One document matched: draft-livingood-dns-redirect-02.xml
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<rfc ipr='pre5378Trust200902' docName='draft-livingood-dns-redirect-02' category='info'>
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<!-- FRONT SECTION -->
<front>
<title abbrev='DNS Redirect Use by Service Providers'>
DNS Redirect Use by Service Providers
</title>
<!-- add role='editor' attribute to author tag below for the editors if appropriate -->
<author initials='T.' surname='Creighton' fullname='Tom Creighton'>
<organization abbrev='Comcast'>
Comcast Cable Communications
</organization>
<address>
<postal>
<street>One Comcast Center</street>
<street>1701 John F. Kennedy Boulevard</street>
<city>Philadelphia</city>
<region>PA</region>
<code>19103</code>
<country>US</country>
</postal>
<email>tom_creighton@cable.comcast.com</email>
<uri>http://www.comcast.com</uri>
</address>
<!-- author role='editor' is an optional value here -->
</author>
<author initials='C.' surname='Griffiths' fullname='Chris Griffiths'>
<organization abbrev='Comcast'>
Comcast Cable Communications
</organization>
<address>
<postal>
<street>One Comcast Center</street>
<street>1701 John F. Kennedy Boulevard</street>
<city>Philadelphia</city>
<region>PA</region>
<code>19103</code>
<country>US</country>
</postal>
<email>chris_griffiths@cable.comcast.com</email>
<uri>http://www.comcast.com</uri>
</address>
<!-- author role='editor' is an optional value here -->
</author>
<author initials='J.' surname='Livingood' fullname='Jason Livingood'>
<organization abbrev='Comcast'>
Comcast Cable Communications
</organization>
<address>
<postal>
<street>One Comcast Center</street>
<street>1701 John F. Kennedy Boulevard</street>
<city>Philadelphia</city>
<region>PA</region>
<code>19103</code>
<country>US</country>
</postal>
<email>jason_livingood@cable.comcast.com</email>
<uri>http://www.comcast.com</uri>
</address>
<!-- author role='editor' is an optional value here -->
</author>
<author initials='R.' surname='Weber' fullname='Ralf Weber'>
<organization abbrev='Unaffiliated'>
Unaffiliated
</organization>
<address>
<postal>
<street>Bleichgarten 1</street>
<region>Hohenahr-Hohensolms</region>
<code>35644 </code>
<country>Germany</country>
</postal>
<email>rw@hohensolms.de</email>
</address>
<!-- author role='editor' is an optional value here -->
</author>
<date day='6' month='September' year='2010'/>
<!-- META-DATA DECLARATIONS -->
<area></area>
<!-- WG name at the upperleft corner of the doc; 'Internet Engineering Task Force' is fine for individual submissions. -->
<workgroup>Internet Engineering Task Force</workgroup>
<abstract>
<t>The objective of this document is to describe the design of so-called DNS Redirect services deployed today by Internet Service Providers (ISPs), DNS Application Service Providers (ASPs), and other organizations providing so-called DNS Redirect services via their recursive DNS servers, as well as to describe the recommended practices regarding relating to DNS redirect. This document specifically and narrowly addresses those cases where DNS Redirect is being utilized to provide a web error redirect service to end users, and describes the critical implications for DNS Redirect when DNSSEC is deployed.</t>
</abstract>
<!-- END META-DATA DECLARATIONS -->
</front>
<!-- END FRONT SECTION -->
<!-- MIDDLE SECTION -->
<middle>
<section anchor='ReqLang' title='Requirements Language' toc='include'>
<t>The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in <xref target="RFC2119"/>.</t>
</section>
<section anchor='intro' title='Introduction' toc='include'>
<t>Internet users typically are provided with several IP addresses for recursive DNS servers, as described in Section 2.3 of <xref target="RFC1591"/>, by their respective ISPs, typically in an automated fashion via DHCP <xref target="RFC2131"/>. Some other users and organizations choose to use a different set of IP address for their DNS servers, which are hosted and managed by another organization, such as a DNS ASP. It is also the case that a number of users and organizations choose to operate their own DNS servers, though those use cases are outside of the scope of this document.</t>
<t>ISPs and DNS ASPs have over time created " enhanced " DNS services for their users, which often rely upon DNS Redirect functionality. These enhanced services, which are offered on an opt-in or opt-out basis, can perform a number of enhanced services for users, such as attempting to interpret web address errors when an invalid fully qualified domain name (FQDN, Section 5.1 of <xref target="RFC1035"/>) has been typed by a user.</t>
