< draft-eastlake-dnsext-cookies-01.txt   draft-eastlake-dnsext-cookies-02.txt >
INTERNET-DRAFT Donald E. Eastlake 3rd INTERNET-DRAFT Donald E. Eastlake 3rd
Motorola Laboratories Intended Status: Proposed Standard Motorola Laboratories
Expires: April 2007 October 2006 Expires: February 2008 August 2007
Domain Name System (DNS) Cookies Domain Name System (DNS) Cookies
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<draft-eastlake-dnsext-cookies-01.txt> <draft-eastlake-dnsext-cookies-02.txt>
Status of This Document Status of This Document
By submitting this Internet-Draft, each author represents that any By submitting this Internet-Draft, each author represents that any
applicable patent or other IPR claims of which he or she is aware applicable patent or other IPR claims of which he or she is aware
have been or will be disclosed, and any of which he or she becomes have been or will be disclosed, and any of which he or she becomes
aware will be disclosed, in accordance with Section 6 of BCP 79. aware will be disclosed, in accordance with Section 6 of BCP 79.
This draft is intended to be become a Proposed Standard RFC. This draft is intended to be become a Proposed Standard RFC.
Distribution of this document is unlimited. Comments should be sent Distribution of this document is unlimited. Comments should be sent
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The list of current Internet-Drafts can be accessed at The list of current Internet-Drafts can be accessed at
http://www.ietf.org/1id-abstracts.html http://www.ietf.org/1id-abstracts.html
The list of Internet-Draft Shadow Directories can be accessed at The list of Internet-Draft Shadow Directories can be accessed at
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Abstract Abstract
DNS cookies are a light-weight DNS transaction security mechanism. DNS cookies are a light-weight DNS transaction security mechanism.
They provides limited protection to DNS servers and resolvers against They provides limited protection to DNS servers and resolvers against
a variety of increasingly common denial-of-service and cache a variety of increasingly common denial-of-service and cache
poisoning attacks by off-path attackers. poisoning or forgery attacks by off-path attackers.
Copyright Notice
Copyright (C) The Internet Society (2006).
INTERNET-DRAFT DNS Cookies INTERNET-DRAFT DNS Cookies
Table of Contents Table of Contents
Status of This Document....................................1 Status of This Document....................................1
Abstract...................................................1 Abstract...................................................1
Copyright Notice...........................................1
Table of Contents..........................................2 Table of Contents..........................................2
1. Introduction............................................3 1. Introduction............................................3
1.1 Contents of This Document..............................3 1.1 Contents of This Document..............................3
1.2 Definitions............................................3 1.2 Definitions............................................3
2. Threats Considered......................................4
2.1 Denial-of-Service Attacks..............................4 2. Threats Considered......................................5
2.1.1 DNS Server Denial-of-Service.........................4 2.1 Denial-of-Service Attacks..............................5
2.1.1 DNS Server Denial-of-Service.........................5
2.1.2 Selected Host Denial-of-Service......................5 2.1.2 Selected Host Denial-of-Service......................5
2.2 Cache Poisoning Attacks................................5 2.2 Cache Poisoning and Answer Forgery Attacks.............6
3. Comments on Existing DNS Security.......................5 3. Comments on Existing DNS Security.......................6
4. The COOKIE OPT option...................................6 3.1 Existing DNS Data Security.............................6
4.1 Resolver Cookies.......................................7 3.2 DNS Message or Transaction Security....................7
4.2 Server Cookies.........................................8 3.3 Conclusions on Existing DNS Security...................7
5. General Policies and Implementation.....................8
5.1 Resolver Policies and Implementation...................9
5.2 Server Policies and Implementation.....................9
5.3 Implementation Requirements...........................10
6. NAT and AnyCast Considerations.........................10
7. IANA Considerations....................................12
8. Security Considerations................................12
9. Copyright and Disclaimer...............................13
10. Normative References..................................13
11. Informative References................................14
Author's Address..........................................15 4. The COOKIE OPT option...................................8
Additional IPR Provisions.................................15 4.1 Resolver Cookies.......................................8
Expiration and File Name..................................15 4.2 Server Cookies.........................................9
5. DNS Cookie Policies and Implementation Requirements.....9
5.1 Resolver Policies and Implementation..................10
5.2 Server Policies and Implementation....................10
5.3 Implementation Requirements...........................11
6. NAT and AnyCast Considerations.........................11
7. IANA Considerations....................................14
8. Security Considerations................................14
9. Normative References...................................15
10. Informative References................................15
Author's Address..........................................17
Copyright and Disclaimer..................................17
Additional IPR Provisions.................................17
Expiration and File Name..................................18
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1. Introduction 1. Introduction
The Domain Name System (DNS) provides a replicated distributed The Domain Name System (DNS) provides a replicated distributed
database which stores "resource records" (RRs) under hierarchical database which stores "resource records" (RRs) under hierarchical
domain names. DNS data is structured into CLASSes and zones which domain names. DNS data is structured into CLASSes and zones which
can be independently maintained. See [STD13], [RFC2181] familiarity can be independently maintained. See [STD13] and [RFC2181]
with which is assumed. familiarity with which is assumed.
As with many core Internet protocols, DNS was designed at a time when As with many core Internet protocols, DNS was designed at a time when
the Internet had only a small pool of trusted users. As the Internet the Internet had only a small pool of trusted users. As the Internet
has exploded to a global information utility the DNS has increasingly has exploded to a global information utility the DNS has increasingly
been subject to abuse and been used as a vector for abuse. been subject to abuse and been used as a vector for abuse.
This document describes DNS cookies, a light-weight DNS transaction This document describes DNS cookies, a light-weight DNS transaction
security mechanism specified as an OPT [RFC2671] option. They security mechanism specified as an OPT [RFC2671] option. They
provides limited protection to DNS servers and resolvers against a provides limited protection to DNS servers and resolvers against a
variety of increasingly common denial-of-service and cache poisoning variety of increasingly common denial-of-service and cache poisoning
attacks by off-path attackers. forgery attacks by off-path attackers.
