One document matched: draft-zhao-slp-remote-da-discovery-04.txt
Differences from draft-zhao-slp-remote-da-discovery-03.txt
INTERNET DRAFT W. Zhao
draft-zhao-slp-remote-da-discovery-04.txt H. Schulzrinne
[Target Category: Standards Track] Columbia University
January 18, 2003 E. Guttman
Expires: July 18, 2003 Sun Microsystems
C. Bisdikian
W. Jerome
IBM
Finding Remote Directory Agents and Service Agents
in the Service Location Protocol via DNS SRV
Status of This Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet- Drafts as reference
material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
Copyright Notice
Copyright (C) The Internet Society (2003). All Rights Reserved.
Abstract
This document describes how to find Directory Agents (DAs) and
Service Agents (SAs) in the Service Location Protocol (SLP) at remote
DNS domains via DNS SRV. It defines the SLP service and the DNS SRV
Resource Record for the SLP service, describes the usage of Gateway
DAs, and gives the steps for a User Agent to discover desired
services in remote DNS domains.
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1. Introduction
The Service Location Protocol (SLP [RFC2608]) is designed for local
service discovery within one administrative domain. To extend SLP for
discovering non-local services in remote DNS domains, a key issue is
to enable a User Agent (UA) to find remote accessible Directory
Agents (DAs) and Service Agents (SAs) in given DNS domains without
relying on multicast. This document describes using DNS SRV [RFC2782]
for this purpose.
The SLP service has a service type of "service:slp" (defined in
Section 2), and is provided by DAs and SAs. For a domain, the SLP
servers listed as DNS SRV Resource Records (RRs) need to be
functionally equivalent so that a UA can use any server in the list
to get the same service information. However, two SLP servers will be
different if at least one is SA, or they are in different scopes. In
other words, only DAs in the same scope are functionally equivalent.
Thus, if all remote accessible SLP servers in a domain are DAs in the
same scope, then the domain just lists these DAs as DNS SRV RRs,
otherwise the domain needs to deploy Gateway DAs (defined in Section
4), and list those Gateway DAs as DNS SRV RRs.
This document defines the "service:slp" template and the DNS SRV RR
for the SLP service, describes the usage of Gateway DAs, and gives
the steps for a UA to discover desired services in remote DNS
domains.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted according to RFC 2119 [RFC2119].
2. The "service:slp" Template
The "service:slp" template defines the attributes associated with the
SLP service. Please refer to RFC 2609 [RFC2609] for detailed
explanation of the syntax.
Name of submitters: Weibin Zhao <zwb@cs.columbia.edu>
Henning Schulzrinne <hgs@cs.columbia.edu>
Language of service template: en (English)
Security Considerations:
Standard SLP authentication SHOULD be used to protect valuable
SLP server and scope information.
Template Text:
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----------------------template begins here-----------------------
template-type = slp
template-version = 1.0
template-description =
This template is designed to enable a UA to discover information
(including URL, server-type and scope) about all remote accessible
DAs and SAs in a domain by unicasting a Service Request (SrvRqst)
with "service:slp" as service type to a Gateway DA.
template-url-syntax =
; No additional URL information is required. An example service
; URL for the SLP service is: service:slp://myda.mydomain:427
slp-server-type = STRING L
DA
# The type of the server that provides the SLP service
DA,SA
slp-scope = STRING M L
# The serving scopes of this server
-----------------------template ends here------------------------
3. The DNS SRV RR for the SLP service
The name of the DNS SRV RR for the SLP service has the following
format:
_slp._<protocol>.<domain>
where <protocol> is either "tcp" or "udp", and <domain> is a domain
name (such as example.com). Note that "slp" is the symbolic name for
the SLP service in Assigned Numbers [RFC1700], as required by RFC
2782.
For instance, if a UA makes a standard DNS query [RFC1034] for SRV
RRs of the SLP service using the name:
_slp._tcp.example.com or _slp._udp.example.com
then the UA will receive a list of SRV RRs (which matches the query)
in a DNS reply, such as
_slp._tcp.example.com IN SRV 0 0 427 da1.example.com
_slp._tcp.example.com IN SRV 0 0 427 da2.example.com
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or
_slp._udp.example.com IN SRV 0 0 427 da1.example.com
_slp._udp.example.com IN SRV 0 0 427 da2.example.com
4. Gateway DA
A Gateway DA (GDA) carries the "slp-gateway" attribute keyword in its
DAAdvert, and maintains information (including URL, server-type and
scope, as defined in the "service:slp" template) about all remote
accessible DAs and SAs in its domain.
