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doc/draft/draft-ietf-dnsext-ad-is-secure-00.txt
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doc/draft/draft-ietf-dnsext-ad-is-secure-00.txt
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DNSEXT Working Group Brian Wellington (Nominum)
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INTERNET-DRAFT Olafur Gudmundsson (NAI Labs)
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<draft-ietf-dnsext-ad-is-secure-00.txt> November 2000
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Updates: RFC 2535
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Redefinition of DNS AD bit
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Status of this Memo
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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
|
||||
|
||||
Comments should be sent to the authors or the DNSEXT WG mailing list
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||||
namedroppers@ops.ietf.org
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||||
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This draft expires on May 17, 2001.
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Copyright Notice
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Copyright (C) The Internet Society (2000). All rights reserved.
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Abstract
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Based on implementation experience, the current definition of the AD
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bit in the DNS header is not useful. This draft changes the
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specification so that the AD bit is only set on answers where
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signatures have been cryptographically verified.
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Expires May 2001 [Page 1]
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INTERNET-DRAFT AD bit set on secure answers November 2000
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1 - Introduction
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Familiarity with the DNS system [RFC1034, RFC1035] and DNS security
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extensions [RFC2535] is helpful but not necessary.
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As specified in RFC 2535 (section 6.1), the AD bit indicates in a
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response that all the data included in the answer and authority
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portion of the response has been authenticated by the server
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according to the policies of that server. This is not especially
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useful in practice, since a conformant server should never reply with
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data that failed its security policy.
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This draft proposes to redefine the AD bit such that it is only set
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if all data in the response has been cryptographically verified.
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Thus, a response containing properly delegated insecure data will not
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have AD set, as will a response from a server configured without
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DNSSEC keys. As before, data which failed to verify will not be
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returned. An application can then use the value of the AD bit to
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determine if the data is secure or not.
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1.1 - Requirements
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The key words "MUST NOT", "SHOULD", "SHOULD NOT", and "MAY" in this
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document are to be interpreted as described in RFC2119.
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1.2 - Updated documents and sections
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The definition of the AD bit in RFC2535, Section 6.1, is changed.
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2 - Setting of AD bit
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Section 6.1 of RFC2535 says:
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"The AD bit MUST NOT be set on a response unless all of the RRs in
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the answer and authority sections of the response are either
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Authenticated or Insecure."
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The changes are to delete the words "either" and "or Insecure" from
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the sentence.
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The replacement text reads:
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"The AD bit MUST NOT be set on a response unless all of the RRsets in
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the answer and authority sections of the response are Authenticated."
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Expires May 2001 [Page 2]
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INTERNET-DRAFT AD bit set on secure answers November 2000
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If the answer section contains any data, the server MUST NOT include
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data in the authority section that would cause the AD bit to be
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unset.
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The AD bit MUST NOT be set on a response unless all of the RRsets in
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the answer and authority sections are Authenticated.
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A resolver MUST NOT blindly trust the AD bit unless it communicates
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with the server over secure transport mechanism or using message
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authentication such as TSIG[RFC2845] or SIG(0)[RFC2931], and the
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resolver policy is that it can trust the server.
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A DNS server following this modified specification will only set the
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AD bit when it has verified the data in the answer. In the case of a
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primary server for a secure zone, the data MAY be considered
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Authenticated, depending on local policy. Secondary servers SHOULD
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NOT consider data Authenticated unless the zone was transfered
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securely or the data was verified.
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3 - Interpretation of the AD bit
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A response containing data marked Insecure in the answer or authority
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section will never have the AD bit set. In this case, the resolver
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SHOULD treat the data as Insecure whether or not SIG records are
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present.
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4 - Security Considerations:
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This document redefines a bit in the DNS header. If a resolver
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trusts the value of the AD bit, it must be sure that the server is
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using the updated definition.