1.1 Contents of This Document 1.1 Contents of This Document
In Section 2, we discuss the threats against which DNS cookies In Section 2, we discuss the threats against which DNS cookies
provides some protection. provides some protection.
Section 3 describes existing DNS security mechanisms and why they are Section 3 describes existing DNS security mechanisms and why they are
not adequate substitutes for DNS cookies. not adequate substitutes for DNS cookies.
Section 4 describes the COOKIE OPT option including recommendations Section 4 describes the COOKIE OPT option including recommendations
for calculating Resolver and Server Cookies. for calculating Resolver and Server Cookies.
Section 5 describes the processing of COOKIE OPT optionby resolvers Section 5 describes the processing of COOKIE OPT options by resolvers
and server and policies for such processing. and server and policies for such processing.
Section 6 discusses some NAT and anycast related DNS Cookies design Section 6 discusses some NAT and anycast related DNS Cookies design
considerations. considerations.
Sections 7 and 8 describe IANA and Security Considerations. Sections 7 and 8 describe IANA and Security Considerations.
1.2 Definitions 1.2 Definitions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
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document are to be interpreted as described in [RFC2119]. document are to be interpreted as described in [RFC2119].
An "off-path attacker", for a particular DNS resolver and server, is An "off-path attacker", for a particular DNS resolver and server, is
defined as an attacker which cannot observe the legitimate plain text defined as an attacker which cannot observe the legitimate plain text
INTERNET-DRAFT DNS Cookies INTERNET-DRAFT DNS Cookies
DNS requests and responses between that resolver and server. DNS requests and responses between that resolver and server.
"Soft state" indicates information learned or derived by a host which "Soft state" indicates information learned or derived by a host which
may be discarded when indicated by the policies of that host. For may be discarded when indicated by the policies of that host but can
example, it could be discarded after a period of time or when storage be later re-instantiated if needed. For example, it could be
for caching such data becomes full. If operations requiring that soft discarded after a period of time or when storage for caching such
state continue after it has been discarded, it will be automatically data becomes full. If operations requiring that soft state continue
re-generated, albeit at some cost. after it has been discarded, it will be automatically re-generated,
albeit at some cost.
"Silently discarded" indicates that there are no DNS protocol message "Silently discarded" indicates that there are no DNS protocol message
consequences; however, it is RECOMMENDED that appropriate debugging consequences; however, it is RECOMMENDED that appropriate debugging
network management facilities be included in implementations, such as network management facilities be included in implementations, such as
a counter of the occurrences of each type of such events. a counter of the occurrences of each type of such events.
The term "IP address" is used herein in a length independent manner The term "IP address" is used herein in a length independent manner
and refers interchangeably to IPv4 and IPv6 addresses. and refers to address formats including IPv4 and IPv6.
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2. Threats Considered 2. Threats Considered
DNS cookies are intended to provide significant but limited DNS cookies are intended to provide significant but limited
protection against certain denial-of-service and cache poisoning protection against certain denial-of-service and cache poisoning or
attacks by off-path attackers described below. answer forgery attacks by off-path attackers described below.
2.1 Denial-of-Service Attacks 2.1 Denial-of-Service Attacks
The normal form of the denial-of-service attacks considered herein is The canonical form of the denial-of-service attacks considered herein
to send DNS requests with forged source IP addresses to a server. The is to send DNS requests with forged source IP addresses to a server.
intent can be to attack that server or a selected host as described The intent can be to attack that server or a selected host as
below. described below.
2.1.1 DNS Server Denial-of-Service 2.1.1 DNS Server Denial-of-Service
DNS requests that are accepted cause work on the part of DNS servers. DNS requests that are accepted cause work on the part of DNS servers.
This is particularly true for recursive servers which may issue one This is particularly true for recursive servers which may issue one
or more requests and process the responses thereto in order to or more requests and process the responses thereto in order to
determine their response to the initial query. And the situation is determine their response to the initial query. And the situation is
even worse for recursive servers implementing DNSSEC [RFC4033], even worse for recursive servers implementing DNSSEC [RFC4033],
[RFC4034], [RFC4035] because they may be induced to perform [RFC4034], [RFC4035] because they may be induced to perform
burdensome public key cryptographic computations in attempts to burdensome public key cryptographic computations in attempts to
verify the authenticity of data they retrieve in trying to answer the verify the authenticity of data they retrieve while trying to answer
request. the request.
While the burden cause by such requests is not dependent on a forged
IP source address, the use of such addresses makes
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+ the source of the requests causing the denial-of-service requests The computational or communications burden cause by such requests is
to be harder to find and not dependent on a forged IP source address, but the use of such
addresses makes
+ the source of the requests causing the denial-of-service attack to
be harder to find and
+ administrative restriction of the IP addresses from which such + administrative restriction of the IP addresses from which such
requests should be honored harder to enforce. requests should be honored harder to accurately specify.
Use of DNS cookies almost always enables a server to reject forged
queries from an off path attacker with relative ease, certainly
before any recursive queries or public key cryptographic operations
are performed.
2.1.2 Selected Host Denial-of-Service 2.1.2 Selected Host Denial-of-Service
Request with a forged IP address causes a response to be sent to that A request with a forged IP address generally causes a response to be
forged IP address. Thus the forging of many such requests can, sent to that forged IP address. Thus the forging of many such
indirectly, result in enough traffic being sent to the forged IP requests with a particular source IP address can result in enough
address to interfere with service to the host at the IP address. traffic being sent to the forged IP address to interfere with service
Furthermore, it is generally easy in the DNS to create short requests
that produce much longer responses. Thus a DNS server can be used as INTERNET-DRAFT DNS Cookies
not only a way to obscure the true source of an attack but as a
traffic amplifier to make the attack more effective. to the host at the IP address. Furthermore, it is generally easy in
the DNS to create short requests that produce much longer responses.
Thus a DNS server can be used as not only a way to obscure the true
source of an attack but as a traffic amplifier to make the attack
more effective.