<t>This document describes the design and function of a DNS Redirect service, as well as recommended practices and practices to avoid. It also describes the critical implications for DNS Redirect when DNSSEC is adopted, in <xref target='DNSSEC Considerations Section'/>.</t>
</section>
<section title='Document Scope' toc='include'>
<t>This document focuses on the systems and practices of ISPs and DNS ASPs. All other use cases, such as when an Internet user or organization chooses to operate their own DNS servers is outside of the scope of this document.</t>
<t>There are several ways that such entities can provide users with these enhanced DNS services. In addition to methods which rely primarily upon a recursive DNS server, alternate methods include (a) interception and replacement of the error by a web browser client software, (b) interception and replacement of the error by a tool bar, plug-in, personal firewall security software or other web browser client add-on. These alternate methods, which rely upon various types of client software, are also outside of the scope of this document.</t>
<t>It is important to note that while these alternate methods are considered out of scope for this document, this should not be interpreted as a negative judgment of their suitability or applicability to the relevant problem space. Instead, these should simply be considered as alternate methods since, as with most any technical problem, there are a variety of valid methods for solving a problem.</t>
<t>Lastly, while <xref target='options'/> indicates that users must be able to opt into or out of DNS Redirect services, the reasons for why an ISP or DNS ASP may choose one or the other as the default are out of scope.</t>
</section>
<section title='DNSSEC Considerations and Implications' anchor='DNSSEC Considerations Section' toc='include'>
<t>DNS security extensions defined in <xref target='RFC4033'/>, <xref target='RFC4034'/>, and <xref target='RFC4035'/> use cryptographic digital signatures to provide origin authentication and integrity assurance for DNS data. This is done by creating signatures for DNS data on a DNS Security-Aware Name Server that can be used by DNS Security-Aware Resolvers to verify the answers.</t>
<t>DNSSEC is now in the process of being deployed on authoritative servers, now that the DNS root has been signed and several key Top Level Domains (TLDs) have been signed. DNSSEC is also starting to be adopted by service providers, which are now in the process of adding DNSSEC validation in DNS recursive resolvers.</t>
<t>It is critically important that service providers understand that adoption of DNSSEC is technically incompatible with DNS redirect. As such, in order to properly implement DNSSEC and maintain a valid chain of trust, DNS redirect MUST NOT be used any longer. Thus, once DNSSEC is in widespread use, this document should be considered historical. That being said, sections of this document concerning opt-in and opt-out practices may be useful for future reference in other, unrelated documents.</t>
</section>
<section title='Terminology' toc='include'>
<t>While these terms are generally well known, it is important to define them in the context of this document.</t>
<section title='Internet Service Provider (ISP)' toc='exclude'>
<t>An Internet Service Provider, which provides Internet services, including basic network connectivity. It is not germane to this document what the method of connection is, such as wired or wireless, what the speed of such a connection is, or what other services are included or available to users. It is, however, assumed that the ISP is providing recursive DNS services to their users and is in some manner providing users with the IP addresses of these DNS servers, whether via DHCP, static assignment by users, or some other method.</t>
</section>
<section title='DNS Application Service Provider (ASP)' toc='exclude'>
<t>A DNS Application Service Provider, which provides managed and/or hosted recursive DNS services (and possibly other DNS services) to their users. In the case of managed services, the DNS ASP may remotely manage the recursive DNS servers in a user's network. For a hosted recursive DNS service, these servers are typically located outside of the user's network and these hosted resources are shared across multiple users. In most instances, these are hosted services and users are manually configuring either their DHCP server or their individual computing devices with the IP addresses of the recursive DNS servers operated by their ASP.</t>
</section>
<section title='Internet User' toc='exclude'>