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5 - IANA Considerations:
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None
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6 - Acknowledgments:
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The following people have provided input on this document: Andreas
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Gustafsson, Bob Halley, Steven Jacob,
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References:
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[RFC1035] P. Mockapetris, ``Domain Names - Implementation and
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Specification'', STD 13, RFC 1035, November 1987.
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[RFC2535] D. Eastlake, ``Domain Name System Security Extensions'', RFC
|
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2535, March 1999.
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|
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Expires May 2001 [Page 3]
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INTERNET-DRAFT AD bit set on secure answers November 2000
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|
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[RFC2845] P. Vixie, O. Gudmundsson, D. Eastlake, B. Wellington,
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``Secret Key Transaction Authentication for DNS (TSIG)'', RFC
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2845, May 2000.
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[RFC2931] D. Eastlake, ``DNS Request and Transaction Signatures
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(SIG(0))'', RFC 2931, September 2000.
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Authors Addresses
|
||||
|
||||
Brian Wellington Olafur Gudmundsson
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Nominum Inc. NAI Labs
|
||||
950 Charter Street 3060 Washington Road (Rt. 97)
|
||||
Redwood City, CA, 94063 Glenwood, MD, 21738
|
||||
USA USA
|
||||
+1 650 381 6022 +1 443 259 2389
|
||||
<Brian.Wellington@nominum.com> <ogud@tislabs.com>
|
||||
|
||||
|
||||
Full Copyright Statement
|
||||
|
||||
Copyright (C) The Internet Society (2000). 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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||||
|
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Expires May 2001 [Page 4]
|
682
doc/draft/draft-ietf-dnsext-rfc2782bis-00.txt
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682
doc/draft/draft-ietf-dnsext-rfc2782bis-00.txt
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@ -0,0 +1,682 @@
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||||
|
||||
|
||||
|
||||
|
||||
Network Working Group A. Gulbrandsen
|
||||
Category: INTERNET-DRAFT Trolltech AS
|
||||
Obsoletes: 2052 P. Vixie
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||||
draft-ietf-dnsext-rfc2782bis-00.txt Internet Software Consortium
|
||||
November 16, 2000 L. Esibov
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||||
Expires: May 16, 2001 Microsoft Corp.
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||||
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|
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A DNS RR for specifying the location of services (DNS SRV)
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|
||||
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 (2000). All Rights Reserved.
|
||||
|
||||
Abstract
|
||||
|
||||
This document describes a DNS RR which specifies the location of the
|
||||
server(s) for a specific protocol and domain.
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||||
|
||||
Overview and rationale
|
||||
|
||||
Currently, one must either know the exact address of a server to
|
||||
contact it, or broadcast a question.
|
||||
|
||||
The SRV RR allows administrators to use several servers for a single
|
||||
domain, to move services from host to host with little fuss, and to
|
||||
designate some hosts as primary servers for a service and others as
|
||||
backups.
|
||||
|
||||
Clients ask for a specific service/protocol for a specific domain
|
||||
(the word domain is used here in the strict RFC 1034 sense), and get
|
||||
back the names of any available servers.
|
||||
|
||||
Note that where this document refers to "address records", it means A
|
||||
RR's, AAAA RR's, or their most modern equivalent.
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Expires May 2001 [Page 1]
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|
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INTERNET-DRAFT DNS SRV RR Novemeber 2000
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Definitions
|
||||
|
||||
The key words "MUST", "MUST NOT", "SHOULD", "SHOULD NOT" and "MAY"
|
||||
used in this document are to be interpreted as specified in [BCP 14].
|
||||
Other terms used in this document are defined in the DNS
|
||||
specification, RFC 1034.
|
||||
|
||||
Applicability Statement
|
||||
|
||||
In general, it is expected that SRV records will be used by clients
|
||||
for applications where the relevant protocol specification indicates
|
||||
that clients should use the SRV record. Such specification MUST
|
||||
define the symbolic name to be used in the Service field of the SRV
|
||||
record as described below. It also MUST include security
|
||||
considerations. Service SRV records SHOULD NOT be used in the absence
|
||||
of such specification.