Use of DNS cookies severely limits the traffic amplification that can Use of DNS cookies severely limits the traffic amplification that can
be obtained by attackers off path for the server and the attacked be obtained by attackers off path for the server and the attacked
host. Enforced DNS cookies would make it hard for an off path host. Enforced DNS cookies would make it hard for an off path
attacker to cause any more than a brief error response to be send to attacker to cause any more than a brief error response to be send to
a forged IP address. Furthermore, DNS cookies make it more effective a forged IP address. Furthermore, DNS cookies make it more effective
to implement a rate limiting scheme for bad DNS cookie error response to implement a rate limiting scheme for bad DNS cookie error
from the server. Such a scheme would further restrict selected host responses from the server. Such a scheme would further restrict
denial-of-service traffic from that server. selected host denial-of-service traffic from that server.
2.2 Cache Poisoning Attacks 2.2 Cache Poisoning and Answer Forgery Attacks
The form of the cache poisoning attacks considered is to send forged The form of the cache poisoning attacks considered is to send forged
replies to a resolver. Modern network speeds for well connected hosts replies to a resolver. Modern network speeds for well connected hosts
are such that, by forging replies from the IP addresses of heavily are such that, by forging replies from the IP addresses of heavily
used DNS servers and for popular names to a heavily used resolver, used DNS servers and for popular names to a heavily used resolver,
there can be an unacceptably high probability of randomly coming up there can be an unacceptably high probability of randomly coming up
with a reply that will be accepted and cause false DNS information to with a reply that will be accepted and cause false DNS information to
be cached by that resolver. This can be used to facilitate phishing be cached by that resolver. This can be used to facilitate phishing
attacks and other diversion of legitimate traffic to a compromised or attacks and other diversion of legitimate traffic to a compromised or
malicious host such as a web server. malicious host such as a web server.
In a similar manner it is possible, under some circumstances to send
forged answers that will be accepted by resolvers with an
unacceptably high probability.
3. Comments on Existing DNS Security 3. Comments on Existing DNS Security
Two forms of security have been added to DNS: Two forms of security have been added to DNS, data security and
message or transaction security.
The first, called DNSSEC and described in [RFC4033], [RFC4034], and 3.1 Existing DNS Data Security
[RFC4035], provides data origin authentication and authenticated
denial of existence. It is being deployed very slowly and, in any DNS data security is one part of DNSSEC and is described in
[RFC4033], [RFC4034], and [RFC4035]. It provides data origin
authentication and authenticated denial of existence. It is being
deployed slowly and, in any case, can make some denial-of-service
attacks worse because of the high cryptographic computational load it
can require and the increased size in DNS packets that it tends to
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case, can make some denial-of-service attacks worse because of the produce.
high cryptographic computational load it can require and the
increased size in DNS packets that it can produces. 3.2 DNS Message or Transaction Security
The second form of security which has been added to DNS provides The second form of security which has been added to DNS provides
"transaction" security through TSIG [RFC2845] or SIG(0) [RFC2931]. "transaction" security through TSIG [RFC2845] or SIG(0) [RFC2931].
TSIG could provide near perfect protection against the attacks for TSIG could provide near perfect protection against the attacks for
which DNS cookies provide weak and incomplete protection; however, which DNS cookies provide weak and incomplete protection; however,
TSIG is hard to deploy in the general Internet because of the burden TSIG is hard to deploy in the general Internet because of the burden
it imposes of pre-agreement and key distribution between pairs of it imposes of pre-agreement and key distribution between pairs of
resolvers and servers and because it requires time synchronization resolvers and servers and because it requires time synchronization
between resolver and server. between resolver and server.
TKEY [RFC2930] can solve the problem of key distribution for TSIG but TKEY [RFC2930] can solve the problem of key distribution for TSIG but
some modes of TKEY impose substantial cryptographic computations some modes of TKEY impose substantial cryptographic computations
loads and can be dependent on the deployment of DNSSEC. loads and can be dependent on the deployment of DNSSEC.
SIG(0) provides less protection than TSIG or, in one way, even DNS SIG(0) provides less denial of service protection than TSIG or, in
cookies, because it does not authentication requests, only complete one way, even DNS cookies, because it does not authenticate requests,
transactions. In any case, it also depends on the deployment of only complete transactions. In any case, it also depends on the
DNSSEC and requires computationally burdensome public key deployment of DNSSEC and requires computationally burdensome public
cryptographic operations. key cryptographic operations.
3.3 Conclusions on Existing DNS Security
Thus, none of the previous forms of DNS security are a suitable Thus, none of the previous forms of DNS security are a suitable
substitute for DNS cookies, which provide light weight transaction substitute for DNS cookies, which provide light weight message
authentication of DNS requests and responses with no requirement for authentication of DNS requests and responses with no requirement for
pre-configuration. pre-configuration.
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4. The COOKIE OPT option 4. The COOKIE OPT option
COOKIE is an OPT RR [RFC2671] option that can be included once in the COOKIE is an OPT RR [RFC2671] option that can be included once in the
RDATA portion of an OPT RR in DNS requests and responses. RDATA portion of an OPT RR in DNS requests and responses.
The option is encoded into 22 bytes as shown below. The option is encoded into 22 bytes as shown below.
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1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3 1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OPTION-CODE TBD | OPTION-LENGTH = 18 | | OPTION-CODE TBD | OPTION-LENGTH = 18 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Resolver Cookie upper half | | Resolver Cookie upper half |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Resolver Cookie lower half | | Resolver Cookie lower half |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Server Cookie upper half | | Server Cookie upper half |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Server Cookie lower half | | Server Cookie lower half |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Error Code | | Error Code |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The Resolver and Server Cookies are stored in network byte order and The Resolver and Server Cookies are stored in network byte order and
are determined as described below. are determined as described below.
The Error Code field MUST BE zero in requests and in responses unless The Error Code field MUST be zero in requests and in responses unless
the response is communicating a DNS cookie error. Three values are the response is communicating a DNS cookie error. Three values are
possible for Error Code: NOCOOKIE and BADCOOKIE which occur with a specified in this document for Error Code: NOCOOKIE and BADCOOKIE
Refused RCODE in the DNS response header, and MANYCOOKIE which occurs which occur with a Refused RCODE in the DNS response header, and
with a FormErr RCODE in the DNS header. More information on the MANYCOOKIE which occurs with a FormErr RCODE in the DNS header. More
generation of error response appears in Section 5 below. information on the generation of error response appears in Section 5
below.
