Discovery . . . . . . . . . . . . . . . 36 12.2.2. Passive DA Advertising . . . . . . . . . . . . . 37 12.3. Reliable Unicast to DAs . . . . . . . . . . . . . . . . . 37 12.4. DA Scope Configuration . . . . . . . . . . . . . . . . . 37 12.5. DAs and Authentication Blocks . . . . . . . . . . . . . . 38 13. SLP Protocol Extensions 38 13.1. Required Attribute Missing Option . . . . . . . . . . . . 38 13.2. Cryptographic Request Option . . . . . . . . . . . . . . 39 14. Protocol Timing Defaults 40 15. Optional Configuration 40 16. IANA Considerations 41 17. Internationalization Considerations 42 18. Security Considerations 43 19. Acknowledgments 43 20. Full Copyright Statement 44 1. Introduction The Service Location Protocol (SLP) provides a flexible and scalable framework for providing hosts with access to information about the existence, location, and configuration of networked services. Traditionally, users have had to find services by knowing the name of a network host (a human readable text string) which is an alias for a network address. SLP eliminates the need for a user to know the name Guttman,Perkins,Veizades,Day Expires 30 January 1999 [Page 1]
Internet Draft Service Location Protocol, Version 2 30 July 1998 of a network host supporting a service. Rather, the user supplies the desired type of service and a set of attributes which describe the service. Based on that description, the Service Location Protocol resolves the network address of the service for the user. SLP provides a dynamic configuration mechanism for applications in local area networks. Applications are modeled as clients that need to find servers attached to any of the available networks within an enterprise. For cases where there are many different clients and/or services available, the protocol is adapted to make use of nearby Directory Agents that offer a centralized repository for advertised services. This document specifies the Service Location Protocol (SLP) in two main parts. The first describes the required features of the protocol. The second describes the extended features of the protocol which are optional, and allow greater scalability. 1.1. Applicability Statement SLP is intended to function within networks under cooperative administrative control. Such networks permit a policy to be implemented regarding security, multicast routing and organization of services and clients into groups which are not be feasible on the scale of the Internet as a whole. SLP has been designed to serve enterprise networks with shared services, and it may not necessarily scale for wide-area service discovery throughout the global Internet, or in networks where there are hundreds of thousands of clients or tens of thousands of services. 1.2. Changes to the Service Location Protocol from v1 to v2 SLP version 2 (SLPv2) corrects race conditions present in SLPv1. In addition, authentication has been reworked to provide more flexibility and protection (especially for DA Advertisements). SLPv2 also changes the formats and definition of many flags and values and reduced the number of 'required features.' SLPv2 clarifies and changes the use of 'Scopes', eliminating support for 'unscoped directory agents' and 'unscoped requests'. Other changes (such as Language and Character set handling) adopt practices recommended by the Internet Engineering Steering Group. Effort has been made to make SLPv2 operate the same whether DAs are present or not. For this reason, a new message (the SAAdvert) has been added. This allows UAs to discover scope information in Guttman,Perkins,Veizades,Day Expires 30 January 1999 [Page 2]
Internet Draft Service Location Protocol, Version 2 30 July 1998 the absence of administrative configuration and DAs. This was not possible in SLPv1. SLPv2 is incompatible in some respects with SLPv1. If a DA supports both SLPv1 and SLPv2 with the same scope, services advertised by SAs using either version of the protocol will be available to both SLPv1 and SLPv2 UAs. 2. 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. Service Type Each type of service has a unique Service Type string. Naming Authority The agency or group which catalogues given Service Types and Attributes. The default Naming Authority is IANA. Scope A set of services, typically making up a logical administrative group. URL A Universal Resource Locator [9]. SLPv1 The version of SLP specified in RFC 2165 [24]. 2.1. 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 [10]. Syntax Syntax for string based protocols follow the conventions defined for ABNF [13]. Guttman,Perkins,Veizades,Day Expires 30 January 1999 [Page 3]
Internet Draft Service Location Protocol, Version 2 30 July 1998 Strings All strings are encoded using the UTF8 [25] transformation of the Unicode [6] character set and are NOT null terminated when transmitted. Strings are preceded by a two byte length field. <string-list> A comma delimited list of strings with the following syntax: string-list = string / string `,' string-list In format diagrams, any field ending with a \ indicates a variable length field, given by a prior length field in the protocol. 3. Protocol Overview The Service Location Protocol supports a framework by which client applications are modeled as 'User Agents' and services are advertised by 'Service Agents.' A third entity, called a 'Directory Agent' provides scalability to the protocol. The User Agent issues a 'Service Request' (SrvRqst) on behalf of the client application, specifying the characteristics of the service which the client requires. The User Agent will receive a Service Reply (SrvRply) specifying the location of all services in the network which satisfy the request. The Service Location Protocol framework allows the User Agent to directly issue requests to Service Agents. In this case the request is multicast. Service Agents receiving a request for a service which they advertise unicast a reply containing the service's location. +------------+ ----Multicast SrvRqst----> +---------------+ | User Agent | | Service Agent | +------------+ <----Unicast SrvRply------ +---------------+ In larger networks, one or more Directory Agents are used. The Directory Agent functions as a cache. Service Agents send register messages (SrvReg) containing all the services they advertise to Directory Agents and receive acknowledgements in reply (SrvAck). These advertisements must be refreshed with the Directory Agent or they expire. User Agents unicast requests to Directory Agents instead of Service Agents if any Directory Agents are known. +-------+ -Unicast SrvRqst-> +-----------+ <-Unicast SrvReg- +--------+ | User | | Directory | |Service | | Agent | | Agent | | Agent | +-------+ <-Unicast SrvRply- +-----------+ -Unicast SrvAck-> +--------+ Guttman,Perkins,Veizades,Day Expires 30 January 1999 [Page 4]
Internet Draft Service Location Protocol, Version 2 30 July 1998 User and Service Agents discover Directory Agents two ways. First, they issue a multicast Service Request for the 'Directory Agent' service when they start up. Second, the Directory Agent sends an unsolicited advertisement infrequently, which the User and Service Agents listen for. In either case the Agents receive a DA Advertisement (DAAdvert). +---------------+ --Multicast SrvRqst-> +-----------+ | User or | <--Unicast DAAdvert-- | Directory | | Service Agent | | Agent | +---------------+ <-Multicast DAAdvert- +-----------+ Services are grouped together using 'scopes'. These are strings which identify services which are administratively identified. A scope could indicate a location, administrative grouping, proximity in a network topology or some other category. Service Agents and Directory Agents are always assigned a scope string. A User Agent is normally assigned a scope string (in which case the User Agent will only be able to discover that particular grouping of services). This allows a network administrator to 'provision' services to users. Alternatively, the User Agent may be configured with no scope at all. In that case, it will discover all available scopes and allow the client application to issue requests for any service available on the network. +---------+ Multicast +-----------+ Unicast +-----------+ | Service | <--SrvRqst-- | User | --SrvRqst-> | Directory | | Agent | | Agent | | Agent | | Scope=X | Unicast | Scope=X,Y | Unicast | Scope=Y | +---------+ --SrvRply--> +-----------+ <-SrvRply-- +-----------+ In the above illustration, the User Agent is configured with scopes X and Y. If a service is sought in scope X, the request is multicast. If it is sought in scope Y, the request is unicast to the DA. Finally, if the request is to be made in both scopes, the request must be both unicast and multicast. Scopes for which the User, Service or Directory Agent is configured with cryptographic keying material are called 'protected scopes'. These allow Service Agents to digitally sign their advertisements. User and Directory Agents verify this signature before accepting advertisements in protected scopes. The features described up to this point are required to implement. A minimum implementation consists of a User Agent, Service Agent or both. There are several optional features in the protocol. Guttman,Perkins,Veizades,Day Expires 30 January 1999 [Page 5]
Internet Draft Service Location Protocol, Version 2 30 July 1998 Service Type Request A request for all types of service on the network. This allows generic service browsers to be built. Service Type Reply A reply to a Service Type Request. Attribute Request A request for attributes of a given type of service or attributes of a given service. Attribute Reply A reply to an Attribute Request. Service Deregister A request to deregister a service or some attributes of a service. Service Update A subsequent SrvRqst to an advertisement. This allows individual dynamic attributes to be updated. SA Advertisement In the absense of Directory Agents, a User agent may request Service Agents in order to discover their scope configuration. The User Agent may use these scopes in requests. In the absense of Multicast support, Broadcast may be used. The location of DAs may be staticly configured, discovered using SLP as described above, or configured using DHCP. If a message is too large, it may be unicast using TCP. A SLPv2 implementation MAY support SLPv1 [24]. 4. URLs used with Service Location A Service URL indicates the location of a service. This URL may be of the service: scheme [15] (reviewed in section 4.1), or any other URL scheme conforming to the URL standard [9], except that URLs without address specifications SHOULD NOT be advertised by SLP. The service type for an arbitrary URL is typically its scheme name. For example, the service type string for "http://www.srvloc.org" would be "http". Reserved characters in URLs follow the rules in [9]. 4.1. Service: URLs Service URL syntax and semantics are defined in [15]. Any network service may be encoded in a Service URL. Guttman,Perkins,Veizades,Day Expires 30 January 1999 [Page 6]