|
||||
|
||||
Introductory example
|
||||
|
||||
If a SRV-cognizant LDAP client wants to discover a LDAP server that
|
||||
supports TCP protocol and provides LDAP service for the domain
|
||||
example.com., it does a lookup of
|
||||
|
||||
_ldap._tcp.example.com
|
||||
|
||||
as described in [ARM]. The example zone file near the end of this
|
||||
memo contains answering RRs for an SRV query.
|
||||
|
||||
Note: LDAP is chosen as an example for illustrative purposes only,
|
||||
and the LDAP examples used in this document should not be considered
|
||||
a definitive statement on the recommended way for LDAP to use SRV
|
||||
records. As described in the earlier applicability section, consult
|
||||
the appropriate LDAP documents for the recommended procedures.
|
||||
|
||||
The format of the SRV RR
|
||||
|
||||
Here is the format of the SRV RR, whose DNS type code is 33:
|
||||
|
||||
_Service._Proto.Domain TTL Class SRV Priority Weight Port Target
|
||||
|
||||
(There is an example near the end of this document.)
|
||||
|
||||
Service
|
||||
The symbolic name of the desired service, as defined in Assigned
|
||||
Numbers [STD 2] or locally. An underscore (_) is prepended to
|
||||
the service identifier to avoid collisions with DNS labels that
|
||||
occur in nature.
|
||||
|
||||
|
||||
|
||||
|
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|
||||
Expires May 2001 [Page 2]
|
||||
|
||||
INTERNET-DRAFT DNS SRV RR Novemeber 2000
|
||||
|
||||
|
||||
Some widely used services, notably POP, don't have a single
|
||||
universal name. If Assigned Numbers names the service
|
||||
indicated, that name is the only name which is legal for SRV
|
||||
lookups. The Service is case insensitive.
|
||||
|
||||
Proto
|
||||
The symbolic name of the desired protocol, with an underscore
|
||||
(_) prepended to prevent collisions with DNS labels that occur
|
||||
in nature. _TCP and _UDP are at present the most useful values
|
||||
for this field, though any name defined by Assigned Numbers or
|
||||
locally may be used (as for Service). The Proto is case
|
||||
insensitive.
|
||||
|
||||
Domain
|
||||
The domain this RR refers to. The SRV RR is unique in that the
|
||||
name one searches for is not this Domain name; the example near
|
||||
the end shows this clearly.
|
||||
|
||||
TTL
|
||||
Standard DNS meaning [RFC 1035].
|
||||
|
||||
Class
|
||||
Standard DNS meaning [RFC 1035]. SRV records occur in the IN
|
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Class.
|
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|
||||
Priority
|
||||
The priority of this target host. A client MUST attempt to
|
||||
contact the target host with the lowest-numbered priority it can
|
||||
reach; target hosts with the same priority SHOULD be tried in an
|
||||
order defined by the weight field. The range is 0-65535. This
|
||||
is a 16 bit unsigned integer in network byte order.
|
||||
|
||||
Weight
|
||||
A server selection mechanism. The weight field specifies a
|
||||
relative weight for entries with the same priority. Larger
|
||||
weights SHOULD be given a proportionately higher probability of
|
||||
being selected. The range of this number is 0-65535. This is a
|
||||
16 bit unsigned integer in network byte order. Domain
|
||||
administrators SHOULD use Weight 0 when there isn't any server
|
||||
selection to do, to make the RR easier to read for humans (less
|
||||
noisy). In the presence of records containing weights greater
|
||||
than 0, records with weight 0 should have a very small chance of
|
||||
being selected.
|
||||
|
||||
In the absence of a protocol whose specification calls for the
|
||||
use of other weighting information, a client arranges the SRV
|
||||
RRs of the same Priority in the order in which target hosts,
|
||||
|
||||
|
||||
|
||||
|
||||
Expires May 2001 [Page 3]
|
||||
|
||||
INTERNET-DRAFT DNS SRV RR Novemeber 2000
|
||||
|
||||
|
||||
specified by the SRV RRs, will be contacted. The following
|
||||
algorithm SHOULD be used to order the SRV RRs of the same
|
||||
priority:
|
||||
|
||||
To select a target to be contacted next, arrange all SRV RRs
|
||||
(that have not been ordered yet) in any order, except that all
|
||||
those with weight 0 are placed at the beginning of the list.