4.1 Resolver Cookies 4.1 Resolver Cookies
The Resolver Cookie, when it occurs in an OPT in a DNS response, is The Resolver Cookie, when it occurs in an OPT in a DNS response, is
intended to weakly assure the resolver that the response came from a intended to weakly assure the resolver that the response came from a
server at the indicated source IP address. server at the indicated source IP address.
Servers remember the Resolver Cookie that appears in a query long Servers remember the Resolver Cookie that appears in a query long
enough to use it in the construction of the COOKIE OPT option in the enough to use it in the construction of the COOKIE OPT option in the
corresponding response if such a COOKIE OPT option is included in corresponding response if such a COOKIE OPT option is included in
that response. that response.
The Resolver Cookie SHOULD be a pseudo-random function of the server The Resolver Cookie SHOULD be a pseudo-random function of the server
IP address and a secret quantity known only to the resolver. This IP address and a secret quantity known only to the resolver. This
resolver secret SHOULD have 64 bits of entropy [RFC4086] and MAY be resolver secret SHOULD have 64 bits of entropy [RFC4086] and MAY be
changed periodically. The RECOMMENDED method is the HMAC-MD5-64
[RFC1321], [RFC2104] of the server IP address and the resolver
secret. That is
Resolver Cookie = INTERNET-DRAFT DNS Cookies
Truncate-64 ( HMAC-MD5 ( Server IP, Resolver Secret ) )
A resolver MUST NOT use the same Resolver Cookie value for queries to changed periodically. The RECOMMENDED method is the HMAC-SHA1-64
[RFC1321], [RFC2104] of the server IP address and the resolver
secret. That is
INTERNET-DRAFT DNS Cookies Resolver Cookie = Truncate-64
( HMAC-SHA1 ( Server IP Address, Resolver Secret ) )
all servers. where Truncate-64 takes the first 64 bits. A resolver MUST NOT use
the same Resolver Cookie value for queries to all servers.
4.2 Server Cookies 4.2 Server Cookies
The Server Cookie, when it occurs in a COOKIE OPT option in a query, The Server Cookie, when it occurs in a COOKIE OPT option in a query,
is intended to weakly assure the server that the query legitimately is intended to weakly assure the server that the query legitimately
came from a resolver at the indicated source IP address that is using came from a resolver at the indicated source IP address that is using
the indicated Resolver Cookie. that Resolver Cookie.
Resolvers learn Server Cookies and retain them as soft state Resolvers learn Server Cookies and retain them as soft state
associated with the server IP address. They learn them from the associated with the server IP address. They learn them from the
Server Cookie that appears in the COOKIE OPT option of a reply that Server Cookie that appears in the COOKIE OPT option of a reply that
also has the correct Resolver Cookie, even if that reply is an error also has the correct Resolver Cookie, even if that reply is an error
message. message.
The Server Cookie SHOULD be a pseudo-random function of the request The Server Cookie SHOULD be a pseudo-random function of the request
source IP address, the request Resolver Cookie, and a secret quantity source IP address, the request Resolver Cookie, and a secret quantity
known only to the server. This server secret SHOULD have 64 bits of known only to the server. This server secret SHOULD have 64 bits of
entropy [RFC4086] and SHOULD be changed periodically such as daily. entropy [RFC4086] and SHOULD be changed periodically such as daily.
The RECOMMENDED method is the HMAC-MD5-64 [RFC1321], [RFC2104] of the The RECOMMENDED method is the HMAC-SHA1-64 [RFC1321], [RFC2104] of
request IP address, the Resolver Cookie, and the server secret. That the request IP address, the Resolver Cookie, and the server secret.
is That is
Server Cookie = Truncate-64 ( Server Cookie = Truncate-64 ( HMAC-SHA1 (
HMAC-MD5 ( (Request IP | Resolver Cookie), Server Secret ) ) (Request IP Address | Resolver Cookie), Server Secret ) )
where "|" represents concatenation. where Truncate-64 takes the first 64 bits and "|" represents
concatenation.
A server MUST NOT use the same Server Cookie value for responses to A server MUST NOT use the same Server Cookie value for responses to
all requests. all resolvers.
5. General Policies and Implementation 5. DNS Cookie Policies and Implementation Requirements
DNS resolvers and servers will adopt one of various policies DNS resolvers and servers will adopt one of various policies
regarding cookies. These policies SHOULD be logically settable on a regarding cookies. These policies SHOULD be logically settable on a
per server IP address basis for resolvers and a per resolver ( IP per server IP address basis for resolvers and a per resolver ( IP
address, Resolver Cookie ) pair for servers. Thus a resolver can address, Resolver Cookie ) pair for servers. Thus a resolver can
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have different policies for different servers, based on the server IP have different policies for different servers, based on the server IP
address. And a server can have different policies for different address. And a server can have different policies for different
resolvers, based on the resolver IP address and Resolver Cookie. Of resolvers, based on the resolver IP address and Resolver Cookie. Of
course, the actual implementation of setting these policies may by course, the actual implementation of setting these policies may be
for blocks or classes of values or use sparse array techniques. for blocks or classes of values or use sparse array techniques.
The policy for each value is either "Disabled", "Enabled", or The policy for each value is either "Disabled", "Enabled", or
"Enforced" as described below. "Enforced" as described below.
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5.1 Resolver Policies and Implementation 5.1 Resolver Policies and Implementation
A resolver will logically have one of the following three policies
for each DNS server as distinguished by server IP Address.
Disabled: Disabled:
Never include a COOKIE RR in requests. Never include a COOKIE OPT option in requests.
Ignore COOKIE OPT options in responses. Ignore COOKIE OPT options in responses.
Enabled: Enabled:
Always include an OPT RR with a COOKIE option in requests. If a Always include a COOKIE OPT option in requests. If a cached Server
cached Server Cookie for the server is not available, the Cookie for the server is not available, the Server Cookie field
Server Cookie field can be set to any value. can be set to any value.
Normally process responses without a COOKIE OPT option. Normally process responses without a COOKIE OPT option.
