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  • not require the use of the DNS protocol although it is expected to be the typical usage The previous paragraph only illustrates how DNS URIs are resolved using the DNS protocol A client MAY want to check that it understands the dnsclassval and dnstypeval before sending a query so that it will be able to understand the response However a typical example of a client that would not need to check dnsclassval and dnstypeval would be a proxy that would just treat the received answer as opaque data Character encoding considerations Characters are encoded as per RFC 3986 5 The DNS protocol does not consider character sets it simply transports opaque data In particular the dnsname field of the DNS URI is to be considered an internationalized domain name IDN unaware domain name slot in the terminology of RFC3940 14 The considerations for host and port are discussed in 5 Josefsson Expires February 2 2006 Page 6 Internet Draft DNS URI August 2005 Because is used as the DNS label separator an escaping mechanism is required to encode a that is part of a DNS label The escaping mechanism is described in section 5 1 of RFC 1035 2 For example a DNS label of exa mple can be escaped as exa mple or exa 046mple However the URI specification disallows the character from occurring directly in URIs so it must be escaped as 5c The single DNS label exa mple is thus encoded as exa 5c mple The same mechanism can be used to encode other characters for example and Note that and 2e are equivalent within dnsname and are interchangeable This URI specification allows all possible domain names to be encoded provided the encoding rules are observed per 5 However certain applications may restrict the set of valid characters Care should be taken so that invalid characters in these contexts do not cause harm In particular host names in the DNS have certain restrictions It is up to these applications to limit this subset this URI scheme places no restrictions Intended usage Whenever it is useful for DNS resources to be referenced by protocol independent identifiers Often this occurs when the data is more important than the access method Since software in general has coped without this so far it is not anticipated to be implemented widely nor migrated to by existing systems but specific solutions especially security related may find this appropriate Applications and or protocols that use this scheme include Security related software DNS administration tools and network programming packages Interoperability considerations The data referenced by this URI scheme might be transferred by protocols that are not URI aware such as the DNS protocol This is not anticipated to have any serious interoperability impact Interoperability problems may occur if one entity understands a new DNS class type mnemonic that another entity does not This is an interoperability problem for DNS software in general although it is not a major practical problem for current DNS deployments as the DNS types and classes are fairly static To guarantee interoperability implementations can use integers for all mnemonics not defined in 2 Interaction with Binary Labels 10 or other extended label types has not been analyzed However binary labels appear to be infrequently used in practice Josefsson Expires February 2 2006 Page 7 Internet Draft DNS URI August 2005 Contact simon josefsson org Author Change Controller simon josefsson org 4 Examples A DNS URI is of the following general form This is intended to illustrate not define the scheme dns authority domain CLASS class TYPE type The following illustrates a URI for a resource with the absolute name www example org the Internet IN class and the Address A type dns www example org clAsS IN tYpE A Since the default class is IN and the default type is A the same resource can be identified by a shorter URI using a relative name dns www example org The following illustrates a URI for a resource with the name simon example org for the CERT type in the Internet IN class dns simon example org type CERT The following illustrates a URI for a resource with the name ftp example org in the Internet IN class and the address A type but from the DNS authority 192 168 1 1 instead of the default authority dns 192 168 1 1 ftp example org type A The following illustrates various escaping techniques The owner name would be world wide web example domain org where denotes the character as part of a label and denotes the label separator dns world 20wide 20web example 5c domain org TYPE TXT The following illustrates a strange but valid DNS resource dns fw example org 20 00 example type TXT Josefsson Expires February 2 2006 Page 8 Internet Draft DNS URI August 2005 5 Acknowledgements Thanks to Stuart Cheshire Donald Eastlake Pasi Eronen Bill Fenner Ted Hardie Russ Housley Peter Koch Andrew Main Larry Masinter Michael Mealling Steve Mattson Marcos Sanz Jason Sloderbeck Paul Vixie Sam Weiler and Bert Wijnen for comments and suggestions The author acknowledges RSA Laboratories for supporting the work that led to this document 6 Security Considerations If a DNS URI references domains in the Internet DNS environment both the URI itself and the information referenced by the URI is public information If a DNS URI is used within an internal DNS environment both the DNS URI and the data referenced should be handled using the same considerations that apply to DNS data in the internal environment If information referenced by DNS URIs are used to make security decisions such data includes but is not limited to certificates stored in the DNS 9 implementations may need to employ security techniques such as Secure DNS 16 CMS 13 or OpenPGP 8 to protect the data during transport How to implement this will depend on the usage scenario and it is not up to this URI scheme to define how the data referenced by