|
||||
|
||||
Compute the sum of the weights of those RRs, and with each RR
|
||||
associate the running sum in the selected order. Then choose a
|
||||
uniform random real number between 0 and the sum computed
|
||||
(inclusive), and select the RR whose running sum value is the
|
||||
first in the selected order which is greater than or equal to
|
||||
the random number selected. The target host specified in the
|
||||
selected SRV RR is the next one to be contacted by the client.
|
||||
Remove this SRV RR from the set of the unordered SRV RRs and
|
||||
apply the described algorithm to the unordered SRV RRs to select
|
||||
the next target host. Continue the ordering process until there
|
||||
are no unordered SRV RRs. This process is repeated for each
|
||||
Priority.
|
||||
|
||||
Port
|
||||
The port on this target host of this service. The range is 0-
|
||||
65535. This is a 16 bit unsigned integer in network byte order.
|
||||
This is often as specified in Assigned Numbers but need not be.
|
||||
|
||||
Target
|
||||
The domain name of the target host. There MUST be one or more
|
||||
address records for this name, the name MUST NOT be an alias (in
|
||||
the sense of RFC 1034 or RFC 2181). Implementors are urged, but
|
||||
not required, to return the address record(s) in the Additional
|
||||
Data section. Unless and until permitted by future standards
|
||||
action, name compression is not to be used for this field.
|
||||
|
||||
A Target of "." means that the service is decidedly not
|
||||
available at this domain.
|
||||
|
||||
Domain administrator advice
|
||||
|
||||
Expecting everyone to update their client applications when the first
|
||||
server publishes a SRV RR is futile (even if desirable). Therefore
|
||||
SRV would have to coexist with address record lookups for existing
|
||||
protocols, and DNS administrators should try to provide address
|
||||
records to support old clients:
|
||||
|
||||
- Where the services for a single domain are spread over several
|
||||
hosts, it seems advisable to have a list of address records at
|
||||
the same DNS node as the SRV RR, listing reasonable (if perhaps
|
||||
|
||||
|
||||
|
||||
Expires May 2001 [Page 4]
|
||||
|
||||
INTERNET-DRAFT DNS SRV RR Novemeber 2000
|
||||
|
||||
|
||||
suboptimal) fallback hosts for Telnet, NNTP and other protocols
|
||||
likely to be used with this name. Note that some programs only
|
||||
try the first address they get back from e.g. gethostbyname(),
|
||||
and we don't know how widespread this behavior is.
|
||||
|
||||
- Where one service is provided by several hosts, one can either
|
||||
provide address records for all the hosts (in which case the
|
||||
round-robin mechanism, where available, will share the load
|
||||
equally) or just for one (presumably the fastest).
|
||||
|
||||
- If a host is intended to provide a service only when the main
|
||||
server(s) is/are down, it probably shouldn't be listed in
|
||||
address records.
|
||||
|
||||
- Hosts that are referenced by backup address records must use the
|
||||
port number specified in Assigned Numbers for the service.
|
||||
|
||||
- Designers of future protocols for which "secondary servers" is
|
||||
not useful (or meaningful) may choose to not use SRV's support
|
||||
for secondary servers. Clients for such protocols may use or
|
||||
ignore SRV RRs with Priority higher than the RR with the lowest
|
||||
Priority for a domain.
|
||||
|
||||
Currently there's a practical limit of 512 bytes for DNS replies.
|
||||
Until all resolvers can handle larger responses, domain
|
||||
administrators are strongly advised to keep their SRV replies below
|
||||
512 bytes.