Silently ignore responses with more than one COOKIE OPT option. Silently ignore responses with more than one COOKIE OPT option.
Silently ignore responses with one COOKIE OPT option if it has an Silently ignore responses with one COOKIE OPT option if it has an
incorrect Resolver Cookie value. incorrect Resolver Cookie value.
On receipt of a response with one COOKIE OPT option and it having On receipt of a response with one COOKIE OPT option and it having
the correct Resolver Cookie value (even if it is a BADCOOKIE the correct Resolver Cookie value (even if it is a BADCOOKIE
error response), perform normal response processing, including error response), perform normal response processing, including
caching the received Server Cookie and MUST change to the caching the received Server Cookie and MUST change to the
Enforced policy for DNS requests to that server IP address. Enforced policy for DNS requests to that DNS server IP address.
This policy change SHOULD be treated as soft state with the This policy change SHOULD be treated as soft state with the
same discard policy as the Server Cookie value for that server. same discard policy as the Server Cookie value for that server.
On discarding that state information, the policy for that On discarding that state information, the policy for that DNS
server reverts to Enabled. server reverts to Enabled.
Enforced: Enforced:
Always include a COOKIE OPT option in requests. Always include a COOKIE OPT option in requests.
Silently ignore all responses that do not include exactly one Silently ignore all responses that do not include exactly one
COOKIE OPT option with it having the correct Resolver Cookie COOKIE OPT option having the correct Resolver Cookie value.
value. Normally process responses which do include such a
COOKIE OPT option.
5.2 Server Policies and Implementation 5.2 Server Policies and Implementation
A server will logically have one of the following three policies for
each DNS resolver as distinguished by resolver IP Address and
Resolver Cookie.
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Disabled: Disabled:
Ignore COOKIE OPT options in requests. Ignore COOKIE OPT options in requests.
Never include a COOKIE OPT option in responses. Never include a COOKIE OPT option in responses.
Enabled: Enabled:
Always include a COOKIE OPT option in responses.
Normally process requests without a COOKIE OPT option. Normally process requests without a COOKIE OPT option.
Ignore, other than sending a MANYCOOKIE error response, any Ignore, other than sending a MANYCOOKIE error response, any
request with more than one COOKIE OPT option. request with more than one COOKIE OPT option.
Ignore, other than sending a BADCOOKIE error response, any query Ignore, other than sending a BADCOOKIE error response, any query
with one COOKIE OPT option if it has an incorrect Server with one COOKIE OPT option if it has an incorrect Server
Cookie. Cookie.
On receipt of a request with a COOKIE OPT option having the On receipt of a request with a COOKIE OPT option having the
correct Server Cookie value, perform normal request processing correct Server Cookie value, perform normal request processing
and SHOULD adopt the Enforced policy for DNS requests from that and SHOULD adopt the Enforced policy for DNS requests from that
resolver IP address with that Resolver Cookie in the request. resolver IP address with that Resolver Cookie in the request.
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This policy change for that resolver SHOULD be treated as soft This policy change for that resolver SHOULD be treated as soft
state. On discarding that state information, the policy for state. On discarding that state information, the policy for
that resolver IP and Resolver Cookie pair reverts to enabled. that resolver IP and Resolver Cookie pair reverts to enabled.
Always include a COOKIE OPT option in responses.
Enforced: Enforced:
Always include a COOKIE OPT option in responses.
Ignore requests without a COOKIE OPT option or with more than one Ignore requests without a COOKIE OPT option or with more than one
COOKIE OPT option, other than sending a NOCOOKIE or MANYCOOKIE COOKIE OPT option, other than sending a NOCOOKIE or MANYCOOKIE
error respectively. error respectively.
Ignore requests with one COOKIE OPT option if they have an Ignore requests with one COOKIE OPT option if they have an
incorrect Server Cookie, other than sending a BADCOOKIE error incorrect Server Cookie, other than sending a BADCOOKIE error
message. message.
If a request has one COOKIE OPT option with a correct Server If a request has one COOKIE OPT option with a correct Server
Cookie, perform normal processing of the request. Cookie, perform normal processing of the request.
Include a COOKIE OPT option in all responses.
5.3 Implementation Requirements 5.3 Implementation Requirements
DNS resolvers and servers MUST implement DNS cookies. DNS resolvers and servers SHOULD implement DNS cookies.
DNS resolvers SHOULD operate in and be shipped so as to default to DNS resolvers SHOULD operate in and be shipped so as to default to
the Enabled or Enforced mode for all servers. the Enabled or Enforced mode for all servers.
DNS servers SHOULD operate in and be shipped so as to default to the DNS servers SHOULD operate in and be shipped so as to default to the
Enabled or Enforced mode for all resolvers they are willing to Enabled or Enforced mode for all resolvers they are willing to
service. service.
6. NAT and AnyCast Considerations 6. NAT and AnyCast Considerations
[The section below is too confusing and needs to be reworded...]
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In the Classic Internet, DNS Cookies could simply be a pseudo-random In the Classic Internet, DNS Cookies could simply be a pseudo-random
function of the resolver IP address and a sever secret or the server function of the resolver IP address and a sever secret or the server
IP address and a resolver secret. You would want to compute the IP address and a resolver secret. You would want to compute the
Server Cookie that way, so a resolver could cache its Server Cookie Server Cookie that way, so a resolver could cache its Server Cookie
for a particular server for an indefinitely amount of time and the for a particular server for an indefinitely amount of time and the
server could easily regenerate and check it. You could consider the server could easily regenerate and check it. You could consider the
Resolver Cookie to be a resolver signature over the server IP address Resolver Cookie to be a resolver signature over the server IP address
which the resolver checks in responses and you could extend this which the resolver checks in responses and you could extend this
signature to cover the request ID, for example. signature to cover the request ID, for example.