<t>An Internet user, which is generally a person using a computing device to connect to and make use of the Internet. Such users are typically connected at the edge of the network, though the method by which they connect to the Internet is not particularly relevant to this document.</t>
</section>
<section title='DNS Recursive Resolver' toc='exclude'>
<t>A DNS recursive resolver processes fully qualified domain name queries (FQDN, Section 5.1 of <xref target="RFC1035"/>) into IP addresses by finding the resource records in the authoritative DNS servers for the domain associated with the FQDN. The resource records are then cached on the recursive server for future requests until an expiration timer expires called time to live (TTL), as described in Section 5.2 of <xref target="RFC2181"/>. These servers are in most cases provided by ISPs for name resolution.</t>
</section>
<section title='Web Browser' toc='exclude'>
<t>Client software operated by the user locally on their computing device, such as Microsoft Internet Explorer, Mozilla Firefox, Apple Safari, Google Chrome, etc.</t>
</section>
<section title='Web Error Landing Server' toc='exclude'>
<t>The host that a user is directed to when the DNS Recursive Server receives a NXDOMAIN response. The contents of the web page that the web server sends the user varies widely across different ISPs and DNS ASPs. In some cases it is simply a more descriptive error that the user would otherwise receive, while in other cases it may include links to sites similar to the URL attempted and/or a search page, among many other possibilities.</t>
</section>
<section title='User Options Web Server' toc='exclude'>
<t>The web server that a user is directed to via a link on a page served by the Web Error Landing Server, the Malicious Domain Web Error Landing Server, from another system such as an account management system, or via direct access, which enables a user to control whether or not they are opted into or opted out of DNS Redirect services. This is described in additional detail in the <xref target='options'/> section.</t>
</section>
<section title='NXDOMAIN Response' toc='exclude'>
<t>In this document, an NXDOMAIN (nonexistent domain) response can be used interchangeably with an RCODE 3 response. The RCODE 3 response was first documented in see Section 4.1.1 of <xref target="RFC1035"/>). Subsequent RFCs introduced the term NXDOMAIN response, which is synonymous with RCODE 3 and tends to be used more frequently, as noted in Section 2.2 of <xref target="RFC2136"/>, Section 1 of <xref target="RFC2308"/>, and Section 5.4 of <xref target="RFC2535"/>.</t>
</section>
</section>
<section title='Web Error Redirect' toc='include'>
<t>A web error redirect service enables an ISP or ASP to provide a user, who is generally utilizing a web browser, with an improved user experience when an attempt to reach a nonexistent domain is made.</t>
<section title='Web Error Redirect Problem Statement' toc='exclude'>
<t>A user enters an incorrect URL into their web browser, such as http://www.example.invalid, where .invalid is a nonexistent Top Level Domain (TLD, see Section 2 of <xref target="RFC1591"/>). In such a case, a user would typically receive an error.</t>
</section>
<section title='Web Error Redirect Solution Description' toc='exclude'>
<t>When a recursive DNS server detects such a nonexistent domain error (NXDOMAIN, see Section 4.1.1 of <xref target="RFC1035"/>), the ISP or ASP can instead provide a IP address for a Web Error Landing Server that can present the user with a list of suggested destinations rather than simply an error page. This page must also provide the user with a link to a method of opting out in the future. See <xref target='DNS Redirect Response'/>, <xref target='Web Error Landing Server'/>, and <xref target='DNS Redirect and HTTP Flow'/> for examples below.</t>
</section>
<section title='Web Error Redirect Solution Considerations' toc='exclude'>
<t>It is important to note that this technology can directly impact non-web clients such as instant messaging, VPNs, FTP, email filters-related DNS queries. Thus, special exclusions may need to be made in order to prevent unintentional side effects. Design considerations for the Web Error Search and Malicious Site Protection services should include properly and promptly terminating non-HTTP connection requests. Only A and AAAA resource records should be redirected, all other resource record types must be answered as if there was no redirection.</t>
</section>
</section>
<section title='Opt-In or Opt-Out Mechanisms' toc='include' anchor='options'>
