draft-ietf-dnsop-bad-dns-res-00.txt   draft-ietf-dnsop-bad-dns-res-01.txt 
Internet Engineering Task Force P. Barber DNS Operations M. Larson
Internet-Draft J. Brady Internet-Draft P. Barber
M. Larson Expires: December 22, 2003 VeriSign
VeriSign, Inc. June 23, 2003
November 9, 2001 Expires: May 9, 2002
Observed DNS Resolution Misbehavior Observed DNS Resolution Misbehavior
<draft-ietf-dnsop-bad-dns-res-00.txt> draft-ietf-dnsop-bad-dns-res-01
Status of this memo Status of this Memo
This document is an Internet-Draft and is in full conformance with This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026. all provisions of Section 10 of RFC2026.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that Task Force (IETF), its areas, and its working groups. Note that other
other groups may also distribute working documents as Internet- groups may also distribute working documents as Internet-Drafts.
Drafts.
Internet-Drafts are draft documents valid for a maximum of six Internet-Drafts are draft documents valid for a maximum of six months
months and may be updated, replaced, or obsoleted by other and may be updated, replaced, or obsoleted by other documents at any
documents at any time. It is inappropriate to use Internet-Drafts time. It is inappropriate to use Internet-Drafts as reference
as reference material or to cite them other than as "work in material or to cite them other than as "work in progress."
progress".
The list of current Internet-Drafts can be accessed at The list of current Internet-Drafts can be accessed at http://
http://www.ietf.org/ietf/1id-abstracts.txt 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.
This Internet-Draft will expire on December 22, 2003.
Copyright Notice
Copyright (C) The Internet Society (2003). All Rights Reserved.
Abstract Abstract
This Internet-Draft describes DNS name server and stub resolver This Internet-Draft describes DNS name server and stub resolver
behavior that results in a significant query volume sent to the behavior that results in a significant query volume sent to the root
root and top-level domain (TLD) name servers. In some cases we and top-level domain (TLD) name servers. In some cases we recommend
recommend minor additions to the DNS protocol specification and minor additions to the DNS protocol specification and corresponding
corresponding changes in name server implementations to alleviate changes in name server implementations to alleviate these unnecessary
these unnecessary queries. In one case, we have highlighted queries. In one case, we have highlighted behavior of a popular name
behavior of a popular name server implementation that does not server implementation that does not conform to the DNS specification.
conform to the DNS specification. The recommendations made in this The recommendations made in this document are a direct byproduct of
document are a direct byproduct of observation and analysis of observation and analysis of abnormal query traffic patterns seen at
abnormal query traffic patterns seen at two of the thirteen root two of the thirteen root name servers and all thirteen com/net TLD
name servers and all thirteen com/net/org TLD name servers. name servers.
Conventions used in this document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
this document are to be interpreted as described in [RFC2119]. document are to be interpreted as described in RFC 2119 [1].