But we have this wart called NAT [RFC3022], Network Address But we have this reality called NAT [RFC3022], Network Address
Translation (including therein for the purposes of this document NAT- Translation (including therein for the purposes of this document NAT-
PT [RFC2766], Network Address and Protocol Translation). There is no PT [RFC2766], Network Address and Protocol Translation). There is no
problem with DNS transactions between resolvers and servers behind a problem with DNS transactions between resolvers and servers behind a
NAT box using local IP addresses. Nor is there a problem with NAT NAT box using local IP addresses. Nor is there a problem with NAT
translation of internal addresses to external addresses or translation of internal addresses to external addresses or
translations between IPv4 and IPv6 addresses, as long as the address translations between IPv4 and IPv6 addresses, as long as the address
INTERNET-DRAFT DNS Cookies
mapping is relatively stable. Should an internal resolver being mapping is relatively stable. Should an internal resolver being
mapped to a particular external IP address change occasionally, the mapped to a particular external IP address change occasionally, the
disruption is no more than when a resolver rolls-over its DNS COOKIE disruption is no more than when a resolver rolls-over its DNS COOKIE
secret. And normally external access to a DNS server behind a NAT box secret. And normally external access to a DNS server behind a NAT box
is handled by a fixed mapping which forwards externally received DNS is handled by a fixed mapping which forwards externally received DNS
requests to a specific host. requests to a specific host.
However, NAT devices sometimes also map ports. This can cause However, NAT devices sometimes also map ports. This can cause
multiple DNS requests and responses from multiple internal hosts to multiple DNS requests and responses from multiple internal hosts to
be simultaneously mapped to a smaller number of external IP be simultaneously mapped to a smaller number of external IP
addresses, frequently one. There could be many resolvers behind a addresses, frequently one. There could be many resolvers behind a
NAT box that appear to come from the same source IP address to a NAT box that appear to come from the same source IP address to a
server outside that NAT box.. If one of these were an attacker server outside that NAT box.. If one of these were an attacker
(think Zombie or Botnet), that behind-NAT attacked could get the (think Zombie or Botnet), that behind-NAT attacker could get the
Server Cookie for some server for the outgoing IP address by just Server Cookie for some server for the outgoing IP address by just
making some random request to that server. It could then include that making some random request to that server. It could then include that
Server Cookie in the COOKIE RR of requests to the server with the Server Cookie in the COOKIE RR of requests to the server with the
forged IP address of the local IP address of some other host and/or forged IP address of the local IP address of some other host and/or
resolver behind the NAT box. (Attacker possession of this Server resolver behind the NAT box. (Attacker possession of this Server
Cookie will not help in forging responses to cause cache poisoning as Cookie will not help in forging responses to cause cache poisoning as
such responses are protected by the required Resolver Cookie.) such responses are protected by the required Resolver Cookie.)
To fix this potential defect, it is necessary to distinguish To fix this potential defect, it is necessary to distinguish
different resolvers behind a NAT box from the point of view of the different resolvers behind a NAT box from the point of view of the
server. It is for this reason that the Server Cookie is specified as server. It is for this reason that the Server Cookie is specified as
a pseudo-random function of both the request source IP address and a pseudo-random function of both the request source IP address and
the Resolver Cookie. From this inclusion of the Resolver Cookie in the Resolver Cookie. From this inclusion of the Resolver Cookie in
the calculation of the Server Cookie, it follows that a stable the calculation of the Server Cookie, it follows that a stable
Resolver Cookie, for any particular server, is needed. If, for Resolver Cookie, for any particular server, is needed. If, for
example, the request ID was included in the calculation of the example, the request ID was included in the calculation of the
Resolver Cookie, it would normally change with each query to a Resolver Cookie, it would normally change with each query to a
particular server. This would mean that each query would have to be particular server. This would mean that each query would have to be
sent twice: first to learn the new Server Cookie based on this new sent twice: first to learn the new Server Cookie based on this new
INTERNET-DRAFT DNS Cookies
Resolver Cookie based on the new ID and then again using this new Resolver Cookie based on the new ID and then again using this new
Resolver Cookie to actually get an answer. Thus the input to the Resolver Cookie to actually get an answer. Thus the input to the
Resolver Cookie computation must be limited to the server IP address Resolver Cookie computation must be limited to the server IP address
and one or more things that change slowly such as the resolver and one or more things that change slowly such as the resolver
secret. secret.
In principle, there could be a similar problem for servers, not In principle, there could be a similar problem for servers, not
particularly due to NAT but due to mechanisms like anycast which may particularly due to NAT but due to mechanisms like anycast which may
cause queries to a DNS server at an IP address to be delivered to any cause queries to a DNS server at an IP address to be delivered to any
one of several machines. (External queries to a DNS server behind a one of several machines. (External queries to a DNS server behind a
NAT box usually occur via port forwarding such that all such queries NAT box usually occur via port forwarding such that all such queries
go to one host.) However, it is impossible to solve this the way the go to one host.) However, it is impossible to solve this the way the
similar problem was solved for NATed resolvers; if the Server Cookie similar problem was solved for NATed resolvers; if the Server Cookie
was included in the calculation of the Resolver Cookie the same way was included in the calculation of the Resolver Cookie the same way
the Resolver Cookie is included in the Server Cookie, you would just the Resolver Cookie is included in the Server Cookie, you would just
get an almost infinite series of BADCOOKIE errors as a query was get an almost infinite series of BADCOOKIE errors as a query was
repeatedly retried. repeatedly retried.
INTERNET-DRAFT DNS Cookies
For server accessed via anycast or similar mechanisms to successfully For server accessed via anycast or similar mechanisms to successfully
support DNS COOKIES, the server clones must either all use the same support DNS COOKIES, the server clones must either all use the same
server secret or the mechanism that distributes queries to them must server secret or the mechanism that distributes queries to them must
cause the queries from a particular resolver to go to a particular cause the queries from a particular resolver to go to a particular
server for a sufficiently long period of time that extra queries due server for a sufficiently long period of time that extra queries due
to changes in Server Cookie resulting from accessing different server to changes in Server Cookie resulting from accessing different server
machines are not unduly burdensome. When such anycast accessed machines are not unduly burdensome. When such anycast accessed
servers act as recursive servers or otherwise act as resolvers they servers act as recursive servers or otherwise act as resolvers they
normally use a different unique address to source their queries and normally use a different unique address to source their queries and
avoid confusion in the delivery of responses. avoid confusion in the delivery of responses.