<t>ISPs and DNS ASPs MUST provide their users with a method to opt into (opt-in) or out (opt-out) of some or all DNS Redirect services. Opt-out and opt-in methods should be reliable and should take into consideration the <xref target='Practices to Avoid'/> section below. Whether such services are offered on an opt-in or opt-out basis depends on a range of factors which are outside of the scope of this document. The two different methods, opt-out and opt-in, are described below.</t>
<section title='Opt-Out' toc='exclude'>
<t>Opt-Out is used when the users are by default offered all or some DNS Redirect services. As a result, the user must take an action to disable some or all such services. This is typically performed via a User Options Web Server. Users that have chosen to opt-out should receive DNS responses which are indistinguishable from those responses provided by a DNS server with no DNS Redirect functionality. In addition, opt-out should be persistent in nature, which means that opt-out should be tied to a fixed credential or attribute of some type, such as an account identifier, billing identifier, or equipment identifier, which is not typically subject to change on a regular basis.</t>
</section>
<section title='Opt-In' toc='exclude'>
<t>Opt-In is used when the users are by default not offered any DNS Redirect services. As a result, the user must take an action to enable some or all such services. This is typically performed via a User Options Web Server.</t>
</section>
<section title='Automated Mechanisms and Reasonable Processing Times' toc='exclude'>
<t>Once a user has selected to opt-in or opt-out of DNS Redirect services, such changes should occur automatically, when this is technically possible, without requiring the user to manually change any settings on their computing device. Such changes should also occur within a reasonable period of time. In some cases, however, a user may be offered the ability to speed the period of time for these changes to take effect, such as by restarting the computing device or a piece of network equipment which connects them to their ISP's network, for example.</t>
<t>While an automated mechanism may be the easiest for users, since it requires no manual reconfiguration of their network settings, the authors also recognize that there may be extenuating circumstances where this is not achievable. In such cases, which may for example be due to the particular attributes of one or another ISP's network design, a fully automated mechanism may not be possible. Another example is where a user is switching from their ISP's DNS server IP addresses to those of a DNS ASP. As a result, a user in all of these cases, as well as other possible cases, must manually reconfigure their network with different DNS IP addresses.</t>
</section>
<section title='Type of Opt-Out Method' toc='exclude'>
<t>There are several workable methods that can be employed to effect the actual opt-out for a given user. These include setting a local user application attribute, such as via a cookie in a web browser, as well as setting a network attribute, via a DHCP change or manually configuring the DNS IP addresses (in the operating system, modem, home gateway device, or router) in order to change the DNS IP addresses for a particular user.</t>
<t>While all of these methods are workable and can be made reliable, the best current method is via a network-based change of some sort. In this way, all Internet-connected computing devices within a given household are included in the opt-out (these devices are generally connected in some manner to the LAN side of some type of customer premise device, such as a cable modem or DSL modem). This is in contrast to a method which uses a local user application attribute, such as a cookie in a web browser, where deletion of cookies, upgrade to a new operating system, upgrade to a new web browser, use of a different web browser, or countless other factors on that device could cause the user to be opted back into a DNS Redirect service. Thus, a network-based approach which sets opt-out-related attributes at the device, or household level, is the most inclusive and persistent method for providing a reliable opt-out method, and is the recommended practice.</t>
</section>
</section>
<section title='Practices to Avoid' toc='include' anchor='Practices to Avoid'>
<t>This document primarily focuses on the recommended practices for an ISP or ASP to provide users with DNS Redirect services. However, it is important to note that some entities may not operate in accordance with such practices. As such, some of these are catalogued below in order to contrast them with recommended practices and provide information which may be of interest and use to the community.</t>