Internet Draft Service Location Protocol, Version 2 30 July 1998 This section provides an introduction to Service URLs and an example showing a simple application of them, representing standard network services. A Service URL may be of the form: "service:"<srvtype>"://"<addrspec> The Service Type of this service: URL is defined to be the string up to (but not including) the final `:' before <addrspec>, the address specification. <addrspec> is a hostname (which should be used if possible) or dotted decimal notation for a hostname, followed by an optional `:' and port number. A service: scheme URL may be formed with any standard protocol name by concatenating "service:" and the reserved port [1] name. For example, "service:tftp://myhost" would indicate a tftp service. An http service on a nonstandard port could be "service:http://webby:8080". Service Types SHOULD be defined by a "service template" [15], which provides expected attributes, values and protocol behavior. An abstract service type (also described in [15]) has the form "service:<abstract-type>:<concrete-type>". The service type string "service:<abstract-type>" matches all services of that abstract type. If the concrete type is included also, only these services match the request. For example: a SrvRqst or AttrRqst which specifies "service:printer" as the Service Type will match the URL service:printer:lpr://hostname and service:printer:http://hostname. If the requests specified "service:printer:http" they would match only the latter URL. An optional substring MAY follow the last `.' character in the <srvtype> (or <abstract-type> in the case of an abstract service type URL). This substring is the Naming Authority, as described in Section 9.6. Service types with different Naming Authorities are quite distinct. In other words, service:x.one and service:x.two are different service types, as are service:abstract.one:y and service:abstract.two:y. 4.2. Naming Authorities A Naming Authority MAY optionally be included as part of the Service Type string. The Naming Authority of a service defines the meaning Guttman,Perkins,Veizades,Day Expires 30 January 1999 [Page 7]
Internet Draft Service Location Protocol, Version 2 30 July 1998 of the Service Types and attributes registered with and provided by Service Location. The Naming Authority itself is typically a string which uniquely identifies an organization. IANA is the implied Naming Authority when no string is appended. "IANA" itself MUST NOT be included explicitly. Naming Authorities may define Service Types which are experimental, proprietary or for private use. Using a Naming Authority, one may either simply ignore attributes upon registration or create a local-use only set of attributes for one's site. The procedure to use is to create a 'unique' Naming Authority string and then specify the Standard Attribute Definitions as described above. This Naming Authority will accompany registration and queries, as described in Sections 8.1 and 8.3. Service Types SHOULD be registered with IANA to allow for Internet-wide interoperability. 4.3. URL Entries 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Reserved | Lifetime | URL Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |URL len, contd.| URL (variable length) \ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |# of URL auths | Auth. blocks (if any) \ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ SLP stores URLs in protocol elements called URL Entries, which associate a length, a lifetime, and possibly authentication information along with the URL. URL Entries, defined as shown above, are used in Service Replies and Service Registrations. 5. Service Attributes A service advertisement is often accompanied by Service Attributes. These attributes are used by UAs in Service Requests to select appropriate services. The allowable attributes which may be used are typically specified by a Service Template [15] for a particular service type. Services which are advertised according to a standard template MUST register all service attributes which the standard template requires. URLs with schemes other than "service:" MAY be registered with attributes. Non-standard attribute names SHOULD begin with "x-", because no standard attribute name will ever have those initial characters. Guttman,Perkins,Veizades,Day Expires 30 January 1999 [Page 8]
Internet Draft Service Location Protocol, Version 2 30 July 1998 An attribute list is a string encoding of the attributes of a service. The following ABNF [13] grammar defines attribute lists: attr-list = attribute / attribute `,' attr-list attribute = `(' attr-tag `=' attr-val-list `)' / attr-tag attr-val-list = attr-val / attr-val `,' attr-val-list attr-tag = 1*safe-tag attr-val = intval / strval / boolval / opaque intval = [-]1*DIGIT strval = 1*safe-val boolval = "true" / "false" opaque = "\FF" 1*escape-val safe-val = ; Any character except reserved. safe-tag = ; Any character except reserved, star and bad-tag. reserved = `(' / `)' / `,' / `\' / `!' / `<' / `=' / `>' / `~' / CTL escape-val = `\' HEXDIGIT HEXDIGIT bad-tag = CR / LF / HT / `_' star =`*' The <attr-list>, if present, MUST be scanned prior to evaluation for all occurrences of the escape character `\'. Reserved characters MUST be escaped (other characters MUST NOT be escaped). All escaped characters must be restored to their value before attempting string matching. For Opaque values, escaped characters are not converted - they are interpreted as bytes. Boolean Strings which have the form "true" or "false" can only take one value and may only be compared with '='. Booleans are case insensitive when compared. Integer Strings which take the form [-] 1*<digit> and fall in the range "-2147483648" to "2147483647" are considered to be Integers. These are compared using integer comparison. String All other Strings are matched using strict lexical ordering (see Section 6.4). Opaque Opaque values are sequences of bytes. These are distinguished from Strings since they begin with the sequence "\FF". This, unescaped, is an illegal UTF8 encoding, indicating that what follows is a sequence of bytes expressed in escape notation which constitute the binary value. For example, a '0' byte is encoded "\FF\00". A string which contains escaped values other than from the reserved set of characters is illegal. If such a string is included in an Guttman,Perkins,Veizades,Day Expires 30 January 1999 [Page 9]
Internet Draft Service Location Protocol, Version 2 30 July 1998 <attr-list>, <tag-list> or search filter, the SA or DA which receives it MUST return a PARSE_ERROR to the message. A keyword has only an <attr-tag>, and no values. Attributes can have one or multiple values. All values are expressed as strings. When values have been advertised by a SA or are registered in a DA, they can take on implicit typing rules for matching incoming requests. Stored values must be consistent, i.e., x=4,true,sue,\ff\00\00 is disallowed. A DA or SA receiving such an <attr-list> MUST return an INVALID_REGISTRATION error. 6. Required Features This section defines the minimal implementation requirements for SAs and UAs as well as their interaction with DAs. A DA is not required for SLP to function, but if it is present, the UA and SA MUST interact with it as defined below. A minimal implementation may consist of either a UA or SA or both. The only required features of a UA are that it can issue SrvRqsts according to the rules below and interpret DAAdverts, SAAdverts and SrvRply messages. The UA MUST issue requests to DAs as they are discovered. An SA MUST reply to appropriate SrvRqsts with SrvRply or SAAdvert messages. The SA MUST also register with DAs as they are discovered. UAs perform discovery by issuing Service Request messages. SrvRqst messages are issued, using UDP, following these prioritized rules: 1. A UA issues a request to a DA which it has been configured with by DHCP. 2. A UA issues requests to DAs which it has been statically configured with. 3. A UA uses multicast/convergence SrvRqsts to discover DAs, then uses that set of DAs. A UA that does not know of any DAs SHOULD retry DA discovery once every CONFIG_DA_FIND seconds. 4. A UA with no knowledge of DAs sends requests using multicast convergence to SAs. SAs unicast replies to UAs according to the multicast convergence algorithm. UAs and SAs are configured with a list of scopes to use according to these prioritized rules: Guttman,Perkins,Veizades,Day Expires 30 January 1999 [Page 10]
Internet Draft Service Location Protocol, Version 2 30 July 1998 1. With DHCP. 2. With static configuration. The static configuration may be explicitely set to NO SCOPE for UAs, if the User Selectable Scope model is used. See section 11.2. 3. In the absense of configuration, the agent's scope is "DEFAULT". A UA MUST issue requests with one or more of the scopes it has been configured to use. A UA which has been statically configured with NO SCOPE LIST will use DA or SA discovery to determine its scope list dynamically. In this case it uses an empty scope list to discover DAs and possibly SAs. Then it uses the scope list it obtains from DAAdverts and possibly SAAdverts in subsequent requests.) The SA MUST register all its services with any DA it discovers, if the DA advertises any of the scopes it has been configured with. A SA obtains information about DAs as a UA does. In addition, the SA MUST listen for multicast unsolicited DAAdverts. The SA registers by sending SrvReg messages to DAs, which reply with SrvReg messages to indicate success. SAs register in ALL the scopes they were configured to use. 6.1. Use of Ports, UDP, and Multicast The Service Location Protocol uses multicast by default. The reserved listening port for SLP is 427. This is the destination port for all SLP messages. SLP messages MAY be transmitted on an ephemeral port. Replies and acknowledgements are sent to the port from which the request was issued. The default maximum transmission unit for UDP messages is 1400 bytes. If a SLP message does not fit into a UDP datagram it MUST be truncated to fit, and the OVERFLOW flag is set in the reply message. A UA which receives a truncated message MAY open a TCP connection (see section 6.2) with the DA or SA and retransmit the request, using the same XID. It MAY also attempt to make use of the truncated reply or reformulate a more restrictive request which will result in a smaller reply. SLP Requests messages are multicast to The Administratively Scoped SLP Multicast [18] address, which is 239.255.255.253. The default TTL to use for multicast is 32. In isolated networks, broadcasts will work in place of multicast. To that end, SAs SHOULD and DAs MUST listen for broadcast Service Guttman,Perkins,Veizades,Day Expires 30 January 1999 [Page 11]
Internet Draft Service Location Protocol, Version 2 30 July 1998 Location messages at port 427. This allows UAs which do not support multicast the use of Service Location on isolated networks. Setting multicast TTL to less than 32 (the default) limits the range of SLP discovery in a network, and localizes service information in the network. 6.2. Use of TCP A SrvReg or SrvDeReg may be too large to fit into a datagram. To send such large SLP messages, a TCP (unicast) connection MUST be established. To avoid the need to implement TCP, one MUST insure that: - UAs never issue requests larger than the Path MTU. SAs can omit TCP support only if they never have to receive unicast requests longer than the path MTU. - UAs can accept replies with the 'OVERFLOW' flag set, and make use of the first result included, or reformulate the request. - Ensure that a SA can send a SrvRply, SrvReg, or SrvDeReg in a single datagram. This means limiting the size of URLs, the number of attributes and the number of authenticators transmitted. DAs MUST be able to respond to UDP and TCP requests, as well as multicast DA Discovery SrvRqsts. SAs MUST be able to respond to TCP unless the SA will NEVER receive a request or send a reply which will exceed a datagram in size (e.g., some embedded systems). A TCP connection MAY be used for a single SLP transaction, or for multiple transactions. Since there are length fields in the message headers, SLP Agents can send multiple requests along a connection and read the return stream for acknowledgments and replies. The initiating agent SHOULD close the TCP connection. The DA SHOULD wait at least CONFIG_CLOSE_CONN seconds before closing an idle connection. DAs and SAs SHOULD close an idle TCP connection after CONFIG_CLOSE_CONN seconds to ensure robust operation, even when the initiating agent neglects to close it. See Section 14 for timing rules. Guttman,Perkins,Veizades,Day Expires 30 January 1999 [Page 12]