For simplicity, it is recommended that the same server secret be used For simplicity, it is RECOMMENDED that the same server secret be used
by each set of anycast servers. by each set of anycast servers.
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7. IANA Considerations 7. IANA Considerations
The OPT option value for COOKIE is TBD. IANA will allocate the following code points:
Three new RCODES are assigned values above 15: The OPT option value for COOKIE is <TBD>.
NOCOOKIE is assigned the value (TBD, 23 suggested).
BADCOOKIE is assigned the value (TBD, 24 suggested). Three new RCODES are assigned values as listed below:
MANYCOOKIE is assigned the value (TBD, 25 suggested). NOCOOKIE is assigned the value (<TBD>, 23 suggested).
BADCOOKIE is assigned the value (<TBD>, 24 suggested).
MANYCOOKIE is assigned the value (<TBD>, 25 suggested).
8. Security Considerations 8. Security Considerations
DNS Cookies provide a weak form of authentication of DNS requests and DNS Cookies provide a weak form of authentication of DNS requests and
responses. In particular, they provide no protection at all against responses. In particular, they provide no protection at all against
"on-path" adversaries; that is, they provide no protection against "on-path" adversaries; that is, they provide no protection against
any adversary which can observe the plain text DNS traffic, such as any adversary which can observe the plain text DNS traffic, such as
an on-path router, bridge, or any device on an on-path shared link an on-path router, bridge, or any device on an on-path shared link
(unless the DNS traffic in question on that path is appropriately (unless the DNS traffic in question on that path is appropriately
encrypted). encrypted).
For example, if a host is connected via an unsecured IEEE 802.11 link For example, if a host is connected via an unsecured IEEE 802.11 link
(Wi-Fi), any device in the vicinity that could receive and decode the (Wi-Fi), any device in the vicinity that could receive and decode the
802.11 transmissions must be considered "on-path". On the other hand, 802.11 transmissions must be considered "on-path". On the other hand,
in a similar situation but one where 802.11i security is in a similar situation but one where 802.11i security is
appropriately deployed on the Wi-Fi network nodes, only the Access appropriately deployed on the Wi-Fi network nodes, only the Access
Point via which the host is connecting is "on-path". Point via which the host is connecting is "on-path".
Despite these limitations, use of DNS Cookies on the global Internet Despite these limitations, use of DNS Cookies on the global Internet
are expected to provide a reduction in the available launch points is expected to provide a reduction in the available launch points for
for the traffic amplification and denial of service attacks described the traffic amplification and denial of service forgery attacks
in Section 2 above. described in Section 2 above.
The recommended cryptographic algorithm for use in DNS Cookies is
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HMAC-MD5-64, that is, the HMAC scheme [RFC2104] using the MD5 hash The recommended cryptographic algorithms for use in DNS Cookies is
function [RFC1321] with its output truncated to 64-bits. Although MD5 HMAC-SHA1-64, that is, the HMAC scheme [RFC2104] using the SHA1 hash
is now considered to be susceptible to collisions attacks, this does function [RFC3174] [RFC4634] with the HMAC output truncated to
not effect the security of HMAC-MD5. 64-bits. MD5 is now considered to be susceptible to collisions
attacks. Although this does not effect the security of HMAC-MD5,
HMAC-SHA1 is stronger.
In light of the weak plain-text token security provided by DNS In light of the weak plain-text token security provided by DNS
Cookies, stronger cryptography is probably not warranted. However, Cookies, stronger cryptography is probably not warranted and in many
there is nothing wrong with using, for example, HMAC-SHA256-64 cases it would be acceptable to use the weaker MD5 hash function
instead, assuming a DNS processor has adequate computational [RFC1321]. However, there is nothing wrong with using something
resources available. DNS processors that feel the need for somewhat stronger, for example, HMAC-SHA256-64 [RFC4634], assuming a DNS
stronger security without a significant increase in computational processor has adequate computational resources available. DNS
load should consider more frequent changes in their resolver and/or processors that feel the need for somewhat stronger security without
server secret; however, this does require more frequent generation of a significant increase in computational load should consider more
a cryptographically strong random number [RFC4086] and a change in a
server secret will result in a number of BADCOOKIE rejected requests
from resolvers caching their old Server Cookie.
9. Copyright and Disclaimer
Copyright (C) The Internet Society (2006).
This document is subject to the rights, licenses and restrictions INTERNET-DRAFT DNS Cookies
contained in BCP 78, and except as set forth therein, the authors
retain all their rights.
This document and the information contained herein are provided on an frequent changes in their resolver and/or server secret; however,
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS this does require more frequent generation of a cryptographically
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET strong random number [RFC4086] and a change in a server secret will
ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, result in a number of initial BADCOOKIE rejected requests from
INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE resolvers caching their old Server Cookie.
INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
10. Normative References 9. Normative References
[RFC1321] - Rivest, R., "The MD5 Message-Digest Algorithm", RFC 1321, [RFC1321] - Rivest, R., "The MD5 Message-Digest Algorithm", RFC 1321,
April 1992. April 1992.
[RFC2104] - Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed- [RFC2104] - Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed-
Hashing for Message Authentication", RFC 2104, February 1997. Hashing for Message Authentication", RFC 2104, February 1997.
[RFC2119] - Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] - Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997. Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2181] - Elz, R. and R. Bush, "Clarifications to the DNS [RFC2181] - Elz, R. and R. Bush, "Clarifications to the DNS
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Specification", RFC 2181, July 1997. Specification", RFC 2181, July 1997.
[RFC2671] - Vixie, P., "Extension Mechanisms for DNS (EDNS0)", August [RFC2671] - Vixie, P., "Extension Mechanisms for DNS (EDNS0)", August
1999. 1999.
[RFC4086] - Eastlake, D., 3rd, Schiller, J., and S. Crocker, [RFC4086] - Eastlake, D., 3rd, Schiller, J., and S. Crocker,
"Randomness Requirements for Security", BCP 106, RFC 4086, June 2005. "Randomness Requirements for Security", BCP 106, RFC 4086, June 2005.
[STD13] [STD13]
Mockapetris, P., "Domain names - concepts and facilities", STD Mockapetris, P., "Domain names - concepts and facilities", STD
13, RFC 1034, November 1987. 13, RFC 1034, November 1987.