Table of contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Observed name server misbehavior . . . . . . . . . . . . . 4 2. Observed name server misbehavior . . . . . . . . . . . . . . 4
2.1 Aggressive requerying for delegation information . . . . 4 2.1 Aggressive requerying for delegation information . . . . . . 4
2.1.1 Recommendation . . . . . . . . . . . . . . . . . . . . 5 2.1.1 Recommendation . . . . . . . . . . . . . . . . . . . . . . . 5
2.2 Repeated queries to lame servers . . . . . . . . . . . . 5 2.2 Repeated queries to lame servers . . . . . . . . . . . . . . 5
2.2.1 Recommendation . . . . . . . . . . . . . . . . . . . . 6 2.2.1 Recommendation . . . . . . . . . . . . . . . . . . . . . . . 6
2.3 Incomplete negative caching implementation . . . . . . . 6 2.3 Incomplete negative caching implementation . . . . . . . . . 6
2.3.1 Recommendation . . . . . . . . . . . . . . . . . . . . 6 2.3.1 Recommendation . . . . . . . . . . . . . . . . . . . . . . . 6
2.4 Inability to follow multiple levels of out-of-zone glue . 6 2.4 Inability to follow multiple levels of out-of-zone glue . . 6
2.4.1 Recommendation . . . . . . . . . . . . . . . . . . . . 7 2.4.1 Recommendation . . . . . . . . . . . . . . . . . . . . . . . 7
3. Observed client misbehavior . . . . . . . . . . . . . . . 8 3. Observed client misbehavior . . . . . . . . . . . . . . . . 8
4. IANA considerations . . . . . . . . . . . . . . . . . . . 9 4. IANA considerations . . . . . . . . . . . . . . . . . . . . 9
5. Security considerations . . . . . . . . . . . . . . . . . 10 5. Security considerations . . . . . . . . . . . . . . . . . . 10
6. Internationalization considerations . . . . . . . . . . . 11 6. Internationalization considerations . . . . . . . . . . . . 11
7. References . . . . . . . . . . . . . . . . . . . . . . . . 12 Normative References . . . . . . . . . . . . . . . . . . . . 12
8. Author's addresses . . . . . . . . . . . . . . . . . . . . 13 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 12
A. Full copyright statement . . . . . . . . . . . . . . . . . 14 Intellectual Property and Copyright Statements . . . . . . . 13
1. Introduction 1. Introduction
Observation of query traffic received by two root name servers and Observation of query traffic received by two root name servers and
the thirteen com/net/org TLD name servers has revealed that a large the thirteen com/net TLD name servers has revealed that a large
proportion of the total traffic often consists of "requeries". A proportion of the total traffic often consists of "requeries". A
requery is the same question (<qname, qtype, qclass>) asked requery is the same question (<qname, qtype, qclass>) asked
repeatedly at an unexpectedly high rate. We have observed repeatedly at an unexpectedly high rate. We have observed requeries
requeries from both a single IP address and multiple IP addresses. from both a single IP address and multiple IP addresses.
By analyzing requery events we have found that the cause of the By analyzing requery events we have found that the cause of the
duplicate traffic is almost always a deficient name server, stub duplicate traffic is almost always a deficient name server, stub
resolver and/or application implementation combined with an resolver and/or application implementation combined with an
operational anomaly. The implementation deficiencies we have operational anomaly. The implementation deficiencies we have
identified to date include well-intentioned recovery attempts gone identified to date include well-intentioned recovery attempts gone
awry, insufficient caching of failures, early abort when multiple awry, insufficient caching of failures, early abort when multiple
levels of glue records must be followed, and aggressive retry by levels of glue records must be followed, and aggressive retry by stub
stub resolvers and/or applications. Anomalies that we have seen resolvers and/or applications. Anomalies that we have seen trigger
trigger requery events include lame delegations, unusual glue requery events include lame delegations, unusual glue records, and
records, and anything that makes all authoritative name servers for anything that makes all authoritative name servers for a zone
a zone unreachable (DoS attacks, crashes, maintenance, routing unreachable (DoS attacks, crashes, maintenance, routing failures,
failures, congestion, etc.). congestion, etc.).
In the following sections, we provide a detailed explanation of the In the following sections, we provide a detailed explanation of the
observed behavior and recommend changes that will reduce the observed behavior and recommend changes that will reduce the requery
requery rate. Some of the changes recommended affect the core DNS rate. Some of the changes recommended affect the core DNS protocol
protocol specification, described principally in [RFC1034], specification, described principally in RFC 1034 [2], RFC 1035 [3]
[RFC1035] and [RFC2181]. and RFC 2181 [4].