Internet Draft Service Location Protocol, Version 2 30 July 1998 6.3. Retransmission of SLP messages Requests to SAs are multicast repeatedly (with a recommended wait interval of CONFIG_MC_RETRY) until there are no new responses, or CONFIG_MC_MAX seconds have elapsed. DA discovery requests use different timing for repeated requests, CONFIG_DA_RETRY. Multicast requests SHOULD be reissued over 15 seconds (say 3 times total) until a result has been obtained. UAs need only wait till they obtain the first reply which matches their request. Unicast requests (SrvReg or SrvRqst) to a DA should be retried until either a response (which might be an error) has been obtained, or for 5 seconds. When SLP SrvRqst, SrvTypeRqst, and AttrRqst messages are multicast, they contain a <PRList> of previous responders. Initially the <PRList> is empty. The message SHOULD be retransmitted until the <PRList> causes no further responses to be elicited or the previous responder list and the request will not fit into a single datagram. Retransmission is not required if the requesting agent is prepared to use the 'first reply' instead of 'as many replies as possible within a bounded time interval.' Any DA or SA which sees its address in the <PRList> MUST NOT respond to the request. UAs which retransmit a request use the same XID. This allows a DA or SA to cache its reply to the original request and then send it again, should a duplicate request arrive. This cached information should only be held very briefly. XIDs SHOULD be randomly chosen to avoid duplicate XIDs in requests if UAs restart frequently. 6.4. Strings in SLP messages The escape character is a backslash (UTF8 0x5c) followed by the two hexadecimal digits of the escaped character. Only reserved characters are escaped. For example, a comma (UTF8 0x29) is escaped as `\29', and a backslash `\' is escaped as `\5c'. String lists used in SLP define the comma to be the delimiter between list elements, so commas in data strings must be escaped in this manner. Backslashes are the escape character so they also must always be escaped when included in a string literally. String comparison for order and equality in SLP MUST be case insensitive inside the 0x00-0x7F subrange of UTF8 (which corresponds to ASCII character encoding) Case insensitivity SHOULD be supported throughout the entire UTF8 encoded Unicode [6] character set. Guttman,Perkins,Veizades,Day Expires 30 January 1999 [Page 13]
Internet Draft Service Location Protocol, Version 2 30 July 1998 White space (SPACE, CR, LF, TAB) internal to a string value is folded to a single SPACE character for the sake of string comparisons. White space preceding or following a string value is ignored for the purposes of string comparison. For example, " Some String " matches "SOME STRING". String comparisons (using comparison operators such as `<=' or `>=') are done using lexical ordering in UTF8 encoded characters, not using any language specific rules. The reserved character `*' may precede, follow or be internal to a string value in order to indicate substring matching. The query including this character matches any character sequence which conforms to the letters which are not wildcarded. 7. Errors If the Error Code in a SLP reply message is nonzero, the rest of the message MAY be truncated. No data is necessarily transmitted or should be expected after the header and the error code, except possibly for some optional extensions to clarify the error, for example as in section 13.1. Errors are only returned for unicast requests. Multicast requests are silently discarded if they result in an error. LANGUAGE_NOT_SUPPORTED = 1: There is data for the service type in the scope in the AttrRqst or SrvRqst, but not in the requested language. PARSE_ERROR = 2: The message fails to obey SLP syntax. INVALID_REGISTRATION = 3: The SrvReg has problems -- e.g., a zero lifetime or an omitted language tag. SCOPE_NOT_SUPPORTED = 4: The SLP message did not include a scope in its <scope-list> supported by the SA or DA. AUTHENTICATION_UNKNOWN = 5: The DA or SA receives a request for a cryptographic algorithm or key generation it cannot support. AUTHENTICATION_ABSENT = 6: The DA expected URL and ATTR authentication in the SrvReg and did not receive it. AUTHENTICATION_FAILED = 7: The DA detected an authentication error in an Authentication block. VER_NOT_SUPPORTED = 9: Unsupported version number in message header. INTERNAL_ERROR = 10: The DA (or SA) is too sick to respond. DA_BUSY_NOW = 11: UA or SA SHOULD retry, using exponential back off. OPTION_NOT_UNDERSTOOD = 12: The DA (or SA) received an unknown option from the mandatory range (see section 9.1). INVALID_UPDATE = 13: The DA received a SrvReg without FRESH set, for an unregistered service or with inconsistent Service Types. Guttman,Perkins,Veizades,Day Expires 30 January 1999 [Page 14]
Internet Draft Service Location Protocol, Version 2 30 July 1998 MSG_NOT_SUPPORTED = 14: The SA received an AttrRqst or SrvTypeRqst and does not support it. INVALID_LIFETIME = 15: The SA registered a service with a lifetime the DA has disallowed in its DAAdvert. 8. Required SLP Messages SLP messages all begin with the following header: 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Version | Function-ID | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Length, contd.|O|F|R| rsvd | Language Tag Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Next Extension Offset | XID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Language Tag \ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Message Type Abbreviation Function-ID Service Request SrvRqst 1 Service Reply SrvRply 2 Service Registration SrvReg 3 Service Deregister SrvDeReg 4 Service Acknowledge SrvAck 5 Attribute Request AttrRqst 6 Attribute Reply AttrRply 7 DA Advertisement DAAdvert 8 Service Type Request SrvTypeRqst 9 Service Type Reply SrvTypeRply 10 SA Advertisement SAAdvert 11 SAs and UAs MUST support SrvRqst, SrvRply and DAAdvert. SAs MUST also support SrvReg, SAAdvert and SrvAck. For UAs and SAs, support for other messages are OPTIONAL. - Length is the length of the entire SLP message, header included. - The flags are: OVERFLOW (0x80) is set when a message's length exceeds what can fit into a datagram. FRESH (0x10) is set on every new SrvReg. REQUEST MCAST (0x08) is set when multicasting or broadcasting requests. Rsvd bits MUST be 0. - Lang Tag Length indicates the length of the Language Tag field. - Next Extension Offset is set to 0 unless extensions are used. The first extension begins at 'offset' bytes, from the message's Guttman,Perkins,Veizades,Day Expires 30 January 1999 [Page 15]
Internet Draft Service Location Protocol, Version 2 30 July 1998 beginning, after the SLP message data. See Section 9.1 for how to interpret unrecognized options. - XID is set to a unique value for each unique request. If the request is retransmitted, the same XID is used. Replies set the XID to the same value as the xid in the request. Only unsolicited DAAdverts are sent with an XID of 0. - Language Tag conforms to [7]. The Language Tag in a reply MUST be the same as the Language Tag in the request. This field must be encoded 1*8ALPHA ["-" 1*8ALPHA]. If an option is specified, and not included in the message, the receiver MUST respond with a PARSE_ERROR. 8.1. Service Request 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Service Location header (function = SrvRqst = 1) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | length of <PRList> | <PRList> String \ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | length of <service-type> | <service-type> String \ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | length of <scope-list> | <scope-list> String \ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | length of predicate string | Service Request <predicate> \ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ In order for a Service to match a SrvRqst, it must belong to at least one requested scope, support the requested service type, and match the predicate. If the predicate is present, the language of the request (ignoring the dialect part of the Language Tag) must match the advertised service. <PRList> is the Previous Responder List. This <string-list> contains either fully qualified domain names or dotted decimal notation IP (v4) addresses, and is iteratively multicast to obtain all possible results (see Section 6.3). UAs SHOULD implement this discovery algorithm. SAs MUST use this to discover all available DAs in their scope, if they are not already configured with DA addresses by some other means. A SA silently drops all requests which include the SA's address in the <PRList>. Once a <PRList> plus the request exceeds the path MTU, multicast convergence stops. This algorithm is not intended to find all instances; it finds 'enough' to provide useful results. Guttman,Perkins,Veizades,Day Expires 30 January 1999 [Page 16]
Internet Draft Service Location Protocol, Version 2 30 July 1998 The <scope-list> is a <string-list> of configured scope names. SAs and DAs which have been configured with any of the scopes in this list will respond. DAs and SAs MUST reply to unicast requests with a SCOPE_NOT_SUPPORTED error if the <scope-list> is omitted or fails to include a scope they support (see Section 11). The only exceptions to this are described in Section 11.2. The <service-type> string is discussed in Section 4. Normally, a SrvRqst elicits a SrvRply. There are two exceptions: If the <service-type> is set to "service:directory-agent", DAs respond to the SrvRqst with a DAAdvert (see Section 8.5.) If set to "service:service-agent", SAs respond with a SAAdvert (see Section 8.6.) The <predicate> is a LDAPv3 search filter [16]. This field may be omitted if services are to be discovered simply by type and scope. Otherwise, services are discovered which satisfy the <predicate>. If present, it is compared to each registered service. If the attribute in the filter has been registered with multiple values, the filter is compared to each value and the results are ORed together, i.e., "(x=3)" matches a registration of (x=1,2,3); "(!(Y=0))" matches (y=0,1) since Y can be nonzero. Note the matching is case insensitive. Keywords (i.e., attributes without values) are matched with a "presence" filter, as in "(keyword=*)". An incoming request term MUST have the same type as the attribute in a registration in order to match. Thus, "(x=33)" will not match 'x=true', etc. while "(y=foo)" will match 'y=FOO'. "(|(x=33)(y=foo))" will be satisfied, even though "(x=33)" cannot be satisfied, because of the `|' (boolean disjunction). Wildcard matching can ONLY be done with the '=' filter. In any other case, a PARSE_ERROR is returned. Request terms which include wildcards are interpreted to be Strings. That is, (x=34*) would match 'x=34foo', but not 'x=3432' since the first value is a String while the second value is an Integer; Strings don't match Integers. Examples of Predicates follow. <t> indicates the service type of the SrvRqst, <s> gives the <scope-list> and <p> is the predicate string. <t>=service:http <s>=DEFAULT <p>= (empty string) This is a minimal request string. It matches all http services advertised with the default scope. <t>=service:pop3 <s>=SALES,DEFAULT <p>=(user=wump) This is a request for all pop3 services available in the SALES or DEFAULT scope which serve mail to the user `wump'. Guttman,Perkins,Veizades,Day Expires 30 January 1999 [Page 17]