|
||||
|
||||
All round numbers, wrote Dr. Johnson, are false, and these numbers
|
||||
are very round: A reply packet has a 30-byte overhead plus the name
|
||||
of the service ("_ldap._tcp.example.com" for instance); each SRV RR
|
||||
adds 20 bytes plus the name of the target host; each NS RR in the NS
|
||||
section is 15 bytes plus the name of the name server host; and
|
||||
finally each A RR in the additional data section is 20 bytes or so,
|
||||
and there are A's for each SRV and NS RR mentioned in the answer.
|
||||
This size estimate is extremely crude, but shouldn't underestimate
|
||||
the actual answer size by much. If an answer may be close to the
|
||||
limit, using a DNS query tool (e.g. "dig") to look at the actual
|
||||
answer is a good idea.
|
||||
|
||||
The "Weight" field
|
||||
|
||||
Weight, the server selection field, is not quite satisfactory, but
|
||||
the actual load on typical servers changes much too quickly to be
|
||||
kept around in DNS caches. It seems to the authors that offering
|
||||
administrators a way to say "this machine is three times as fast as
|
||||
that one" is the best that can practically be done.
|
||||
|
||||
|
||||
|
||||
|
||||
Expires May 2001 [Page 5]
|
||||
|
||||
INTERNET-DRAFT DNS SRV RR Novemeber 2000
|
||||
|
||||
|
||||
The only way the authors can see of getting a "better" load figure is
|
||||
asking a separate server when the client selects a server and
|
||||
contacts it. For short-lived services an extra step in the
|
||||
connection establishment seems too expensive, and for long-lived
|
||||
services, the load figure may well be thrown off a minute after the
|
||||
connection is established when someone else starts or finishes a
|
||||
heavy job.
|
||||
|
||||
Note: There are currently various experiments at providing relative
|
||||
network proximity estimation, available bandwidth estimation, and
|
||||
similar services. Use of the SRV record with such facilities, and in
|
||||
particular the interpretation of the Weight field when these
|
||||
facilities are used, is for further study. Weight is only intended
|
||||
for static, not dynamic, server selection. Using SRV weight for
|
||||
dynamic server selection would require assigning unreasonably short
|
||||
TTLs to the SRV RRs, which would limit the usefulness of the DNS
|
||||
caching mechanism, thus increasing overall network load and
|
||||
decreasing overall reliability. Server selection via SRV is only
|
||||
intended to express static information such as "this server has a
|
||||
faster CPU than that one" or "this server has a much better network
|
||||
connection than that one".
|
||||
|
||||
The Port number
|
||||
|
||||
Currently, the translation from service name to port number happens
|
||||
at the client, often using a file such as /etc/services.
|
||||
|
||||
Moving this information to the DNS makes it less necessary to update
|
||||
these files on every single computer of the net every time a new
|
||||
service is added, and makes it possible to move standard services out
|
||||
of the "root-only" port range on unix.
|
||||
|
||||
Usage rules
|
||||
|
||||
A SRV-cognizant client SHOULD use this procedure to locate a list of
|
||||
servers and connect to the preferred one:
|
||||
|
||||
Do a lookup for QNAME=_service._protocol.domain, QCLASS=IN,
|
||||
QTYPE=SRV.
|
||||
|
||||
If the reply is NOERROR, ANCOUNT>0 and there is at least one
|
||||
SRV RR which specifies the requested Service and Protocol in
|
||||
the reply:
|
||||
|
||||
If there is precisely one SRV RR, and its Target is "."
|
||||
(the root domain), abort.
|
||||
|
||||
|
||||
|
||||
|
||||
|
||||
Expires May 2001 [Page 6]
|
||||
|
||||
INTERNET-DRAFT DNS SRV RR Novemeber 2000
|
||||
|
||||
|
||||
Else, for all such RR's, build a list of (Priority, Weight,
|
||||
Target) tuples
|
||||
|
||||
Sort the list by priority (lowest number first)
|
||||
|
||||
Create a new empty list
|
||||
|
||||
For each distinct priority level
|
||||
While there are still elements left at this priority
|
||||
level
|
||||
|
||||
Select an element as specified above, in the
|
||||
description of Weight in "The format of the SRV
|
||||
RR" Section, and move it to the tail of the new
|
||||
list
|
||||
|
||||
For each element in the new list
|
||||
|
||||
query the DNS for address records for the Target or
|
||||
use any such records found in the Additional Data
|
||||
section of the earlier SRV response.