2. Observed name server misbehavior 2. Observed name server misbehavior
2.1 Aggressive requerying for delegation information 2.1 Aggressive requerying for delegation information
There can be times when every name server in a zone's NS RRset is There can be times when every name server in a zone's NS RRset is
unreachable (e.g., during a network outage), unavailable (e.g., the unreachable (e.g., during a network outage), unavailable (e.g., the
name server process is not running on the server host) or name server process is not running on the server host) or
misconfigured (e.g., the name server is not authoritative for the misconfigured (e.g., the name server is not authoritative for the
given zone, also known as "lame"). Consider a name server that given zone, also known as "lame"). Consider a name server that
attempts to resolve a recursive query for a domain name in such a attempts to resolve a recursive query for a domain name in such a
zone and discovers that none of the zone's name servers can provide zone and discovers that none of the zone's name servers can provide
an answer. We have observed a recursive name server implementation an answer. We have observed a recursive name server implementation
that then verifies the zone's NS RRset in its cache by querying for that then verifies the zone's NS RRset in its cache by querying for
the zone's delegation information: it sends a query for the zone's the zone's delegation information: it sends a query for the zone's NS
NS RRset to one of the parent zone's name servers. RRset to one of the parent zone's name servers.
For example, suppose that example.com has the following NS RRset: For example, suppose that example.com has the following NS RRset:
example.com. IN NS ns1.example.com. example.com. IN NS ns1.example.com.
example.com. IN NS ns2.example.com. example.com. IN NS ns2.example.com.
Upon receipt of a query for www.example.com and assuming that Upon receipt of a query for www.example.com and assuming that neither
neither ns1.example.com nor ns2.example.com can provide an answer, ns1.example.com nor ns2.example.com can provide an answer, this
this recursing name server implementation immediately queries a com recursive name server implementation immediately queries a com zone
zone name server for the example.com NS RRset to verify it has the name server for the example.com NS RRset to verify it has the proper
proper delegation information. This name server implementation delegation information. This name server implementation performs
performs this query to a zone's parent zone for each recursive this query to a zone's parent zone for each recursive query it
query it receives that fails because of a completely unresponsive receives that fails because of a completely unresponsive set of name
set of name servers for the target zone. Consider the effect when servers for the target zone. Consider the effect when a popular zone
a popular zone experiences a catastrophic failure of all its name experiences a catastrophic failure of all its name servers: now every
servers: now every recursive query for domain names in that zone recursive query for domain names in that zone sent to this name
sent to this name server implementation results in a query to the server implementation results in a query to the failed zone's parent
failed zone's parent name servers. On one occasion when several name servers. On one occasion when several dozen popular zones
dozen popular zones became unreachable, the query load to the became unreachable, the query load to the com/net name servers
com/net/org name servers increased by 50%. increased by 50%.
We believe this verification query is not reasonable. Consider the We believe this verification query is not reasonable. Consider the
circumstances: When a recursing name server is resolving a query circumstances: When a recursing name server is resolving a query for
for a domain name in a zone it has not previously searched, it uses a domain name in a zone it has not previously searched, it uses the
the list of name servers in the referral from the target zone's list of name servers in the referral from the target zone's parent.
parent. If on its first attempt to search the target zone, none of If on its first attempt to search the target zone, none of the name
the name servers in the referral are reachable, a verification servers in the referral are reachable, a verification query to the
query to the parent is pointless: this query to the parent would parent is pointless: this query to the parent would come so quickly
come so quickly on the heels of the referral that it would be on the heels of the referral that it would be almost certain to
almost certain to contain the same list of name servers. The contain the same list of name servers. The chance of discovering any
chance of discovering any new information is slim. new information is slim.
The other possibility is that the recursing name server The other possibility is that the recursing name server successfully
successfully contacts one of the target zone's name servers and contacts one of the target zone's name servers and then caches the NS
then caches the NS RRset from the authority section of a response, RRset from the authority section of a response, the proper behavior
the proper behavior according to section 5.4.1 of [RFC2181], according to section 5.4.1 of RFC 2181 [4], because the NS RRset from
because the NS RRset from the target zone is more trustworthy than the target zone is more trustworthy than delegation information from
delegation information from the parent zone. If, while processing the parent zone. If, while processing a subsequent recursive query,
a subsequent recursive query, the recursing name server discovers the recursing name server discovers that none of the name servers
that none of the name servers specified in the cached NS RRset is specified in the cached NS RRset is available or authoritative,
available or authoritative, querying the parent would be wrong. An querying the parent would be wrong. An NS RRset from the parent zone
NS RRset from the parent zone would now be less trustworthy than would now be less trustworthy than data already in the cache.
data already in the cache.