Internet Draft Service Location Protocol, Version 2 30 July 1998 <t>=service:backup <s>=BLDG 32 <p>=(&(q<=3)(speed>=1000)) This returns the backup service which has a queue length less than 3 and a speed greater than 1000. It will return this only for services registered with the BLDG 32 scope. DAs are discovered by sending a SrvRqst with the service type set to "service:directory-agent". If a predicate is included in the SrvRqst, the DA SHOULD respond only if the predicate can be satisfied with the DA's attributes. The <scope-list> SHOULD contain all scopes configured for the service. If omitted, see Section 11.2. For example: <t>=service:directory-agent <s>=DEFAULT <p>= This returns DAAdverts for all DAs in the DEFAULT scope. 8.2. Service Reply 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Service Location header (function = SrvRply = 2) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Error Code | URL Entry count | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | <URL Entry 1> ... <URL Entry N> \ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ The service reply contains one or more URL entries (see Section 4.3) that satisfy a SrvRqst. If the reply overflows, the UA MAY simply use the first URL Entry in the list. A URL obtained by SLP may not be cached longer than Lifetime seconds, unless there is a URL Authenticator block present. In that case, the cache lifetime is indicated by the Timestamp in the URL Authenticator (see Section 9.2). One authentication block is returned for each protected scope the service was registered in which was present in the <scope-list> of the SrvRqst. If a SrvRply is sent by UDP, a URL Entry MUST NOT be included unless it fits entirely without truncation. Guttman,Perkins,Veizades,Day Expires 30 January 1999 [Page 18]
Internet Draft Service Location Protocol, Version 2 30 July 1998 8.3. Service Registration 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Service Location header (function = SrvReg = 3) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | <URL-Entry> \ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | length of service type string | <service-type> \ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | length of <scope-list> | <scope-list> \ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | length of attr-list string | <attr-list> \ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |# of AttrAuths |(if present) Attribute Authentication Blocks...\ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ The <entry> is a URL Entry (see section 4.3). The Lifetime defines how long a DA can cache the registration. SAs SHOULD reregister before this lifetime expires (but SHOULD NOT more often than once per second). The Lifetime MAY be set to any value between 0 and 0xffff (maximum, around 18 hours). Long-lived registrations remain stale longer if the service fails and the SA does not deregister the service. The <service-type> defines the service type of the URL to be registered, regardless of the scheme of the URL. The <scope-list> MUST be contain the names of all scopes configured for the SA, which the DA it is registering with supports. The default value for the <scope-list> is "DEFAULT" (see Section 11). The SA MUST register consistently with all DAs. If a SA is configured with scopes X and Y and there are three DAs, whose scopes are "X", "Y" and "X,Y" respectively, the SA will register the with all three DAs in their respective scopes. All future updates and deregistrations of the service must be sent to the same set of DAs in the same scopes the service was initially registered in. The <attr-list>, if present, specifies the attributes and values to be associated with the URL by the DA (see Section 5). If the registration occurs in a protected scope, an Authentication block (see Section 9.2) is included for each protected scope, for each Key Generation Number supported. It is calculated over the ordered tuple (16-bit length of <attr-list>, <attr-list>, timestamp, 16-bit length of scope string, scope string), where the timestamp is taken from the Authentication block. Guttman,Perkins,Veizades,Day Expires 30 January 1999 [Page 19]
Internet Draft Service Location Protocol, Version 2 30 July 1998 A registration with the FRESH flag set will replace *entirely* any previous registration for the same URL in the same language. If the FRESH flag is not set, the registration is an "incremental" registration (see Section 9.4). 8.4. Service Acknowledgment 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Service Location header (function = SrvAck = 4) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Error Code | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ A DA returns a SrvAck to an SA after a SrvReg. It carries only a two byte Error Code (see Section 7). 8.5. Directory Agent Advertisement 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Service Location header (function = DAAdvert = 8) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | DA Stateless Boot Timestamp | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Length of URL | URL \ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Length of <scope-list> | <scope-list> \ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Length of <attr-list> | <attr-list> \ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | # Auth Blocks | Authentication block (if any) \ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ DAs respond with DAAdverts only to SrvRqsts with the MCAST RQST flag set. The <scope-list> of the SrvRqst must either be omitted or include a scope which the DA supports. The DA Stateless Boot Timestamp indicates the state of the DA (see section 12.2.2). The DA MAY include a list of its attributes in the DAAdvert. This list SHOULD be kept short, as the DAAdvert must fit into a datagram in order to be multicast. A potential scaling problem occurs in SLPv2 if SAs choose too low a Lifetime. In this case, an onerous amount of reregistration occurs Guttman,Perkins,Veizades,Day Expires 30 January 1999 [Page 20]
Internet Draft Service Location Protocol, Version 2 30 July 1998 as more services are deployed. SLPv2 allows DAs to control SAs frequency of registration. A DA MAY reissue a DAAdvert with a new set of attributes at any time, to change the reregistration behavior of SAs. These apply only to subsequent registrations; existing service registrations with the DA retain their registered lifetimes. If the DAAdvert includes the attribute "min-lifetime" it MUST be set to a single Integer value. If this attribute is present SAs MUST NOT set registered service lifetimes to be shorter than this value (in seconds). Further, SAs MUST NOT refresh the advertisement less often than 80% of this interval. If the DAAdvert includes the attribute "max-lifetime", it MUST be set to a single Integer value. SAs MUST NOT set registered service lifetimes to be longer than this value (in seconds). If a registered lifetime is below the min-lifetime or above the max-lifetime advertised by the DA it will reject the registration and return a INVALID_LIFETIME error in the SrvAck. The URL is "service:directory-agent://"<addr> of the DA, where <addr> is the dotted decimal numeric address of the DA. The <scope-list> of the DA MUST NOT be null. The DAAdvert MAY contain an authenticator, which will be generated using a DA Advertising private key. This authenticator is calculated over the following ordered tuple: (DA Stateless Boot Timestamp, Length of URL, URL, Length of <attr-list>, <attr-list>, Length of <scope-list>, <scope-list>, Timestamp), where the Timestamp is taken from the Authentication block. The Protected Scope String of the authentication block is omitted in a DAAdvert (i.e., the Protected Scope String Length is zero). The Authenticator Timestamp is set to the time when the DAAdvert expires (may no longer be cached). If multiple Key Generation Numbers are supported for DAAdvert authenication, the DA MUST include one Authentication Block for each generation number. See Section 9.2. UAs SHOULD be configured with DA Advertisement public keys so they can verify the authenticity of DAAdverts. If the UA detects a authentication failure of the DAAdvert, the UA MUST discard it. 8.6. Service Agent Advertisement User Agents MUST NOT solicit SA Advertisements if they have been configured to use a particular DA, if they have been configured with a <scope-list> or if DAs have been discovered. UAs solicit SA Advertisements only when they are explicitly configured to use User Selectable scopes (see Section 11.2) in order to discover the scopes that SAs support. This allows UAs without scope configuration Guttman,Perkins,Veizades,Day Expires 30 January 1999 [Page 21]
Internet Draft Service Location Protocol, Version 2 30 July 1998 to make use of either DAs or SAs without any functional difference except performance. A SA MAY be configured with attributes, and SHOULD support the attribute 'service-type' whose value is all the service types of services represented by the SA. SAs MUST NOT respond if the SrvRqst predicate is not satisfied. For example, only SAs offering 'nfs' services SHOULD respond with a SAAdvert to a SrvRqst for service type "service:service-agent" which includes a predicate "(service-type=nfs)". 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Service Location header (function = SAAdvert = 11) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Length of URL | URL \ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Length of <scope-list> | <scope-list> \ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Length of <attr-list> | <attr-list> \ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | # auth blocks | authentication block (if any) \ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ The SA responds only to multicast SA discovery requests which either include no <scope-list> or a scope which they are configured to use. The SAAdvert MAY include a list of attributes the SA supports. This attribute list SHOULD be kept short so that the SAAdvert will not exceed the path MTU in size. The URL is "service:service-agent://"<addr> of the SA, where <addr> is the dotted decimal numeric address of the SA. The <scope-list> of the SA MUST NOT be null. The SAAdvert contains one URL Authentication block for each protected scope the SA supports, for every Key Generation Number the SA supports. If the UA can verify the protected scope SAAdvert, and the SAAdvert fails to be verified, the UA MUST discard it. The authenticator is calculated over the following ordered tuple: (Length of URL, URL, Length of <attr-list>, <attr-list>, Length of <scope-list>, <scope-list>). The protected scope field of the authentication block is set to the protected scope the authentication block corresponds to. The Authenticator Timestamp is set to the time when the SAAdvert expires (may no longer be cached). Guttman,Perkins,Veizades,Day Expires 30 January 1999 [Page 22]