<section title='Use of DNS Redirect with DNSSEC' toc='exclude'>
<t>When DNSSEC has been implemented in a service provider's resolvers, DNS redirect MUST NOT be used, as it is technically incompatible with DNSSEC and breaks the chain of trust critical to proper DNSSEC validation functionality.</t>
</section>
<section title='Improper Redirect of Valid Responses' toc='exclude'>
<t>It has been observed that some service providers improperly utilize DNS Redirect services when there is a valid DNS resource record returned in response to a DNS recursive query. The effect is to redirect users to a server not maintained by the intended destination, such as a web site that looks like the intended web site but is not actually the intended site and is instead controlled by the service provider. For example a DNS query for www.example.com results in a valid A record response, but this valid response is instead replaced with an A record controlled by the service provider. In this case the intended server identified with the valid A record contained valid, lawful, non-malicious content, and there would otherwise appear to be no valid justification for a redirect to occur. See <xref target='Improper Redirect of Valid Response Redirect and HTTP Flow'/> for an example below.</t>
<t>If there is a valid and reasonable justification for such a redirect to occur, examples of which are not currently known by the authors of this document, then the resulting connection to the server that the user has been redirected to should clearly and prominently disclose that this is not the intended site. For example, in the case of an attempt by a user to connect to a web site, the site may contain a banner or frame which indicates that this is not the intended site or that the site is in some manner controlled by the service provider. In addition, such a notice should also offer a clear method to opt-out of this redirect function.</t>
<t>Thus, to summarize, redirection of valid responses SHOULD NOT be performed.</t>
</section>
<section title='Redirect of SERVFAIL Responses' toc='exclude'>
<t>Redirection of SERVFAIL responses SHOULD NOT occur. SERVFAIL responses may occur intermittently in an operational network for a variety of highly transient reasons. As a result, a DNS Redirect should not be performed when a SERVFAIL response is received, as normal retry a short time later is likely to result in a valid response.</t>
</section>
<section title='Routinely Broken, Purposefully Broken, and Otherwise Unreliable Opt-Out Mechanisms' toc='exclude'>
<t>There are several well known and dependable methods of opt-out mechanisms that ISPs and DNS ASPs can deploy for users to opt-out of their DNS Redirect services. These methods can rather easily be employed and are highly recommended, as noted in <xref target='options'/>. However, some ISPs and DNS ASPs may instead choose to employ a less dependable mechanism, which routinely fails to work as expected by users or is known not to function properly.</t>
<t>For example, one routinely unreliable method for opt-out is the cookie-based method. When a user opts out of a DNS Redirect service, a cookie is installed in their web browser. The problem with this method occurs when a user clears their cookies or the cookies are deleted for some reason. In some cases, users may configure their web browsers to clear all cookies every time the close their web browser. Thus, one possible effect upon the user in this case is that they are once again opted into the redirect service. Furthermore, a cookie-based method has the effect of only opting out browser-based protocols (generally HTTP and HTTPS), which means that the user may have non-web applications affected by DNS Redirect, even though they believe they have opted-out. As a result, there is no assured permanency with this opt-out method, nor does it work consistently across all applications and protocols, which can be aggravating to users who do not wish to utilize DNS Redirect services.</t>
<t>Another example of an unreliable method for opt-out is one where opt-out is tied to the IP address of the user, where that address may be subject to change on a regular basis, such as via an ISP-based DHCP lease. In such a case, if opt-out was tied to what can be considered a largely dynamic IP address, then the user would be opted-in every time they received a new IP address, forcing them to repeatedly opt-out.</t>