For this query of the parent zone to be useful, the target zone's For this query of the parent zone to be useful, the target zone's
entire set of name servers would have to change AND the former set entire set of name servers would have to change AND the former set of
of name servers would have to be deconfigured and/or decomissioned name servers would have to be deconfigured and/or decomissioned AND
AND the delegation information in the parent zone would have to be the delegation information in the parent zone would have to be
updated with the new set of name servers, all within the TTL of the updated with the new set of name servers, all within the TTL of the
target zone's NS RRset. We believe this scenario is uncommon: target zone's NS RRset. We believe this scenario is uncommon:
administrative best practices dictate that changes to a zone's set administrative best practices dictate that changes to a zone's set of
of name servers happen gradually, with servers that are removed name servers happen gradually, with servers that are removed from the
from the NS RRset left authoritative for the zone as long as NS RRset left authoritative for the zone as long as possible. The
possible. The scenarios that we can envision that would benefit scenarios that we can envision that would benefit from the parent
from the parent requery behavior do not outweigh its damaging requery behavior do not outweigh its damaging effects.
effects.
2.1.1 Recommendation 2.1.1 Recommendation
Name servers offering recursion MUST NOT send a query for the NS Name servers offering recursion MUST NOT send a query for the NS
RRset of a non-responsive zone to any of the name servers for that RRset of a non-responsive zone to any of the name servers for that
zone's parent zone. For the purposes of this injunction, a non- zone's parent zone. For the purposes of this injunction, a
responsive zone is defined as a zone for which every name server non-responsive zone is defined as a zone for which every name server
listed in the zone's NS RRset: listed in the zone's NS RRset:
(1) is not authoritative for the zone (i.e., lame), or, 1. is not authoritative for the zone (i.e., lame), or,
(2) returns a server failure response (SERVFAIL), or,
(3) is dead or unreachable according to section 7.2 of [RFC2308]. 2. returns a server failure response (RCODE=2), or,
3. is dead or unreachable according to section 7.2 of RFC 2308 [5].
2.2 Repeated queries to lame servers 2.2 Repeated queries to lame servers
Section 2.1 describes a catastrophic failure: when every name Section 2.1 describes a catastrophic failure: when every name server
server for a zone is unable to provide an answer for one reason or for a zone is unable to provide an answer for one reason or another.
another. A more common occurrence is a subset of a zone's name A more common occurrence is a subset of a zone's name servers being
servers being unavailable or misconfigured. Different failure unavailable or misconfigured. Different failure modes have different
modes have different expected durations. Some symptoms indicate expected durations. Some symptoms indicate problems that are
problems that are potentially transient: various types of ICMP potentially transient: various types of ICMP unreachable messages
unreachable messages because a name server process is not running because a name server process is not running or a host or network is
or a host or network is unreachable, or a complete lack of a unreachable, or a complete lack of a response to a query. Such
response to a query. Such responses could be the result of a host responses could be the result of a host rebooting or temporary
rebooting or temporary outages; these events don't necessarily outages; these events don't necessarily require any human
require any human intervention and can be reasonably expected to be intervention and can be reasonably expected to be temporary.
temporary.
Other symptoms clearly indicate a condition requiring human Other symptoms clearly indicate a condition requiring human
intervention, such as lame server: if a name server is intervention, such as lame server: if a name server is misconfigured
misconfigured and not authoritative for a zone delegated to it, it and not authoritative for a zone delegated to it, it is reasonable to
is reasonable to assume that this condition has potential to last assume that this condition has potential to last longer than
longer than unreachability or unresponsiveness. Consequently, unreachability or unresponsiveness. Consequently, repeated queries
repeated queries to known lame servers are not useful. In this to known lame servers are not useful. In this case of a condition
case of a condition with potential to persist for a long time, a with potential to persist for a long time, a better practice would be
better practice would be to maintain a list of known lame servers to maintain a list of known lame servers and avoid querying them
and avoid querying them repeatedly in a short interval. repeatedly in a short interval.