Internet Draft Service Location Protocol, Version 2 30 July 1998 9. Optional Features The features described in this section are not mandatory. Some are useful for interactive use of SLP (where a user rather than a program will select services, using a browsing interface for example) and for scalability of SLP to larger networks. 9.1. Service Location Protocol Extensions The format of a Service Location Extension is: 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 | Extension Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Extension Data \ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ The offset to next extension is 0 if there are no extensions following or is set to the length of the current Extension Data. If the offset is 0, the length of the current Extension Data is determined implicitly by use of the total length of the SLP message as given in the SLP message header. Extension IDs are assigned in the following way: 0x0000-0x3FFF Standardized. Optional to implement. Ignore if unrecognized. 0x4000-0x7FFF Standardized. Mandatory to implement. A UA or SA which receives this option in a reply and does not understand it MUST silently discard the reply. A DA or SA which receives this option in a request and does not understand it MUST return an OPTION_NOT_UNDERSTOOD error. 0x8000-0x8FFF For private use (not standardized). Optional to implement. Ignore if unrecognized. 0x9000-0xFFFF Reserved. Extensions defined in this document are in Section 13. See section 16 for procedures that are required when specifying new SLP extensions. Guttman,Perkins,Veizades,Day Expires 30 January 1999 [Page 23]
Internet Draft Service Location Protocol, Version 2 30 July 1998 9.2. Authentication Blocks 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Block Structure Descriptor | Authentication Block Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Key Generation Number | Protected Scope String Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ \ Protected Scope String \ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Timestamp | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Structured Authentication Block ... \ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Authentication blocks are returned with certain SLP messages to verify that the contents have not been modified, and have been transmitted by an authorized agent. The authentication data (contained in the Structured Authentication Block) is typically case sensitive. Even though SLP registration data (e.g., attribute values) are typically are not case sensitive even for protected scopes, the case of the registration data has to be preserved by the registering DA so that UAs will be able to verify the authentication data. The Block Structure Descriptor (BSD) identifies the format of the Authenticator which follows. BSDs 0x0000-0x7FFF will be maintained by IANA. BSDs 0x8000-0x8FFF are for private use. The Authentication Block Length is the length of the entire block, starting with the BSD. The Key Generation Number (KGN) identifies the 'generation' of the key associated with the Protected Scope string which follows. The value 0 MUST NOT be used and the values 1-255 are reserved. There may be several 'key generations' deployed in a network simultaneously. This allows gradual rekeying of a network. For example, a network is keyed with keys for protected scope 'foo' with KGN 1022. Later, SAs are rekeyed to also have KGN '1023'. Eventually, when all UAs and DAs in the network are rekeyed with keys with KGN '1023', SAs need no longer support KGN '1022' keys. A SA which supports multiple KGNs for a protected scope MUST register Authentication Blocks generated with each KGN with DAs. DAs and SAs MUST include authentication blocks in each KGN associated with a Guttman,Perkins,Veizades,Day Expires 30 January 1999 [Page 24]
Internet Draft Service Location Protocol, Version 2 30 July 1998 protected scope unless the UA which initiated the request includes a Cryptographic Request Option specifying a particular KGN. Note that many SLP messages are sent using UDP datagrams. These have a limited payload so few Authentication Blocks will fit into a SLP message. For this reason, as few Key Generations as possible should be supported simultaneously: Ideally only ONE should be used except during transitions. The Protected scope string identifies the keying material to be used by agents to verify the signature data in the Structured Authentication Block. The Timestamp is the time that the authenticator expires (to prevent replay attacks.) The Timestamp is a 32-bit unsigned fixed-point number of seconds relative to 0h on 1 January 1900, in NTP format [19]. SAs and DAs MAY use this value to indicate how long they expect the service to be available for (for instance, in DAAdverts and SAAdverts). All SLP agents MUST implement DSA [22] (BSD=0x0002). SAs MUST register services with DSA authentication blocks, and they MAY register them with other authentication blocks using other algorithms. SAs MUST use DSA authentication blocks in SrvDeReg messages and DAs MUST use DSA authentication blocks in unsolicited DAAdverts. 9.2.1. MD5 with RSA in Authentication Blocks BSD=0x0001 indicates that md5WithRSAEncryption is selected as the authentication algorithm for the Structured Authentication Block. The Authentication Block will start with the ASN.1 Distinguished Encoding (DER) [11] for "md5WithRSAEncryption", which has as its value the bytes (MSB first in hex): "30 0d 06 09 2a 86 48 86 f7 0d 01 01 04 05 00" This is then immediately followed by an ASN.1 Distinguished Encoding (as a "Bitstring") of the RSA encryption (using the protected scope's private key) of a bitstring consisting of the OID for "MD5" concatenated by the MD5 [23] message digest computed over the fields above. The exact construction of the MD5 OID and digest can be found in RFC 1423 [8]. Guttman,Perkins,Veizades,Day Expires 30 January 1999 [Page 25]
Internet Draft Service Location Protocol, Version 2 30 July 1998 9.2.2. DSA with SHA-1 in Authentication Blocks BSD=0x0002 is defined to be DSA with SHA-1. The signature calculation is defined by [22]. The signature format conforms to that in the X.509 v3 certificate: 1. The signature algorithm identifier (an OID) 2. The signature value (an octet string) 3. The certificate path. All data is represented in ASN.1 encoding: id-dsa-with-sha1 ID ::= { iso(1) member-body(2) us(840) x9-57 (10040) x9cm(4) 3 } i.e., the ASN.1 encoding of 1.2.840.10040.4.3 followed immediately by: Dss-Sig-Value ::= SEQUENCE { r INTEGER, s INTEGER } i.e., the binary ASN.1 encoding of r and s computed using DSA and SHA-1. This is followed by a certificate path, as defined by X.509 [12], [2], [3], [4], [5]. 9.2.3. Keyed HMAC with MD5 in Authentication Blocks BSD=0x0003 is defined to be HMAC [17] using keyed-MD5 [23]. Given a secret key K and the data to authenticate, the Authentication Block is computed as follows: 1. opad := 0x36363636363636363636363636363636 (128 bits) 2. ipad := 0x5C5C5C5C5C5C5C5C5C5C5C5C5C5C5C5C (128 bits) 3. zero_extended_key := K extended by zeroes to be 128 bits long 4. opadded_key := zero_extended_key XOR opad 5. ipadded_key := zero_extended_key XOR ipad 6. HMAC_result := MD5 (opadded_key , MD5 (ipadded_key, data)) The authenticator is the 128-bit value HMAC_result. Note that this authentication scheme works for peer-to-peer implementations (where hosts can both verify and generate authenticators) but not for client-server applications where clients are NOT trusted to create authenticators for services of a protected scope. In this case, public key cryptography is used. Guttman,Perkins,Veizades,Day Expires 30 January 1999 [Page 26]
Internet Draft Service Location Protocol, Version 2 30 July 1998 9.3. Authentication of a SrvRply A SrvRply containing a URL from a service in a protected scope MUST include an Authentication Block for each protected scope. The Authentication data MUST be calculated over the following ordered tuple: (Length of URL, URL, Timestamp, 16-bit Length of Scope String, Scope String). The Authentication block is calculated according to the algorithm indicated by the BSD value using the cryptographic key identified by the protected scope string and Key Generation Number in the Authentication Block. 9.4. Incremental Service Registration Incremental registrations update attribute values for a previously registered service. Incrmental service registrations are useful when only a single attribute has changed, for instance. In an incremental registration, the FRESH flag in the SrvReg header is NOT set. The new registration's attributes replace the previous registration's, but do not affect attributes which were included previously and are not present in the update. For example, suppose service:x://a.org has been registered with attributes A=1, B=2, C=3. If an incremental registration comes for service:x://a.org with attributes C=30, D=40, then the attributes for the service after the update are A=1, B=2, C=30, D=40. Incremental registrations MUST NOT be performed for services registered in protected scopes. These must be registered with ALL attributes, with the FRESH flag in the SrvReg header set. DAs which receive such registration messages return an AUTHENTICATION_FAILED error. If the FRESH flag is not set and the DA does not have a prior registration for the service, the incremental registration fails with error code INVALID_UPDATE. The SA MUST use the same <scope-list> in an update message as was used in the prior registration. If this is not done, the DA returns a SCOPE_NOT_SUPPORTED error. In order to change the scope of a service advertisement it MUST be deregistered first and reregistered with a new <scope-list>. The SA MUST use the same <service-type> in an update message as was used in a prior registration of the same URL. If this is not done, the DA returns an INVALID_UPDATE error. Guttman,Perkins,Veizades,Day Expires 30 January 1999 [Page 27]
Internet Draft Service Location Protocol, Version 2 30 July 1998 9.5. Tag Lists Tag lists are used in SrvDeReg and AttrReq messages. The syntax of a <tag-list> item is: tag-filter = simple-tag / substring simple-tag = 1*filt-char substring = [initial] any [final] initial = 1*filt-char any = `*' *(filt-char `*') final = 1*filt-char filt-char = Any character excluding <reserved> and <bad-tag> (see grammar in Section 5). Wild card characters in a <tag-list> item match arbitrary sequences of characters. For instance "*bob*" matches "some bob I know", "bigbob", "bobby" and "bob". 10. Optional SLP Messages The additional requests provide features for user interaction and for efficient updating of service advertisements with dynamic attributes. 10.1. Service Type Request The Service Type Request (SrvTypeRqst) allows a UA to discover all types of service on a network. This is useful for general purpose service browsers. 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Service Location header (function = SrvTypeRqst = 9) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | length of PRList | <PRList> String \ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | length of Naming Authority | <Naming Authority String> \ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | length of <scope-list> | <scope-list> String \ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ The <PRList> list and <scope-list> are interpreted as in Section 8.1. The Naming Authority string, if present in the request, will limit the reply to Service Type strings with the specified Naming Guttman,Perkins,Veizades,Day Expires 30 January 1999 [Page 28]