By default, a GDA SHOULD be statically configured only since the
administrator normally needs to decide which DAs and SAs should be
accessible from remote UAs. The administrator can manually configure
a GDA using serialized registration files, and update "service:slp"
registrations at a GDA using SrvReg and SrvDeReg messages.
Note that a GDA MAY be configured to periodically perform active DA
and SA discovery by multicasting "service:directory-agent" and
"service:service-agent" Service Requests (SrvRqsts) to gather
information about DAs and SAs in its domain. However, this feature
MUST be used with caution because a GDA configured in this way may
expose information about all DAs and SAs in its domain to anyone over
the Internet.
A remote UA can identify a GDA by the "slp-gateway" attribute keyword
in the GDA's DAAdvert, then the UA can unicast a SrvRqst with
"service:slp" as service type and with the Attribute List Extension
[RFC3059] to the GDA to obtain information about all remote
accessible DAs and SAs in the domain. If the UA just wants to
discover DAs (or SAs), it needs to use the predicate "slp-server-
type=DA" (or "slp-server-type=SA") in the SrvRqst message.
5. Steps for Remote Discovery in SLP
Assume that a DNS domain D uses SLP to maintain its service
information, and uses DNS SRV to map its SLP service. The steps for a
remote client C to discover desired services in D are as follows.
(1) C makes a DNS query for SRV RRs of the SLP service in D, and
gets an SLP server list L in a DNS reply.
(2) C selects a server Z from L based on the priority and weight
information per RFC 2782.
(3) C sends a "service:directory-agent" SrvRqst to Z to solicit
Z's DAAdvert.
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If Z's DAAdvert has the "slp-gateway" attribute keyword
then Z is a GDA
C sends a SrvRqst with "service:slp" as service type and
with the Attribute List Extension to Z to obtain information
about all remote accessible DAs and SAs in D.
else Z is a regular DA
(4) After finding out the remote accessible DAs and SAs in D, C can
query these remote DAs or SAs via unicast to discover desired
services in D.
6. Security Considerations
To enable remote discovery in SLP, the local domain information is
exposed to external users. Thus, standard SLP authentication SHOULD
be used to protect valuable service information.
There is a risk that any SA could advertise any service on a
generally accessible DA. Such a DA SHOULD reject all registrations
that cannot be authenticated.
The security considerations for DNS SRV [RFC2782] apply to this
document.
7. Acknowledgments
Kevin Arnold gave good suggestions.
8. Normative References
[RFC2608] E. Guttman, C. Perkins, J. Veizades and M. Day, "Service
location protocol, version 2", RFC 2608, June 1999.
[RFC2782] A. Gulbrandsen, P. Vixie and L. Esibov, "A DNS RR for
specifying the location of services (DNS SRV)", RFC 2782,
February 2000.
[RFC2119] S. Bradner, "Key words for use in RFCs to indicate
requirement levels", BCP 14, RFC 2119, March 1997.
[RFC1700] J. Reynolds and J. Postel, "Assigned Numbers", STD 2,
RFC 1700, October 1994.
[RFC1034] P. Mockapetris, "Domain Names - Concepts and Facilities",
STD 13, RFC 1034, November 1987.
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9. Non-normative References
[RFC2609] E. Guttman, C. Perkins and J. Kempf, "Service Templates
and Service: Schemes", RFC 2609, June, 1999.
[RFC3059] E. Guttman, "Attribute List Extension for the Service
Location Protocol", RFC 3059, February 2001.
10. Authors' Addresses
Weibin Zhao
Department of Computer Science
Columbia University
1214 Amsterdam Avenue, MC 0401
New York, NY 10027-7003
EMail: zwb@cs.columbia.edu
Henning Schulzrinne
Department of Computer Science
Columbia University
1214 Amsterdam Avenue, MC 0401
New York, NY 10027-7003
EMail: hgs@cs.columbia.edu
Erik Guttman
Sun Microsystems
Eichhoelzelstr. 7
74915 Waibstadt
Germany
EMail: Erik.Guttman@sun.com
Chatschik Bisdikian
IBM Corp.
Thomas J. Watson Research Center
19 Skyline Drive
Hawthorne, NY 10532, USA
EMail: bisdik@us.ibm.com
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William F. Jerome
IBM Corp.
Thomas J. Watson Research Center
19 Skyline Drive
Hawthorne, NY 10532, USA
EMail: wfj@us.ibm.com
11. Full Copyright Statement
Copyright (C) The Internet Society (2003). 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.
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