Mockapetris, P., "Domain names - implementation and Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, November 1987. specification", STD 13, RFC 1035, November 1987.
11. Informative References. 10. Informative References
[RFC2766] - Tsirtsis, G., P. Srisuresh"Network Address Translation - [RFC2766] - Tsirtsis, G., P. Srisuresh, "Network Address Translation
Protocol Translation (NAT-PT)", February 2000. - Protocol Translation (NAT-PT)", February 2000.
[RFC2845] - Vixie, P., Gudmundsson, O., Eastlake 3rd, D., and B. [RFC2845] - Vixie, P., Gudmundsson, O., Eastlake 3rd, D., and B.
Wellington, "Secret Key Transaction Authentication for DNS (TSIG)", Wellington, "Secret Key Transaction Authentication for DNS (TSIG)",
RFC 2845, May 2000. RFC 2845, May 2000.
[RFC2930] - Eastlake 3rd, D., "Secret Key Establishment for DNS (TKEY [RFC2930] - Eastlake 3rd, D., "Secret Key Establishment for DNS (TKEY
RR)", RFC 2930, September 2000. RR)", RFC 2930, September 2000.
[RFC2931] - Eastlake 3rd, D., "DNS Request and Transaction Signatures [RFC2931] - Eastlake 3rd, D., "DNS Request and Transaction Signatures
INTERNET-DRAFT DNS Cookies
( SIG(0)s )", RFC 2931, September 2000. ( SIG(0)s )", RFC 2931, September 2000.
[RFC3022] - Srisuresh, P. and K. Egevang, "Traditional IP Network [RFC3022] - Srisuresh, P. and K. Egevang, "Traditional IP Network
Address Translator (Traditional NAT)", RFC 3022, January 2001. Address Translator (Traditional NAT)", RFC 3022, January 2001.
[RFC3174] - Eastlake 3rd, D. and P. Jones, "US Secure Hash Algorithm
1 (SHA1)", RFC 3174, September 2001.
[RFC4033] - Arends, R., Austein, R., Larson, M., Massey, D., and S. [RFC4033] - Arends, R., Austein, R., Larson, M., Massey, D., and S.
Rose, "DNS Security Introduction and Requirements", RFC 4033, March Rose, "DNS Security Introduction and Requirements", RFC 4033, March
2005. 2005.
[RFC4034] - Arends, R., Austein, R., Larson, M., Massey, D., and S. [RFC4034] - Arends, R., Austein, R., Larson, M., Massey, D., and S.
Rose, "Resource Records for the DNS Security Extensions", RFC 4034, Rose, "Resource Records for the DNS Security Extensions", RFC 4034,
March 2005. March 2005.
[RFC4035] - Arends, R., Austein, R., Larson, M., Massey, D., and S. [RFC4035] - Arends, R., Austein, R., Larson, M., Massey, D., and S.
Rose, "Protocol Modifications for the DNS Security Extensions", RFC Rose, "Protocol Modifications for the DNS Security Extensions", RFC
4035, March 2005. 4035, March 2005.
[RFC4634] - Eastlake, D. and T. Hansen, "US Secure Hash Algorithms
(SHA)", RFC 4634, July 2006.
INTERNET-DRAFT DNS Cookies INTERNET-DRAFT DNS Cookies
Author's Address Author's Address
Donald E. Eastlake 3rd Donald E. Eastlake 3rd
Motorola Laboratories Motorola Laboratories
111 Locke Drive 111 Locke Drive
Marlborough, MA 01752 USA Marlborough, MA 01752 USA
Telephone: +1-508-786-7554 (w) Telephone: +1-508-786-7554 (w)
EMail: Donald.Eastlake@motorola.com EMail: Donald.Eastlake@motorola.com
Copyright and Disclaimer
Copyright (C) The IETF Trust (2007).
This document is subject to the rights, licenses and restrictions
contained in BCP 78, and except as set forth therein, the authors
retain all their rights.
This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND
THE INTERNET ENGINEERING TASK FORCE DISCLAIM 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.
Additional IPR Provisions Additional IPR Provisions
The IETF takes no position regarding the validity or scope of any The IETF takes no position regarding the validity or scope of any
Intellectual Property Rights or other rights that might be claimed Intellectual Property Rights or other rights that might be claimed to
to pertain to the implementation or use of the technology pertain to the implementation or use of the technology described in
described in this document or the extent to which any license this document or the extent to which any license under such rights
under such rights might or might not be available; nor does it might or might not be available; nor does it represent that it has
represent that it has made any independent effort to identify any made any independent effort to identify any such rights. Information
such rights. Information on the procedures with respect to on the procedures with respect to rights in RFC documents can be
rights in RFC documents can be found in BCP 78 and BCP 79. found in BCP 78 and BCP 79.
Copies of IPR disclosures made to the IETF Secretariat and any Copies of IPR disclosures made to the IETF Secretariat and any
assurances of licenses to be made available, or the result of an assurances of licenses to be made available, or the result of an
attempt made to obtain a general license or permission for the use attempt made to obtain a general license or permission for the use of
of such proprietary rights by implementers or users of this such proprietary rights by implementers or users of this
specification can be obtained from the IETF on-line IPR repository specification can be obtained from the IETF on-line IPR repository at
at http://www.ietf.org/ipr. http://www.ietf.org/ipr.
The IETF invites any interested party to bring to its attention INTERNET-DRAFT DNS Cookies
any copyrights, patents or patent applications, or other
proprietary rights that may cover technology that may be required The IETF invites any interested party to bring to its attention any
to implement this standard. Please address the information to the copyrights, patents or patent applications, or other proprietary
IETF at ietf-ipr@ietf.org. rights that may cover technology that may be required to implement
this standard. Please address the information to the IETF at ietf-
ipr@ietf.org.
Expiration and File Name Expiration and File Name
This draft expires in April 2007. This draft expires in February 2008.
Its file name is draft-eastlake-dnsext-cookies-01.txt Its file name is draft-eastlake-dnsext-cookies-02.txt
 End of changes. 85 change blocks. 
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