2.2.1 Recommendation 2.2.1 Recommendation
Name servers offering recursion SHOULD cache name servers that they Name servers offering recursion SHOULD cache name servers that they
discover are not authoritative for zones delegated to them (i.e. discover are not authoritative for zones delegated to them (i.e. lame
lame servers). Lame servers MUST be cached against the specific servers). Lame servers MUST be cached against the specific query
query tuple <zone name, class, server IP address>. Zone name can tuple <zone name, class, server IP address>. Zone name can be
be derived from the owner name of the NS record that was referenced derived from the owner name of the NS record that was referenced to
to query the name server that was discovered to be lame. query the name server that was discovered to be lame.
Implementations that perform lame server caching MUST refrain from Implementations that perform lame server caching MUST refrain from
sending queries to known lame servers based on a time interval from sending queries to known lame servers based on a time interval from
when the server is discovered to be lame. A minimum interval of when the server is discovered to be lame. A minimum interval of
thirty minutes is RECOMMENDED. thirty minutes is RECOMMENDED.
2.3 Incomplete negative caching implementation 2.3 Incomplete negative caching implementation
A widely distributed name server implementation does not properly A widely distributed name server implementation does not properly
implement negative caching as described in [RFC2308]. In implement negative caching as described in RFC 2308 [5]. In
particular, this implementation does not cache NODATA responses. particular, this implementation does not cache NODATA responses.
Such a response indicates that the queried domain name exists but Such a response indicates that the queried domain name exists but has
has no records of the desired type. See section 2.2 of [RFC2308] no records of the desired type. See Section 2.2 of RFC 2308 [5] for
for information on how NODATA responses are indicated. information on how NODATA responses are indicated.
2.3.1 Recommendation 2.3.1 Recommendation
Vendors of any name server implementations that do not comply with Vendors of any name server implementations that do not comply with
[RFC2308] are encouraged to bring their software into conformance. RFC 2308 [5] are encouraged to bring their software into conformance.
2.4 Inability to follow multiple levels of out-of-zone glue 2.4 Inability to follow multiple levels of out-of-zone glue
Some name server implementations are unable to follow more than one Some name server implementations are unable to follow more than one
level of out-of-zone glue. For example, consider the following level of out-of-zone glue. For example, consider the following
delegations: delegations:
foo.example. IN NS ns1.example.com. foo.example. IN NS ns1.example.com.
foo.example. IN NS ns2.example.com. foo.example. IN NS ns2.example.com.
example.com. IN NS ns1.test.example.net. example.com. IN NS ns1.test.example.net.
example.com. IN NS ns2.test.example.net. example.com. IN NS ns2.test.example.net.
test.example.net. IN NS ns1.test.example.net. test.example.net. IN NS ns1.test.example.net.
test.example.net. IN NS ns2.test.example.net. test.example.net. IN NS ns2.test.example.net.
A name server processing a recursive query for www.foo.example must A name server processing a recursive query for www.foo.example must
follow two levels of indirection, first obtaining address records follow two levels of indirection, first obtaining address records for
for ns1.test.example.net and/or ns2.test.example.net in order to ns1.test.example.net and/or ns2.test.example.net in order to obtain
obtain address records for ns1.example.com and/or ns2.example.com address records for ns1.example.com and/or ns2.example.com in order
in order to query those name servers for the address records of to query those name servers for the address records of
www.foo.example. While this situation may appear contrived, we www.foo.example. While this situation may appear contrived, we have
have seen multiple similar occurrences and expect more as the new seen multiple similar occurrences and expect more as the new generic
generic top-level domains (gTLDs) become active. We anticipate top-level domains (gTLDs) become active. We anticipate many zones in
many zones in the new gTLDs will use name servers in other gTLDs, the new gTLDs will use name servers in other gTLDs, increasing the
increasing the amount of inter-zone glue. amount of inter-zone glue.