Internet Draft Service Location Protocol, Version 2 30 July 1998 Authority. If the Naming Authority string is absent, the IANA registered service types will be returned. If the length of the Naming Authority is set to 0xFFFF, the Naming Authority string is omitted and ALL Service Types are returned, regardless of Naming Authority. 10.2. Service Type Reply 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Service Location header (function = SrvTypeRply = 10) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Error Code | length of <srvType-list> | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | <srvtype--list> \ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ The service-type Strings (as described in Section 4.1) are provided in <srvtype-list>, which is a <string-list>. If a service type has a Naming Authority other than IANA it MUST be returned following the service type string and a `.' character. Service types with the IANA Naming Authority do not include a Naming Authority string. 10.3. Attribute Request The Attribute Request (AttrRqst) allows a UA to discover attributes of a given service (by supplying its URL) or for an entire service type. The latter feature allows the UA to construct a query for an available service by selecting desired features. The UA may request that all attributes are returned, or only a subset of them. 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Service Location header (function = AttrRqst = 6) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | length of PRList | <PRList> String \ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | length of URL | URL \ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | length of <scope-list> | <scope-list> string \ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | length of <tag-list> string | <tag-list> string \ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Guttman,Perkins,Veizades,Day Expires 30 January 1999 [Page 29]
Internet Draft Service Location Protocol, Version 2 30 July 1998 The <PRList> and <scope-list> are interpreted as in Section 8.1. The URL field can take two forms. It can simply be a Service Type (see Section 4.1), such as "http" or "service:tftp". In this case, all attributes and the full range of values for each attribute of all services of the given Service Type is returned. The URL field may alternatively be a full URL, such as "service:printer:lpr://igore.wco.ftp.com:515/draft" or "nfs://max.net/znoo". In this, only the registered attributes for the specified URL are returned. The <tag-list> field is a <string-list> of attribute tags, as defined in Section 9.5 which indicates the attributes to return in the AttrRply. If <tag-list> is omitted, all attributes are returned. <tag-list> MUST be omitted and a full URL MUST be included when attributes are requested in a protected scope from a DA, otherwise the DA will reply with an AUTHENTICATION_FAILED error. 10.4. Attribute Reply 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Service Location header (function = AttrRply = 7) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Error Code | length of <attr-list> | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | <attr-list> \ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | # Auth Blocks |(if present) Attribute Authentication Blocks...\ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ The format of the <attr-list> and the Authentication Block is as specified for SrvReg (see Section 9.2). Attribute replies SHOULD be returned with the original case of the string registration intact, as they are likely to be human readable. In the case where the AttrRqst was by service type, all attributes defined for the service type, and all their values are returned. Although white space is folded for string matching, attribute tags and values MUST be returned with their original white space preserved. Only one copy of each attribute tag or String value should be returned, arbitrarily choosing one version (with respect to upper and lower case and white space internal to the strings): Duplicate Guttman,Perkins,Veizades,Day Expires 30 January 1999 [Page 30]
Internet Draft Service Location Protocol, Version 2 30 July 1998 attributes and values SHOULD be removed. An arbitrary version of the string value and tag name is chosen for the merge. For example: "(A=a a,b)" merged with "(a=A A,B)" may yield "(a=a a,B)". One Attribute Authentication Block is returned for each protected scope in the <scope-list>, for each Key Generation number supported. Note that the <attr-list> returned from a DA in a protected scope MUST be identical to the <attr-list> registered by a SA, in order for the authentication to be successful. 10.5. Attribute Request/Reply Examples Suppose that printer services have been registered as follows: Registered Service: URL = service:printer:lpr://igore.wco.ftp.com/draft scope-list = Development Lang. Tag = en Attributes = (Name=Igore),(Description=For developers only), (Protocol=LPR),(location-description=12th floor), (Operator=James Dornan \3cdornan@monster\3e), (media-size=na-letter),(resolution=res-600),x-OK URL = service:printer:lpr://igore.wco.ftp.com/draft scope-list = Entwicklung Lang. Tag = de Attributes = (Name=Igore),(Beschreibung=Nur fuer Entwickler), (Protocol=LPR),(Standort-beschreibung=13te Etage), (Techniker=James Dornan \3cdornan@monster\3e), (Format=na-letter),(Resolution=res-600),x-OK URL = service:printer:http://not.wco.ftp.com/cgi-bin/pub-prn scope-list = Development Lang. Tag = en Attributes = (Name=Not),(Description=Experimental IPP printer), (Protocol=http),(location-description=QA bench), (media-size=na-letter),(resolution=other),x-BUSY Notice the first printer, "Igore" is registered in both English and German. The `<' and `>' characters in the Operator attribute value which are part of the Email address had to be escaped, as they are reserved characters for values. The string "PROTOCOL" is 'literal' so it is not translated to different languages, see [15]. The attribute Request: Guttman,Perkins,Veizades,Day Expires 30 January 1999 [Page 31]
Internet Draft Service Location Protocol, Version 2 30 July 1998 URL = service:printer:lpr://igore.wco.ftp.com/draft scope-list = Entwicklung Lang. Tag = de tag-list = Resolution,St* receives the Attribute Reply: (Standort-beschreibung=13te Etage),(Resolution=res-600) The attribute Request: URL = service:printer scope-list = Development Lang. Tag = en tag-list = x-*,resolution,protocol receives an Attribute Reply containing: (protocols=http,LPR),(resolution=res-600,other),x-OK,x-BUSY The first request is by service instance and returns the requested values, in German. The second request is by abstract service type (see Section 4) and returns values from both "Igore" and "Not". 10.6. Service Deregistration A DA deletes a service registration when its Lifetime expires. Services SHOULD be deregistered when they are no longer available, rather than leaving the registrations to time out. 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Service Location header (function = SrvDeReg = 5) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Length of <scope-list> | <scope-list> \ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | URL Entry \ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Length of <tag-list> | <tag-list> \ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ The <scope-list> is a <string-list> (see section 2.1). The SA MUST retry if there is no response from the DA, see Section 12.3. The DA acknowledges a SrvDeReg with a SrvAck. Once the SA receives an acknowledgment indicating success, the service and/or attributes are no longer advertised by the DA. The DA deregisters Guttman,Perkins,Veizades,Day Expires 30 January 1999 [Page 32]
Internet Draft Service Location Protocol, Version 2 30 July 1998 the service or service attributes from every scope specified in the SrvDeReg which it was previously registered in. The SA MUST deregister all services with the same scope list used to register the service with a DA. If this is not done in the SrvDeReg message, the DA returns a SCOPE_NOT_SUPPORTED error. The Lifetime field in the URL Entry is ignored for the purposes of the SrvDeReg. The <tag-list> is a <string-list> of attribute tags to deregister as defined in Section 9.5. If no <tag-list> is present, the SrvDeReg deregisters the service in all languages it has been registered in. If the <tag-list> is present, the SrvDeReg deregisters the attributes whose tags are listed in the tag spec. Services registered in protected scopes MUST NOT include a <tag-list> in a SrvDeReg message: A DA will respond with an AUTHENTICATION_FAILED error in this case. If the service to be deregistered was registered in a protected scope, a URL authentication block for that protected scope and Key Generation Number MUST be included. Otherwise, the DA returns an AUTHENTICATION_ABSENT error is returned. If the message fails to be verified by the DA, an AUTHENTICATION_FAILED error is returned by the DA. 11. Scopes Scopes are sets of services. The primary use of Scopes is to provide the ability to create administrative groupings of services. A set of services may be assigned a scope by network administrators. A client seeking services is configured to use one or more scopes. The user will only discover those services which have been configured for him or her to use. By configuring UAs and SAs with scopes, administrators may provision services. Scopes strings are case insensitive. The default SCOPE string is "DEFAULT". Scopes are the primary means an administrator has to scale SLP deployments to larger networks. When DAs with NON-DEFAULT scopes are present on the network, further gains can be had by configuring UAs and SAs to have a predefined non-default scope. These agents can then perform DA discovery and make requests using their scope. This will limit the number of replies. 11.1. Scope Rules SLP messages which fail to contain a scope that the receiving Agent is configured to use are dropped (if the request was multicast) or a SCOPE_NOT_SUPPORTED error is returned (if the request was unicast). Guttman,Perkins,Veizades,Day Expires 30 January 1999 [Page 33]