<t>Thus, to summarize, the opt-out mechanism provided to users SHOULD be reliable and SHOULD NOT be routinely broken, purposefully broken, or otherwise unreliable.</t>
</section>
<section title='Markedly Slower DNS Query Performance' toc='exclude'>
<t>An ISP or DNS ASP should also understand that DNS query latency, the time between when a user's stub resolver issues a DNS query and receives a DNS response, should be kept as low as is reasonably possible. High DNS query latency is often perceived by users, and can have an adverse effect on a variety of applications where low DNS query latency may be especially important. Any additional processing which must be performed in order to provide DNS Redirect services should be monitored closely, in order that DNS Redirect functionality does not markedly slow DNS query performance.</t>
<t>Thus, to summarize, when DNS redirect is performed, DNS query performance SHOULD NOT suffer as a result, since this could provide an incrementally inferior user experience as compared to when DNS redirect is not performed.</t>
</section>
<section title='Override of a User's DNS Selection' toc='exclude'>
<t>Some users may decide to use the DNS server IP addresses of a DNS ASP or other non-ISP-provided DNS servers. Such selections should be preserved as the free choice of a user, particularly when DNS Redirect services are offered. Thus, an ISP SHOULD NOT redirect port 53 DNS traffic from servers intended by the user via their selection of non-ISP DNS servers to the DNS servers of the ISP, except in reasonable and justifiable cases where a user has been placed into a so-called "walled garden" for reasons of abuse, security compromise, account non-payment, new service activation, etc.</t>
</section>
</section>
<section title='Functional Design' toc='include'>
<t>The functional design described in this section is intended to be generally representative of the many different ways that DNS Redirect services are deployed today. As such, they are necessarily high level and different implementations may vary somewhat, due to any number of factors.</t>
<section title='DNS Recursive Resolver'>
<t>The DNS Recursive Resolver is used by the host computer to translate fully qualified domain names into IP addresses, according to Section 3.6.1 of <xref target="RFC1034"/>. When a FQDN does not exist in authoritative DNS a NXDOMAIN response, as described in Section 4.1.1 of <xref target="RFC1035"/> is normally returned (see <xref target='DNS Redirect Response'/>). In the case of DNS Redirect, the NXDOMAIN response is changed to reply with a resource record (RR) response which instructs the host computer to send the original request to a new IP address (see <xref target='DNS Redirect Response'/>).</t>
<figure anchor='DNS Redirect Response' title='DNS Redirect Response'>
<artwork><![CDATA[
Request Request
www.example.invalid www.example.invalid
+--------+ +--------+
++--++ ------------> | | ------------> | |
|| || | | | |
+-++--++-+ | | | |
+--------+ <------------ | | <------------ | |
Host NXDOMAIN +--------+ NXDOMAIN +--------+
Computer Response Recursive Response Authoritative
Server Server
]]></artwork></figure>
</section>
<section title='Web Error Landing Server'>
<t>When a user requests an invalid URL or Domain, their web client is redirected to a Web Error Landing Server which presents several possible helpful website views (see <xref target='Web Error Landing Server'/>). The first is "Did you mean..." response which presents the user with possible correct results based on their original invalid request. The search server can also present search engine results to the user.</t>
<figure anchor='Web Error Landing Server' title='Web Error Landing Server'>
<artwork><![CDATA[
Request Request
www.example.invalid www.example.invalid
+--------+ +--------+
++--++ ---------------> | | --------------->| |
|| || | | | |
+-++--++-+ | | | |
+--------+ <-------------- | | <------------- | |
Host Redirect +--------+ NXDOMAIN +--------+
Computer IP Address Recursive Response Authoritative
Server Server
|
| ___________________________________
| +--------+ | Web Response: |
| | | | "Did you mean...www.example.com"|
+------> | | ------> |__________________________________|
| | | Search result: #1 |
| | | Search result: #2 |
+--------+ |__________________________________|
Web Server
Landing Page
]]></artwork></figure>
</section>
<section title='Web Browser Client'>
<t>The Web Browser Client is redirected to a Web Server Landing Page instead of presenting an error page when there is no valid DNS record present.</t>
<t>Examples of common Web Browser Clients include:
<list style='symbols'>
<t>Microsoft Internet Explorer</t>