2.4.1 Recommendation 2.4.1 Recommendation
Certainly constructing a delegation that relies on multiple levels Certainly constructing a delegation that relies on multiple levels of
of out-of-zone glue is not a good administrative practice. This out-of-zone glue is not a good administrative practice. This issue
issue could be mitigated with an operational injunction in an RFC could be mitigated with an operational injunction in an RFC to
to refrain from construction of such delegations. In our opinion refrain from construction of such delegations. In our opinion the
the practice is widespread enough to merit clarifications to the practice is widespread enough to merit clarifications to the DNS
DNS protocol specification to permit it on a limited basis. protocol specification to permit it on a limited basis.
Name servers offering recursion SHOULD be able to handle at least Name servers offering recursion SHOULD be able to handle at least
three levels of indirection resulting from out-of-zone glue. three levels of indirection resulting from out-of-zone glue.
3. Observed client misbehavior 3. Observed client misbehavior
We have observed situations where a zone's name servers are We have observed situations where a zone's name servers are
misconfigured or unavailable, resulting in a SERVFAIL response from misconfigured or unavailable, resulting in a SERVFAIL response from a
a recursive name server in response to queries for domain names in recursive name server in response to queries for domain names in that
that zone. In some instances, we then observe many repeated zone. In some instances, we then observe many repeated queries (on
queries (on the order of hundreds per second) to the com/net/org the order of hundreds per second) to the com/net name servers for
name servers for domain names in the affected zones. Sometimes the domain names in the affected zones. Sometimes the queries originate
queries originate from multiple source IP addresses, while at other from multiple source IP addresses, while at other times a single
times a single source address sends many repeated queries. This source address sends many repeated queries. This behavior appears to
behavior appears to be triggered by a SERVFAIL response (i.e., upon be triggered by a SERVFAIL response (i.e., upon investigation, the
investigation, the <qname, qtype, qclass> of a repeated query at <qname, qtype, qclass> of a repeated query at the com/net name
the com/net/org name servers produces a SERVFAIL response when sent servers produces a SERVFAIL response when sent to a local recursive
to a local recursive name server.) name server.)
We suspect that some DNS clients (i.e., stub resolvers) and/or We suspect that some DNS clients (i.e., stub resolvers) and/or
application programs have overzealous retransmission algorithms application programs have overzealous retransmission algorithms that
that are trigged by a SERVFAIL response. Unfortunately, we have are trigged by a SERVFAIL response. Unfortunately, we have not been
not been able to isolate particular implementations. The authors able to isolate particular implementations. The authors encourage
encourage and welcome reports of DNS clients and applications with and welcome reports of DNS clients and applications with overzealous
overzealous retransmission algorithms. retransmission algorithms.
4. IANA considerations 4. IANA considerations
There are no new IANA considerations introduced by this Internet- There are no new IANA considerations introduced by this
Draft. Internet-Draft.
5. Security considerations 5. Security considerations
Nameserver, stub resolver and application misbehaviors identical or Nameserver, stub resolver and application misbehaviors identical or
similar to those observed and discussed in this document expose similar to those observed and discussed in this document expose root
root and TLD name server constellations to increased risk of both and TLD name server constellations to increased risk of both
intentional and unintentional denial of service. intentional and unintentional denial of service.
We believe that implementation of the recommendations offered in We believe that implementation of the recommendations offered in this
this document will reduce the requery traffic seen at root and TLD document will reduce the requery traffic seen at root and TLD name
name servers, thus reducing the opportunity for an attacker to use servers, thus reducing the opportunity for an attacker to use such
such requerying to his or her advantage. requerying to his or her advantage.
6. Internationalization considerations 6. Internationalization considerations
We do not believe this document introduces any new We do not believe this document introduces any new
internationalization considerations to the DNS protocol internationalization considerations to the DNS protocol
specification. specification.
7. References Normative References
[RFC1034] - Domain Names - Concepts and Facilities, P. Mockapetris, [1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
November 1987. Levels", BCP 14, RFC 2119, March 1997.