Internet Draft Service Location Protocol, Version 2 30 July 1998 Every SrvRqst (except for DA and SA discovery requests), SrvReg, AttrRqst, SrvTypeRqst, DAAdvert, and SAAdvert message MUST include a <scope-list>. A UA MUST unicast its SLP messages to a DA which supports the desired scope, in preference to multicasting a request to SAs. A UA MAY multicast the request if no DA is available in the scope it is configured to use. 11.2. Administrative and User Selectable Scopes All requests and services are scoped. The two exceptions are SrvRqsts for "service:directory-agent" and "service:service-agent". These MAY have a zero-length <scope-list> when used to enable the user to make scope selections. In this case UAs obtain their scope list from DAAdverts (or if DAs are not available, from SAAdverts.) Otherwise, if SAs and UAs are to use any scope other than the default (i.e., "DEFAULT"), the UAs and SAs are configured with lists of scopes to use by system administrators, perhaps automatically by way of DHCP option 78 or 79. Such administrative scoping allows services to be provisioned, so that users will only see services they are intended to see. User configurable scopes allow a user to discover any service, but require them to do their own selection of scope. This is similar to the way AppleTalk [14] and LanManager [21] networking allow user selection of AppleTalk Zone or Windows Workgroups. Note that the two configuration choices are not compatible. One model allows administrators control over service provision. The other delegates this to users (who may not be prepared to do any configuration of their system). 11.3. Protected Scopes A protected scope is identical to a nonprotected scope except that it requires authentication of service information. If a `protected scope' is configured, it must be accompanied by a key for the authentication calculation. Typically, public key cryptography is used to avoid excessive disclosure of any private shared key with a possibly large collection of UAs. In protected scopes, certain SLP functions are restricted: AttrRqst and SrvDeReg messages MUST NOT contain a <tag-list>. DAs MUST verify SrvReg and SrvDeReg messages sent by SAs which select Guttman,Perkins,Veizades,Day Expires 30 January 1999 [Page 34]
Internet Draft Service Location Protocol, Version 2 30 July 1998 protected scopes. UAs MUST verify SrvRply and AttrRply messages sent using protected scopes before returning them to client processes. 12. Directory Agents DAs cache service location and attribute information. They exist to enhance the performance and scalability of SLP. Multiple DAs provide further scalability and robustness of operation, since they can each store service information for the same SAs, in case one of the DAs fails. For use in networks with multiple subnets, a DA provides a centralized store for service information. The DA address can be dynamically configured with UAs and DAs using DHCP, or by using static configuration. Passive detection of DAs by SAs enables services to be advertised consistently among DAs of the same scope. Advertisements expire if not renewed, leaving only transient stale registrations in DAs, even in the case of a failure of a SA. A single DA can support many UAs. UAs send the same requests to DAs that they would send to SAs and expect the same results. DAs reduce the load on SAs, making simpler implementations of SAs possible. UAs be prepared for the possibility that the service information they obtain from DAs is stale. 12.1. Directory Agent Rules When DAs are present, each SA MUST register its services with DAs that support one or more of its scope(s). UAs MUST unicast requests directly to a DA (when scoping rules allow), hence avoiding using the multicast convergence algorithm, to obtain service information. This decreases network utilization and increases the speed at which UAs can obtain service information. DAs MUST flush service advertisements once their lifetime expires or their URL Authentication Block "Timestamp" of expiration is past. DAAdverts MUST include DA Stateless Boot Timestamp, in the same format as the Authentication Block (see Section 9.2). The Timestamp in the Authentication Block indicates the time at which all previous registrations were lost (i.e., the last stateless reboot). The Timestamp is set to 0 in a DAAdvert to notify UAs and SAs that the DA is going down. Guttman,Perkins,Veizades,Day Expires 30 January 1999 [Page 35]
Internet Draft Service Location Protocol, Version 2 30 July 1998 DAs which receive a multicast SrvRqst for the service type "service:directory-agent" MUST silently discard it if the <scope-list> is (a) not omitted and (b) does not include a scope they are configured to use. Otherwise the DA MUST respond with a DAAdvert. DAs MUST respond to AttrRqst and SrvTypeRqst messages (these are OPTIONAL only for SAs, not DAs.) 12.2. Directory Agent Discovery UAs can discover DAs using static configuration, DHCP options 78 and 79, or by multicasting (or broadcasting) Service Requests using the convergence algorithm in Section 6.3. See Section 6 regarding unsolicited DAAdverts. Section 12.2.2 describes how SAs may reduce the number of times they must reregister with DAs in response to unsolicited DAAdverts. DAs MUST send unsolicited DAAdverts once per CONFIG_DA_BEAT. An unsolicited DAAdvert has an XID of 0. SAs MUST listen for DAAdverts, passively, as described in Section 8.5. UAs SHOULD do this. A URL with the scheme "service:directory-agent" indicates the DA's location as defined in Section 8.5. For example: "service:directory-agent://foobawooba.org". The following sections suggest timing algorithms which enhance the scalability of SLP. 12.2.1. Active DA Discovery After a UA or SA restarts, its initial DA discovery request SHOULD be delayed for some random time uniformly distributed from 0 to CONFIG_START_WAIT seconds. The UA or SA sends the DA Discovery request using a SrvRqst, as described in Section 8.1. DA Discovery requests MUST include a Previous Responder List. SrvRqsts for Active DA Discovery SHOULD NOT be sent more than once per CONFIG_DA_FIND seconds. After discoverying a new DA, a SA MUST wait a random time between 0 and CONFIG_REG_ACTIVE seconds before registering their services. Guttman,Perkins,Veizades,Day Expires 30 January 1999 [Page 36]
Internet Draft Service Location Protocol, Version 2 30 July 1998 12.2.2. Passive DA Advertising A DA MUST multicast (or broadcast) an unsolicited DAAdvert every CONFIG_DA_BEAT seconds. CONFIG_DA_BEAT SHOULD be specified to prevent DAAdverts from using more than 1% of the available bandwidth. All UAs and SAs which receive the unsolicited DAAdvert SHOULD examine its DA stateless Boot Timestamp. If it is set to 0, the DA is going down and no further messages should be sent to it. If a SA detects a DA it has never encountered (with a nonzero timestamp,) the SA must register with it. SAs MUST examine the DAAdvert's timestamp to determine if the DA has had a stateless reboot since the SA last registered with it. If so it registers with the DA. SAs MUST wait a random interval between 0 and CONFIG_REG_PASSIVE before beginning DA registration. 12.3. Reliable Unicast to DAs If a DA fails to respond to a unicast UDP message in CONFIG_DA_RETRY seconds, the message should be retried. If a DA fails to respond after CONFIG_DA_MAX seconds, the SA should consider the DA to have gone down. The UA should use a different DA. If no such DA responds, DA discovery should be used to find a new DA. If no DA is available, multicast is used. 12.4. DA Scope Configuration By default, DAs are configured with the "DEFAULT" scope. Administrators may add other configured scopes, in order to support UAs and SAs in non default scopes. The default configuration MUST NOT be removed from the DA unless: - There are other DAs which support the "DEFAULT" scope, or - All UAs and SAs have been configured with non-default scopes. Non-default scopes can be phased-in as the SLP deployment grows. Default scopes should be phased out only when the non-default scopes are universally configured. If a DA and SA are coresident on a host (quite possibly implemented by the same process), configuration of the host is considerably simplified if the SA supports only scopes also supported by the DA. That is, the SA SHOULD NOT advertise services in any scopes which are not supported by the coresident DA. This means that incoming requests Guttman,Perkins,Veizades,Day Expires 30 January 1999 [Page 37]
Internet Draft Service Location Protocol, Version 2 30 July 1998 can be answered by a single data store; the SA and DA registrations do not need to be kept separately. 12.5. DAs and Authentication Blocks DAs are not configured with protected scope private keys. This means they will not be able to sign URLs and <attr-list>s, but only cache them for SAs, forwarding them to UAs. Consequently, in a protected scope the DA will not accept: SrvReg without the FRESH flag set or AttrRqst or SrvDeReg with a <tag-list> included. In these cases an AUTHENTICATION_FAILED error is returned. 13. SLP Protocol Extensions 13.1. Required Attribute Missing Option 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 Type = 0x0001 | Extension Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Template IDVer Length | Template IDVer String \ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |Required Attr <tag-list> Length| Required Attr <tag-list> \ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Required attributes and the format of the IDVer string are defined by [15]. If a SA or DA receives a SrvRqst or a SrvReg which fails to include a Required Attribute for the requested Service Type (according to the service template), it MAY return the Required Attribute Extension in addition to the reply corresponding to the message. The sender SHOULD reissue the message with a search filter including the attributes listed in the returned Required Attribute Extension. Similarly, the Required Attribute Extension may be returned in response to a SrvDereg message that contains a required attribute tag. The Template IDVer String is the name and version number string of the service template which defines the given attribute as required. It SHOULD be included, but can be omitted if a given SA or DA has been individually configured to have 'required attributes.' The Required Attribute <tag-list> MUST NOT include wild cards. Guttman,Perkins,Veizades,Day Expires 30 January 1999 [Page 38]
Internet Draft Service Location Protocol, Version 2 30 July 1998 13.2. Cryptographic Request Option If a UA wishes to obtain an Authentication Block using a non-default algorithm (i.e., not using DSA), it SHOULD include a SLP Extension requesting a particular BSD and optionally a Key Generation Number. 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 Type = 0x0002 | Extension Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Desired BSD |Key Generation Number(optional)| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-------------------------------+ The Desired BSD (see Section 9.1) is a two byte value. If the DA or SA does not support this OPTIONAL extension, it will ignore it and return a DSA authentication block. If it supports the Extension and the algorithm identified by the Desired BSD it will return an Authentication block using the desired algorithm. If a Key Generation Number is included, the host receiving the request MUST reply with an Authentication Block which uses the key with the requested Key Generation Number (see Section 9.2). To omit a Key Generation Number in the Cryptographic Request Option, the Key Generation Number field is set to 0. If the SA or DA supports this option and receives a multicast request for a Key Generation Number or a cryptographic algorithm it does not support, it returns an AUTHENTICATION_UNKNOWN error. Guttman,Perkins,Veizades,Day Expires 30 January 1999 [Page 39]