<t>Mozilla Firefox</t>
<t>Apple Safari</t>
<t>Google Chrome</t>
<t>Opera</t>
</list>
</t>
</section>
<section title='Domain White List'>
<t>There may be certain domains which should be not be redirected under any circumstances for technical, legal, business, or other reasons. The Domain White List can contain both domains, such as *.example.com, as well as specific FQDNs, such as www.example.com. For instance, the owner of example.com may request that the ISP or DNS ASP not perform DNS Redirect for the example.com domain, so that there is no DNS Redirect resulting from queries to nonexistent names, such as invalid.example.com.</t>
</section>
</section>
<section title='Example DNS and HTTP Flows' toc='include'>
<t>This section shows several illustrated examples of DNS and HTTP flows, in order to better explain certain DNS and HTTP use cases.</t>
<section title='Successful DNS Lookup and HTTP Flow' toc='exclude'>
<t>This example represents a successful lookup of a valid DNS RR, and the resulting HTTP transaction.</t>
<figure anchor='Successful DNS Lookup and HTTP Flow' title='Successful DNS Lookup and HTTP Flow'>
<artwork><![CDATA[
Web DNS R DNS A DNS Web Server
Browser Client Server Server 10.1.10.10
| Request | A | | |
|www.example. |Record Query | A | |
| com |www.example. |Record Query | |
|------------>| com |www.example. | |
| |------------>| com | |
| | |------------>| |
| | | A Record | |
| | A Record | 10.1.10.10 | |
| DNS Response| 10.1.10.10 |<------------| |
| 10.1.10.10 |<------------| | |
|<------------| | | |
| HTTP GET | | | |
| 10.1.10.10 | | | |
|------------------------------------------------------>|
| | | | |
| | | | |
| | | | |
]]></artwork></figure>
</section>
<section title='Unsuccessful DNS Lookup and HTTP Flow' toc='exclude'>
<t>This example represents a lookup of a nonexistent DNS RR, and the resulting HTTP transaction.</t>
<figure anchor='Unsuccessful DNS Lookup and HTTP Flow' title='Unsuccessful DNS Lookup and HTTP Flow'>
<artwork><![CDATA[
Web DNS R DNS A DNS
Browser Client Server Server
| Request | A | |
|www.example. |Record Query | A |
| invalid |www.example. |Record Query |
|------------>| invalid |www.example. |
| |------------>| invalid |
| | |------------>|
| | | NXDOMAIN |
| | NXDOMAIN |<------------|
| NXDOMAIN |<------------| |
|<------------| | |
| | | |
]]></artwork></figure>
</section>
<section title='DNS Redirect and HTTP Flow' toc='exclude'>
<t>This example represents a lookup of a non-existing DNS RR, and the HTTP transition that results from a typical DNS Redirect service.</t>
<figure anchor='DNS Redirect and HTTP Flow' title='DNS Redirect and HTTP Flow'>
<artwork><![CDATA[
Redirect
Host R DNS A DNS Web Server Web Server
Computer Server Server 10.2.20.20 10.1.10.10
| A | | | |
|Record Query | A | | |
|www.example. |Record Query | | |
| invalid |www.example. | | |
|------------>| invalid | | |
| |------------>| | |
| A Record | NXDOMAIN | | |
| 10.2.20.20 |<------------| | |
|<------------| | | |
| HTTP GET | | | |
| 10.2.20.20 | | | |
|---------------------------------------->| |
| | | HTTP 200 OK | |
|<----------------------------------------| |
| A | | | |
|Record Query | A | | |
|www.example. |Record Query | | |
| com |www.example. | | |
|------------>| com | | |
| |------------>| | |
| | A Record | | |
| A Record | 10.1.10.10 | | |
| 10.1.10.10 |<------------| | |
|<------------| | | |
| HTTP GET | | | |
| 10.1.10.10 | | | |
|------------------------------------------------------>|
| | | | HTTP 200 OK |
|<------------------------------------------------------|
| | | | |
]]></artwork></figure>
</section>
<section title='Improper Redirect of Valid Response Redirect and HTTP Flow' anchor='Improper Redirect Section' toc='exclude'>
<t>This example represents an improper redirect occurring when a valid DNS RR should have been returned in response to a DNS recursive query for an example website, the resulting HTTP transaction, and that no DNS query or HTTP traffic was sent to the valid authoritative DNS server and valid web server. <xref target='DNSSEC Considerations Section'/> shows one of the reasons why this practice is problematic. Another reason is that a user intends to visit a valid resource with lawful and legitimate content, such as a web site, and is instead sent to a different destination (which may even closely resemble the intended site, in the pattern used by phishing sites).</t>
<figure anchor='Improper Redirect of Valid Response Redirect and HTTP Flow' title='Improper Redirect of Valid Response Redirect and HTTP Flow'>
<artwork><![CDATA[
R DNS Improper Valid
Server Redirect Valid Web