[RFC1035] - Domain Names - Implementation and Specifications, P. [2] Mockapetris, P., "Domain names - concepts and facilities", STD
Mockapetris, November 1987. 13, RFC 1034, November 1987.
[RFC2119] - Key Words for Use in RFCs to Indicate Requirement [3] Mockapetris, P., "Domain names - implementation and
Levels, S. Bradner, March 1997. specification", STD 13, RFC 1035, November 1987.
[RFC2181] - Clarifications to the DNS Specification, R. Elz, R. [4] Elz, R. and R. Bush, "Clarifications to the DNS Specification",
Bush, July 1997. RFC 2181, July 1997.
[RFC2308] - Negative Caching of DNS Queries (DNS NCACHE), M. [5] Andrews, M., "Negative Caching of DNS Queries (DNS NCACHE)", RFC
Andrews, March 1998. 2308, March 1998.
8. Authors' addresses Authors' Addresses
Piet Barber Matt Larson
VeriSign Global Registry Services VeriSign, Inc.
21345 Ridgetop Circle 21345 Ridgetop Circle
Dulles, VA 20166-6503 Dulles, VA 20166-6503
USA USA
pbarber@verisign.com
John Brady EMail: mlarson@verisign.com
VeriSign Global Registry Services
21345 Ridgetop Circle
Dulles, VA 20166-6503
USA
jbrady@verisign.com
Matt Larson Piet Barber
VeriSign Global Registry Services VeriSign, Inc.
21345 Ridgetop Circle 21345 Ridgetop Circle
Dulles, VA 20166-6503 Dulles, VA 20166-6503
USA USA
mlarson@verisign.com
A. Full copyright statement EMail: pbarber@verisign.com
Copyright (C) The Internet Society 2001. All Rights Reserved. Intellectual Property Statement
The IETF takes no position regarding the validity or scope of any
intellectual property or other rights that might be claimed to
pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights
might or might not be available; neither does it represent that it
has made any effort to identify any such rights. Information on the
IETF's procedures with respect to rights in standards-track and
standards-related documentation can be found in BCP-11. Copies of
claims of rights made available for publication and any assurances of
licenses to be made available, or the result of an attempt made to
obtain a general license or permission for the use of such
proprietary rights by implementors or users of this specification can
be obtained from the IETF Secretariat.
The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights which may cover technology that may be required to practice
this standard. Please address the information to the IETF Executive
Director.
Full Copyright Statement
Copyright (C) The Internet Society (2003). 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 others, and derivative works that comment on or otherwise explain it
it or assist in its implementation may be prepared, copied, or assist in its implementation may be prepared, copied, published
published and distributed, in whole or in part, without restriction and distributed, in whole or in part, without restriction of any
of any kind, provided that the above copyright notice and this kind, provided that the above copyright notice and this paragraph are
paragraph are included on all such copies and derivative works. included on all such copies and derivative works. However, this
However, this document itself may not be modified in any way, such document itself may not be modified in any way, such as by removing
as by removing the copyright notice or references to the Internet the copyright notice or references to the Internet Society or other
Society or other Internet organizations, except as needed for the Internet organizations, except as needed for the purpose of
purpose of developing Internet standards in which case the developing Internet standards in which case the procedures for
procedures for copyrights defined in the Internet Standards process copyrights defined in the Internet Standards process must be
must be followed, or as required to translate it into languages followed, or as required to translate it into languages other than
other than English. English.
The limited permissions granted above are perpetual and will not be The limited permissions granted above are perpetual and will not be
revoked by the Internet Society or its successors or assigns. revoked by the Internet Society or its successors or assignees.
This document and the information contained herein is provided on This document and the information contained herein is provided on an
an "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
ENGINEERING TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Acknowledgement Acknowledgement
Funding for the RFC Editor function is currently provided by the Funding for the RFC Editor function is currently provided by the
Internet Society. Internet Society.
 End of changes. 

This html diff was produced by rfcdiff 1.23, available from http://www.levkowetz.com/ietf/tools/rfcdiff/