|
||||
|
||||
for each address record found, try to connect to the
|
||||
(protocol, address, service).
|
||||
|
||||
else
|
||||
|
||||
Do a lookup for QNAME=domain, QCLASS=IN, QTYPE=A
|
||||
|
||||
for each address record found, try to connect to the
|
||||
(protocol, address, service)
|
||||
|
||||
Notes:
|
||||
|
||||
- Port numbers SHOULD NOT be used in place of the symbolic service
|
||||
or protocol names (for the same reason why variant names cannot
|
||||
be allowed: Applications would have to do two or more lookups).
|
||||
|
||||
- If a truncated response comes back from an SRV query, the rules
|
||||
described in [RFC 2181] shall apply.
|
||||
|
||||
- A client MUST parse all of the RR's in the reply.
|
||||
|
||||
- If the Additional Data section doesn't contain address records
|
||||
for all the SRV RR's and the client may want to connect to the
|
||||
target host(s) involved, the client MUST look up the address
|
||||
record(s). (This happens quite often when the address record
|
||||
has shorter TTL than the SRV or NS RR's.)
|
||||
|
||||
|
||||
|
||||
Expires May 2001 [Page 7]
|
||||
|
||||
INTERNET-DRAFT DNS SRV RR Novemeber 2000
|
||||
|
||||
|
||||
- Future protocols could be designed to use SRV RR lookups as the
|
||||
means by which clients locate their servers.
|
||||
|
||||
Fictional example
|
||||
|
||||
This example uses fictional service "foobar" as an aid in
|
||||
understanding SRV records. If ever service "foobar" is implemented,
|
||||
it is not intended that it will necessarily use SRV records. This is
|
||||
(part of) the zone file for example.com, a still-unused domain:
|
||||
|
||||
$ORIGIN example.com.
|
||||
@ SOA server.example.com. root.example.com. (
|
||||
1995032001 3600 3600 604800 86400 )
|
||||
NS server.example.com.
|
||||
NS ns1.ip-provider.net.
|
||||
NS ns2.ip-provider.net.
|
||||
; foobar - use old-slow-box or new-fast-box if either is
|
||||
; available, make three quarters of the logins go to
|
||||
; new-fast-box.
|
||||
_foobar._tcp SRV 0 1 9 old-slow-box.example.com.
|
||||
SRV 0 3 9 new-fast-box.example.com.
|
||||
; if neither old-slow-box or new-fast-box is up, switch to
|
||||
; using the sysdmin's box and the server
|
||||
SRV 1 0 9 sysadmins-box.example.com.
|
||||
SRV 1 0 9 server.example.com.
|
||||
server A 172.30.79.10
|
||||
old-slow-box A 172.30.79.11
|
||||
sysadmins-box A 172.30.79.12
|
||||
new-fast-box A 172.30.79.13
|
||||
; NO other services are supported
|
||||
*._tcp SRV 0 0 0 .
|
||||
*._udp SRV 0 0 0 .
|
||||
|
||||
|
||||
|
||||
|
||||
|
||||
|
||||
|
||||
|
||||
|
||||
|
||||
|
||||
|
||||
|
||||
|
||||
|
||||
|
||||
|
||||
|
||||
|
||||
Expires May 2001 [Page 8]
|
||||
|
||||
INTERNET-DRAFT DNS SRV RR Novemeber 2000
|
||||
|
||||
|
||||
In this example, a client of the "foobar" service in the
|
||||
"example.com." domain needs an SRV lookup of
|
||||
"_foobar._tcp.example.com." and possibly A lookups of "new-fast-
|
||||
box.example.com." and/or the other hosts named. The size of the SRV
|
||||
reply is approximately 365 bytes:
|
||||
|
||||
30 bytes general overhead
|
||||
20 bytes for the query string, "_foobar._tcp.example.com."