Internet Draft Service Location Protocol, Version 2 30 July 1998 14. Protocol Timing Defaults Interval name Section Default Value Meaning ------------------- ------- ------------- ------------------------ CONFIG_MC_RETRY 6.3 each second, Retry multicast query backing off until no new values gradually arrive. CONFIG_MC_MAX 6.3 15 seconds Max time to wait for a complete multicast query response (all values.) CONFIG_START_WAIT 12.2.1 3 seconds Wait to perform DA discovery on reboot. CONFIG_DA_RETRY 12.3 2 seconds Retransmit DA discovery, try it 3 times. CONFIG_DA_MAX 12.3 6 seconds Give up on requests sent to a DA. CONFIG_DA_BEAT 12.2.2 3 hours DA Heartbeat, so that SAs passively detect new DAs. CONFIG_DA_FIND 12.3 900 seconds Minimum interval to wait before repeating Active DA discovery. CONFIG_REG_PASSIVE 12.2 1-3 seconds Wait to register services on passive DA discovery. CONFIG_REG_ACTIVE 8.3 1-3 seconds Wait to register services on active DA discovery. CONFIG_CLOSE_CONN 6.2 5 minutes DAs and SAs close idle connections. 15. Optional Configuration Broadcast Only Any SLP agent SHOULD be configurable to use broadcast only. See Sections 6.1 and 12.2. Predefined DA A UA or SA SHOULD be configurable to use a predefined DA. No DA Discovery The UA or SA SHOULD be configurable to ONLY use predefined and DHCP-configured DAs and perform no active or passive DA discovery. Multicast TTL The default multicast TTL is 32. Agents SHOULD be configurable to use other values. A lower value will focus the multicast convergence algorithm on smaller Guttman,Perkins,Veizades,Day Expires 30 January 1999 [Page 40]
Internet Draft Service Location Protocol, Version 2 30 July 1998 subnetworks, decreasing the number of responses and increases the performance of service location. This may result in UAs obtaining different results for the identical requests depending on where they are connected to the network. Timing Values Time values other than the default MAY be configurable. See Section 14. Scopes A UA MAY be configurable to support User Selectable scopes by omitting all predefined scopes. See Section 11.2. A UA or SA MUST be configurable to use specific scopes by default. Additionally, a UA or SA MUST be configurable to use specific scopes for requests for and registrations of specific service types. The scope or scopes of a DA MUST be configurable. The default value for a DA is to have the scope "DEFAULT" if not otherwise configured. DHCP Configuration DHCP options 78 and 79 may be used to configure SLP. If DA locations are configured using DHCP, these SHOULD be used in preference to DAs discovered actively or passively. One or more of the scopes configured using DHCP MUST be used in requests. The entire configured <scope-list> MUST be used in registration and DA configuration messages. Service Template UAs and SAs MAY be configured by using Service Templates. Besides simplifying the specification of attribute values, this also allows them to enforce the inclusion of 'required' attributes in SrvRqst, SrvReg and SrvDeReg messages. DAs MAY be configured with templates to allow them to WARN UAs and SAs in these cases. See Section 10.4. 16. IANA Considerations Further Block Structured Descriptor (BSD) values may be standardized in the future by submitting a document which describes: - The data format of the Structured Authenticator block. - Which cryptographic algorithm to use (including a reference to a technical specification of the algorithm.) Guttman,Perkins,Veizades,Day Expires 30 January 1999 [Page 41]
Internet Draft Service Location Protocol, Version 2 30 July 1998 - The format of any keying material required for preconfiguring UAs, DAs and SAs. Also include any considerations regarding key distribution. - Security considerations to alert others to the strengths and weaknesses of the approach. The IANA will assign BSD numbers (from the range 0x0003 to 0x7FFF) on a first come, first served basis. New function-IDs, in the range 12-255, may be standardized by the method of IETF Consensus [20]. Similarly, new extensions with types in the range 3-65535 may be standardized by the method of IETF Consensus. Specification and Expert Review is required for the assignment of new error numbers in the range of 15-65535. Protocol elements used with Service Location Protocol may also require IANA registration actions. SLP is used in conjunction with "service:" URLs and service templates [15]. These are standardized by the method of a Designated Expert and a mailing list (see [15].) 17. Internationalization Considerations SLP messages support the use of multiple languages by providing a Language Tag field in the common message header (see Section 8). Services MAY be registered in multiple languages. This provides attributes so that users with different language skills may select services interactively. A service which is registered in multiple languages may be queried in multiple languages. The language of the SrvRqst or AttrRqst is used to satisfy the request. If the requested language is not supported, a LANGUAGE_NOT_SUPPORTED error is returned. SrvRply and AttrRply messages are always in the same language of the request. A DA or SA MAY be configured with translations of Service Templates [15] for the same service type. This will allow the DA or SA to translate a request (say in Italian) to the language of the service advertisement (say in English) and then translate the reply back to Italian. Similarly, a UA MAY use templates to translate outgoing requests and incoming replies. The dialect field in the Language Tag MAY be used: Requests which can be fulfilled by matching a language and dialect will be preferred to those which match only the language portion. Otherwise, dialects have no effect on matching requests. Guttman,Perkins,Veizades,Day Expires 30 January 1999 [Page 42]
Internet Draft Service Location Protocol, Version 2 30 July 1998 18. Security Considerations SLP provides for authentication of service URLs and service attributes. This provides UAs and DAs with knowledge of the integrity of service URLs and attributes included in SLP messages. The only systems which can generate digital signatures are those which have been configured by administrators in advance. Agents which verify signed data may assume it is 'trustworthy' inasmuch as administrators have ensured the cryptographic keying of SAs and DAs reflects 'trustworthiness.' Service Location does not provide confidentiality. Because the objective of this protocol is to advertise services to a community of users, confidentiality might not generally be needed when this protocol is used in non-sensitive environments. Specialized schemes might be able to provide confidentiality, if needed in the future. Sites requiring confidentiality should implement the IP Encapsulating Security Payload (ESP) [3] to provide confidentiality for Service Location messages. Using unprotected scopes, an adversary might easily use this protocol to advertise services on servers controlled by the adversary and thereby gain access to users' private information. Further, an adversary using this protocol will find it much easier to engage in selective denial of service attacks. Sites that are in potentially hostile environments (e.g., are directly connected to the Internet) should consider the advantages of distributing keys associated with protected scopes prior to deploying the sensitive directory agents or service agents. Service Location is useful as a bootstrap protocol. It may be used in environments in which no preconfiguration is possible. In such situations, a certain amount of "blind faith" is required: Without any prior configuration it is impossible to use any of the security mechanisms described above. Service Location will make use of the mechanisms provided by the Security Area of the IETF for key distribution as they become available. At this point it would only be possible to gain the benefits associated with the use of protected scopes if some cryptographic information can be preconfigured with the end systems before they use Service Location. 19. Acknowledgments This document incorporates ideas from work on several discovery protocols, including RDP by Perkins and Harjono, and PDS by Michael Day. John Veizades was working group chair for much of the development of Service Location Protocol, instrumental in its standardization, and the lead author of SLPv1 [24]. Guttman,Perkins,Veizades,Day Expires 30 January 1999 [Page 43]
Internet Draft Service Location Protocol, Version 2 30 July 1998 20. Full Copyright Statement Copyright (C) The Internet Society (1997). 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." References [1] Port numbers, July 1997. ftp://ftp.isi.edu/in-notes/iana/assignments/port-numbers. [2] ISO/IEC JTC1/SC 21. Certificate Extensions. Draft Amendment DAM 4 to ISO/IEC 9594-2, December 1996. [3] ISO/IEC JTC1/SC 21. Certificate Extensions. Draft Amendment DAM 2 to ISO/IEC 9594-6, December 1996. [4] ISO/IEC JTC1/SC 21. Certificate Extensions. Draft Amendment DAM 1 to ISO/IEC 9594-7, December 1996. [5] ISO/IEC JTC1/SC 21. Certificate Extensions. Draft Amendment DAM 1 to ISO/IEC 9594-8, December 1996. [6] Unicode Technical Report #4. The unicode standard, version 2.0. Technical Report ISBN 0-201-48345-9, The Unicode Consortium, 1996. Guttman,Perkins,Veizades,Day Expires 30 January 1999 [Page 44]
Internet Draft Service Location Protocol, Version 2 30 July 1998 [7] H. Alvestrand. Tags for the Identification of Languages. RFC 1766, March 1995. [8] D. Balenson. Privacy Enhancement for Internet Electronic Mail: Part III: Algorithms, Modes, and Identifiers. RFC 1423, February 1993. [9] T. Berners-Lee, L. Masinter, and M. McCahill. Uniform Resource Locators (URL). RFC 1738, December 1994. [10] S. Bradner. Key Words for Use in RFCs to Indicate Requirement Levels. RFC 2119, March 1997. [11] CCITT. Specification of the Abstract Syntax Notation One (ASN.1). Recommendation X.208, 1988. [12] CCITT. The Directory Authentication Framework. Recommendation X.509, 1988. [13] D. Crocker and P. Overell. Augmented BNF for Syntax Specifications: ABNF. RFC 2234, November 1997. [14] S. Gursharan, R. Andrews, and A. Oppenheimer. Inside AppleTalk. Addison-Wesley, 1990. [15] E. Guttman, C. Perkins, and J. Kempf. Service Templates and service: Schemes. draft-ietf-svrloc-service-scheme-05.txt, November 1997. (work in progress). [16] T. Howes. The string representation of LDAP search filters. draft-ietf-asid-ldapv3-filter-03.txt, October 1997. (work in progress). [17] H. Krawczyk, M. Bellare, and R. Cannetti. HMAC: Keyed-Hashing for Message Authentication. RFC 2104, February 1997. [18] D. Meyer. Administratively Scoped IP Multicast. RFC 2365, July 1998. [19] David L. Mills. Network Time Protocol (Version 3): Specification, Implementation and Analysis. RFC 1305, March 1992. [20] Thomas Narten and Harald Tveit Alvestrand. Guidelines for Writing an IANA Considerations Section in RFCs. draft-iesg-iana-considerations-04.txt, May 1998. (work in progress). Guttman,Perkins,Veizades,Day Expires 30 January 1999 [Page 45]
Internet Draft Service Location Protocol, Version 2 30 July 1998 [21] Microsoft Networks. SMB File Sharing Protocol Extensions 3.0, Document Version 1.09, November 1989. [22] National Institute of Standards and Technology. Digital signature standard. Technical Report NIST FIPS PUB 186, U.S. Department of Commerce, May 1994. [23] Ronald L. Rivest. The MD5 Message-Digest Algorithm. RFC 1321, April 1992. [24] J. Veizades, E. Guttman, C. Perkins, and S. Kaplan. Service Location Protocol. RFC 2165, July 1997. [25] F. Yergeau. UTF-8, a transformation format of ISO 10646. RFC 2279, January 1998. Authors' Addresses Erik Guttman Charles Perkins Sun Microsystems Sun Microsystems Bahnstr. 2 901 San Antonio Road 74915 Waibstadt Palo Alto, CA 94040 Germany USA Phone: +49 7263 911 701 +1 650 786 6464 Email: Erik.Guttman@sun.com cperkins@sun.com John Veizades Michael Day @Home Network Intel 385 Ravendale Dr. 734 E. Utah Valley Dr., Ste. 300 Mountain View, CA 94043 American Fork, Utah, 84003 USA USA Phone: +1 650 569 5243 +1 801 763 2341 Email: veizades@home.net Michael_Day@ccm.ut.intel.com Guttman,Perkins,Veizades,Day Expires 30 January 1999 [Page 46]