Host R DNS Improper Web Server A DNS Server
Computer Server Reirect List 10.2.20.20 Server 10.1.10.10
| A | Improper | | | |
|Record Query |Redirect List| | | |
|www.example. | Query | | | |
| com |www.example. | | | |
|------------>| com | | | |
| |------------>| | | |
| | Postivie | | | |
| A Record | Match | | | |
| 10.2.20.20 |<------------| | | |
|<------------| | | | |
| HTTP GET | | | | |
| 10.2.20.20 | | | | |
|-------------------------------------->| | |
| | |HTTP 200 OK| | |
|<--------------------------------------| | |
| | | | | |
]]></artwork></figure>
</section>
</section>
<section title='Security Considerations' toc='include'>
<t>The critical considerations relating to DNS Security Extensions are detailed in <xref target='DNSSEC Considerations Section'/>.</t>
<t>Security best practices should be followed regarding access to the opt-in and opt-out functions, in order that someone other than the user is able to change the user's DNS Redirect settings. For example, the User Options Web Server must not permit someone to modify a page URI to access and change another user's options. Thus, if the URI is "http://www.example.net/redirect-options.php?account=1234", someone must not be able to modify the account to be "=1235" and then be able to change the options for a different user with some other additional validation being performed. While web site security practices are outside the scope of this document, the authors believe it is important to identify such problematic use cases to any ISPs and DNS ASPs offering and/or implementing DNS Redirect functionality.</t>
</section>
<section title='IANA Considerations' toc='include'>
<t>There are no IANA considerations in this document.</t>
</section>
<section title='Contributors' toc='include'>
<t>The following people made significant textual contributions to this document and played an important role in the development and evolution of this document:</t>
<t>Don Bowman, Sandvine (don@sandvine.com)</t>
<t>Rick Hiester, Verizon (richard.hiester@verizon.com)</t>
<t>Chris Roosenraad, Time Warner Cable (chris.roosenraad@twcable.com)</t>
<t>David Ulevitch, OpenDNS (david@opendns.com)</t>
</section>
<section title='Acknowledgements' toc='include'>
<t>The authors and contributors also wish to acknowledge the assistance of the following individuals in helping us to develop and/or review this document: </t>
<t>John Barnitz, Comcast Cable Communications (john_barnitz@cable.comcast.com)</t>
<t>Mike Burns, Cablevision (mburns@cablevision.com)</t>
<t>Phil Marcella, Comcast Interactive Media (phillip_marcella@cable.comcast.com)</t>
<t>Luis Uribarri, Comcast Cable Communications (luis_uribarri@cable.comcast.com)</t>
<t>Sandy Wilbourn, Nominum (sandy.wilbourn@nominum.com)</t>
<t>Matt Williams, Cox Cable (matt.williams@cox.com)</t>
<t>The authors and contributors also wish to thank ICANN's Security and Stability Advisory Committee (SSAC) for their review and debate of this document, as well as for raising important questions concerning DNSSEC compatibility.</t>
</section>
<!-- appendix -->
</middle>
<!-- END MIDDLE SECTION -->
<!-- BACK SECTION -->
<back>
<references title='Normative References'>
&RFC2119;
&RFC1034;
&RFC1035;
&RFC1536;
&RFC1591;
&RFC2131;
&RFC2136;
&RFC2181;
&RFC2308;
&RFC2535;
&RFC4033;
&RFC4034;
&RFC4035;
</references>
<section title='Document Change Log'>
<t>[RFC Editor: This section is to be removed before publication]</t>
<t>-02: Fixed some small grammatical nits.</t>
<t>-01: Removed sections regarding malicious domain protection, legally-mandated redirect, and content-based redirect based on DNSOP WG feedback to split those out into separate documents which will be published in the future. Also significantly modified the DNSSEC section and moved it to the top of the document. Also, capitalized applicable 2119 language.</t>
<t>-00: First version published.</t>
</section>
<section title='Open Issues'>
<t>[RFC Editor: This section is to be removed before publication]</t>
<t>
<list style='numbers'>
<t>RW: Consider whether it is a good idea to add to section 4.9 (NXDOMAIN RESPONSE) a reference to Authenticated Denial of Existence described in RFC4035 section 5.4 as these should be also redirected.</t>
<t>MB: Consider addressing how opt-out works when a user roams across a shared WiFi AP.</t>
<t>RH: Update reference to RFC2535, which is obsoleted by RFCs 4033, 4034, 4035.</t>
</list>
</t>
</section>
</back>
<!-- END BACK SECTION -->
</rfc>
<!-- FOR REFERENCE -->
<!-- less than is < -->
<!-- ampersand is & -->
<!-- apostrophe is &apos -->
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