|
||||
130 bytes for 4 SRV RR's, 20 bytes each plus the lengths of "new-
|
||||
fast-box", "old-slow-box", "server" and "sysadmins-box" -
|
||||
"example.com" in the query section is quoted here and doesn't
|
||||
need to be counted again.
|
||||
75 bytes for 3 NS RRs, 15 bytes each plus the lengths of "server",
|
||||
"ns1.ip-provider.net." and "ns2" - again, "ip-provider.net." is
|
||||
quoted and only needs to be counted once.
|
||||
120 bytes for the 6 address records (assuming IPv4 only) mentioned
|
||||
by the SRV and NS RR's.
|
||||
|
||||
IANA Considerations
|
||||
|
||||
The IANA has assigned RR type value 33 to the SRV RR. No other IANA
|
||||
services are required by this document.
|
||||
|
||||
Changes from RFC 2052
|
||||
|
||||
This document obsoletes RFC 2052. The major change from that
|
||||
previous, experimental, version of this specification is that now the
|
||||
protocol and service labels are prepended with an underscore, to
|
||||
lower the probability of an accidental clash with a similar name used
|
||||
for unrelated purposes. Aside from that, changes are only intended
|
||||
to increase the clarity and completeness of the document. This
|
||||
document especially clarifies the use of the Weight field of the SRV
|
||||
records.
|
||||
|
||||
Security Considerations
|
||||
|
||||
The authors believe this RR to not cause any new security problems.
|
||||
Some problems become more visible, though.
|
||||
|
||||
- The ability to specify ports on a fine-grained basis obviously
|
||||
changes how a router can filter packets. It becomes impossible
|
||||
to block internal clients from accessing specific external
|
||||
services, slightly harder to block internal users from running
|
||||
unauthorized services, and more important for the router
|
||||
operations and DNS operations personnel to cooperate.
|
||||
|
||||
- There is no way a site can keep its hosts from being referenced
|
||||
as servers. This could lead to denial of service.
|
||||
|
||||
|
||||
|
||||
Expires May 2001 [Page 9]
|
||||
|
||||
INTERNET-DRAFT DNS SRV RR Novemeber 2000
|
||||
|
||||
|
||||
- With SRV, DNS spoofers can supply false port numbers, as well as
|
||||
host names and addresses. Because this vulnerability exists
|
||||
already, with names and addresses, this is not a new
|
||||
vulnerability, merely a slightly extended one, with little
|
||||
practical effect.
|
||||
|
||||
References
|
||||
|
||||
STD 2: Reynolds, J., and J. Postel, "Assigned Numbers", STD 2, RFC
|
||||
1700, October 1994.
|
||||
|
||||
RFC 1034: Mockapetris, P., "Domain names - concepts and facilities",
|
||||
STD 13, RFC 1034, November 1987.
|
||||
|
||||
RFC 1035: Mockapetris, P., "Domain names - Implementation and
|
||||
Specification", STD 13, RFC 1035, November 1987.
|
||||
|
||||
RFC 974: Partridge, C., "Mail routing and the domain system", STD
|
||||
14, RFC 974, January 1986.
|
||||
|
||||
BCP 14: Bradner, S., "Key words for use in RFCs to Indicate
|
||||
Requirement Levels", BCP 14, RFC 2119, March 1997.
|
||||
|
||||
RFC 2181: Elz, R. and R. Bush, "Clarifications to the DNS
|
||||
Specification", RFC 2181, July 1997.
|
||||
|
||||
RFC 2219: Hamilton, M. and R. Wright, "Use of DNS Aliases for Network
|
||||
Services", BCP 17, RFC 2219, October 1997.
