draft-ietf-dnsext-rfc2782bis-00.txt   draft-ietf-dnsext-rfc2782bis-01.txt 
Network Working Group A. Gulbrandsen Network Working Group A. Gulbrandsen
Category: INTERNET-DRAFT Trolltech AS Category: INTERNET-DRAFT Trolltech AS
Obsoletes: 2052 P. Vixie Obsoletes: 2782 P. Vixie
draft-ietf-dnsext-rfc2782bis-00.txt Internet Software Consortium draft-ietf-dnsext-rfc2782bis-01.txt Internet Software Consortium
November 16, 2000 L. Esibov June 6, 2001 L. Esibov
Expires: May 16, 2001 Microsoft Corp. Expires: December 6, 2001 Microsoft Corp.
A DNS RR for specifying the location of services (DNS SRV) A DNS RR for specifying the location of services (DNS SRV)
Status of this Memo Status of this Memo
This document is an Internet-Draft and is in full conformance with all This document is an Internet-Draft and is in full conformance with all
provisions of Section 10 of RFC2026. provisions of Section 10 of RFC2026.
Internet-Drafts are working documents of the Internet Engineering Task Internet-Drafts are working documents of the Internet Engineering Task
Force (IETF), its areas, and its working groups. Note that other groups Force (IETF), its areas, and its working groups. Note that other groups
may also distribute working documents as Internet- Drafts. may also distribute working documents as Internet- Drafts.
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or to cite them other than as "work in progress." or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt http://www.ietf.org/ietf/1id-abstracts.txt
The list of Internet-Draft Shadow Directories can be accessed at The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html. http://www.ietf.org/shadow.html.
Copyright Notice Copyright Notice
Copyright (C) The Internet Society (2000). All Rights Reserved. Copyright (C) The Internet Society (2001). All Rights Reserved.
Abstract Abstract
This document describes a DNS RR which specifies the location of the This document describes a DNS RR which specifies the location of the
server(s) for a specific protocol and domain. server(s) for a specific protocol and domain.
Overview and rationale Overview and rationale
Currently, one must either know the exact address of a server to Currently, one must either know the exact address of a server to
contact it, or broadcast a question. contact it, or broadcast a question.
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servers and connect to the preferred one: servers and connect to the preferred one:
Do a lookup for QNAME=_service._protocol.domain, QCLASS=IN, Do a lookup for QNAME=_service._protocol.domain, QCLASS=IN,
QTYPE=SRV. QTYPE=SRV.
If the reply is NOERROR, ANCOUNT>0 and there is at least one If the reply is NOERROR, ANCOUNT>0 and there is at least one
SRV RR which specifies the requested Service and Protocol in SRV RR which specifies the requested Service and Protocol in
the reply: the reply:
If there is precisely one SRV RR, and its Target is "." If there is precisely one SRV RR, and its Target is "."
(the root domain), abort. (the root domain), abort and do not attempt lookup for
QNAME=domain, QCLASS=IN, QTYPE=A.
Else, for all such RR's, build a list of (Priority, Weight, Else, for all such RR's, build a list of (Priority, Weight,
Target) tuples Target) tuples
Sort the list by priority (lowest number first) Sort the list by priority (lowest number first)
Create a new empty list Create a new empty list
For each distinct priority level For each distinct priority level
While there are still elements left at this priority While there are still elements left at this priority
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"ns1.ip-provider.net." and "ns2" - again, "ip-provider.net." is "ns1.ip-provider.net." and "ns2" - again, "ip-provider.net." is
quoted and only needs to be counted once. quoted and only needs to be counted once.
120 bytes for the 6 address records (assuming IPv4 only) mentioned 120 bytes for the 6 address records (assuming IPv4 only) mentioned
by the SRV and NS RR's. by the SRV and NS RR's.
IANA Considerations IANA Considerations
The IANA has assigned RR type value 33 to the SRV RR. No other IANA The IANA has assigned RR type value 33 to the SRV RR. No other IANA
services are required by this document. services are required by this document.
Changes from RFC 2052 Changes from RFC 2782
This document obsoletes RFC 2052. The major change from that This document obsoletes RFC 2782
previous, experimental, version of this specification is that now the Only editorial clarifications were made to this document. Namely
protocol and service labels are prepended with an underscore, to
lower the probability of an accidental clash with a similar name used - it was clarified that "Weight" subsection refers to real "random
for unrelated purposes. Aside from that, changes are only intended number" rather than integer number;
to increase the clarity and completeness of the document. This
document especially clarifies the use of the Weight field of the SRV - it was clarified that the "Name" used in the owner name of the SRV
records. record used in "The format of the SRV RR" section is a "Domain"
name;
- the "QNAME=_service._protocol.target" was replaced by
"QNAME=_service._protocol.domain" in "Usage rules" section to
eliminate a possibility of confusion with the Target field of the
SRV record.
- client's behavior when response to a query contains a single SRV
RR and its Target is "." is clarified in "Usage rules" section.
Security Considerations Security Considerations
The authors believe this RR to not cause any new security problems. The authors believe this RR to not cause any new security problems.
Some problems become more visible, though. Some problems become more visible, though.
- The ability to specify ports on a fine-grained basis obviously - The ability to specify ports on a fine-grained basis obviously
changes how a router can filter packets. It becomes impossible changes how a router can filter packets. It becomes impossible
to block internal clients from accessing specific external to block internal clients from accessing specific external
services, slightly harder to block internal users from running services, slightly harder to block internal users from running
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Levon Esibov Levon Esibov
Microsoft Corporation Microsoft Corporation
One Microsoft Way One Microsoft Way
Redmond, WA 98052 Redmond, WA 98052
EMail: levone@microsoft.com EMail: levone@microsoft.com
Full Copyright Statement Full Copyright Statement
Copyright (C) The Internet Society (2000). All Rights Reserved. Copyright (C) The Internet Society (2001). All Rights Reserved.
This document and translations of it may be copied and furnished to This document and translations of it may be copied and furnished to
others, and derivative works that comment on or otherwise explain it others, and derivative works that comment on or otherwise explain it
or assist in its implementation may be prepared, copied, published or assist in its implementation may be prepared, copied, published
and distributed, in whole or in part, without restriction of any and distributed, in whole or in part, without restriction of any
kind, provided that the above copyright notice and this paragraph are kind, provided that the above copyright notice and this paragraph are
included on all such copies and derivative works. However, this included on all such copies and derivative works. However, this
document itself may not be modified in any way, such as by removing document itself may not be modified in any way, such as by removing
the copyright notice or references to the Internet Society or other the copyright notice or references to the Internet Society or other
Internet organizations, except as needed for the purpose of Internet organizations, except as needed for the purpose of
 End of changes. 

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