|
||||
|
||||
BCP 14: Bradner, S., "Key words for use in RFCs to Indicate
|
||||
Requirement Levels", BCP 14, RFC 2119, March 1997.
|
||||
|
||||
ARM: Armijo, M., Esibov, L. and P. Leach, "Discovering LDAP
|
||||
Services with DNS", Work in Progress.
|
||||
|
||||
KDC-DNS: Hornstein, K. and J. Altman, "Distributing Kerberos KDC and
|
||||
Realm Information with DNS", Work in Progress.
|
||||
|
||||
|
||||
|
||||
|
||||
|
||||
|
||||
|
||||
|
||||
|
||||
|
||||
|
||||
|
||||
|
||||
|
||||
Expires May 2001 [Page 10]
|
||||
|
||||
INTERNET-DRAFT DNS SRV RR Novemeber 2000
|
||||
|
||||
|
||||
Acknowledgements
|
||||
|
||||
The algorithm used to select from the weighted SRV RRs of equal
|
||||
priority is adapted from one supplied by Dan Bernstein.
|
||||
|
||||
Authors' Addresses
|
||||
|
||||
Arnt Gulbrandsen
|
||||
Trolltech AS
|
||||
Waldemar Thranes gate 98
|
||||
N-0175 Oslo, Norway
|
||||
|
||||
Fax: +47 21604800
|
||||
Phone: +47 21604801
|
||||
EMail: arnt@trolltech.com
|
||||
|
||||
|
||||
Paul Vixie
|
||||
Internet Software Consortium
|
||||
950 Charter Street
|
||||
Redwood City, CA 94063
|
||||
|
||||
Phone: +1 650 779 7001
|
||||
|
||||
|
||||
Levon Esibov
|
||||
Microsoft Corporation
|
||||
One Microsoft Way
|
||||
Redmond, WA 98052
|
||||
|
||||
EMail: levone@microsoft.com
|
||||
|
||||
|
||||
|
||||
|
||||
|
||||
|
||||
|
||||
|
||||
|
||||
|
||||
|
||||
|
||||
|
||||
|
||||
|
||||
|
||||
|
||||
|
||||
|
||||
|
||||
Expires May 2001 [Page 11]
|
||||
|
||||
INTERNET-DRAFT DNS SRV RR Novemeber 2000
|
||||
|
||||
|
||||
Full Copyright Statement
|
||||
|
||||
Copyright (C) The Internet Society (2000). All Rights Reserved.
|
||||
|
||||
This document and translations of it may be copied and furnished to
|
||||
others, and derivative works that comment on or otherwise explain it
|
||||
or assist in its implementation may be prepared, copied, published
|
||||
and distributed, in whole or in part, without restriction of any
|
||||
kind, provided that the above copyright notice and this paragraph are
|
||||
included on all such copies and derivative works. However, this
|
||||
document itself may not be modified in any way, such as by removing
|
||||
the copyright notice or references to the Internet Society or other
|
||||
Internet organizations, except as needed for the purpose of
|
||||
developing Internet standards in which case the procedures for
|
||||
copyrights defined in the Internet Standards process must be
|
||||
followed, or as required to translate it into languages other than
|
||||
English.
|
||||
|
||||
The limited permissions granted above are perpetual and will not be
|
||||
revoked by the Internet Society or its successors or assigns.
|
||||
|
||||
This document and the information contained herein is provided on an
|
||||
"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
|
||||
TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
|
||||
BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
|
||||
HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
|
||||
MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
|
||||
|
||||
Acknowledgement
|
||||
|
||||
Funding for the RFC Editor function is currently provided by the
|
||||
Internet Society.
|
||||
|
||||
|
||||
|
||||
|
||||
|
||||
|
||||
|
||||
|
||||
|
||||
|
||||
|
||||
|
||||
|
||||
|
||||
|
||||
|
||||
|
||||
|
||||
|
||||
Expires May 16, 2001 [Page 12]
|
Loading…
x
Reference in New Issue
Block a user