    Original URL path: http://www.josefsson.org/dns-url/draft-josefsson-dns-url.txt (2016-04-30)
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  • Diff: draft-josefsson-dns-url-13.txt - draft-josefsson-dns-url.txt
    Note further that an empty Note further that an empty dnsname value is to be dnsname value is to be interpreted as the root itself interpreted as the root itself See below on relative dnsname s See below on relative dnsnames dnsquery dnsqueryelement dnsquery dnsquery dnsqueryelement dnsquery dnsqueryelement CLASS dnsclassval TYPE dnstypeval dnsqueryelement CLASS dnsclassval TYPE dnstypeval Each clause MUST NOT be used more Each clause MUST NOT be used more than once than once dnsclassval 1 digit IN CH dnsclassval 1 digit IN CH Any IANA registered DNS class mnemonic Any IANA registered DNS class mnemonic dnstypeval 1 digit A NS MD dnstypeval 1 digit A NS MD Any IANA registered DNS type mnemonic Any IANA registered DNS type mnemonic Unless specified in the URI the authority dnsauthority is Unless specified in the URI the authority dnsauthority is assumed to be locally known the class dnsclassval to be the assumed to be locally known the class dnsclassval to be the Internet class IN and the type dnstypeval to be the Address Internet class IN and the type dnstypeval to be the Address type A These default values match the typical use of DNS to type A These default values match the typical use of DNS to look up addresses for host names look up addresses for host names A dnsquery element MUST NOT contain more than one occur a nce of the A dnsquery element MUST NOT contain more than one occur re nce of the CLASS and TYPE fields For example both dns CLASS and TYPE fields For example both dns example TYPE A TYPE TXT and dns example TYPE A TYPE A are invalid example TYPE A TYPE TXT and dns example TYPE A TYPE A are invalid However the fields may occur in any order so that both dns However the fields may occur in any order so that both dns example TYPE A CLASS IN and dns example CLASS IN TYPE A are valid example TYPE A CLASS IN and dns example CLASS IN TYPE A are valid The digit representation of types and classes MAY be used when a The digit representation of types and classes MAY be used when a mnemonic for the corresponding value is not well known e g for mnemonic for the corresponding value is not well known e g for newly introduced types or classes but SHOULD NOT be used for the newly introduced types or classes but SHOULD NOT be used for the types or classes defined in the DNS specification 2 All types or classes defined in the DNS specification 2 All implementations MUST recognize the mnemonics defined in 2 implementations MUST recognize the mnemonics defined in 2 To avoid ambiguity relative dnsname values i e those not ending To avoid ambiguity relative dnsname values i e those not ending with are assumed to be relative to the root For example dns with are assumed to be relative to the root For example dns host example and dns host example both refer to the same owner host example and dns host example both refer to the same owner name namely host example Further an empty dnsname value is name namely host example Further an empty dnsname value is considered to be a degenerative form of a relative name which refer considered to be a degenerative form of a relative name which refer s to the root to the root To resolve a DNS URI using the DNS protocol 2 a query is created To resolve a DNS URI using the DNS protocol 2 a query is created using as input the dnsname dnsclassval and dnstypeval from the URI using as input the dnsname dnsclassval and dnstypeval from the URI string or the appropriate default values If an authority string or the appropriate default values If an authority dnsauthority is given in the URI string this indicate the server dnsauthority is given in the URI string this indicates the that should receive the DNS query otherwise the default DNS server server that should receive the DNS query Otherwise the default DNS should receive it server should receive it Note that DNS URIs could be resolved by other protocols than the DNS Note that DNS URIs could be resolved by other protocols than the DNS protocol or by using the DNS protocol in some other way than as protocol or by using the DNS protocol in some other way than as described above e g multicast DNS DNS URIs do not require the described above e g multicast DNS DNS URIs do not require the use of the DNS protocol although it is expected to be the typical use of the DNS protocol although it is expected to be the typical usage The previous paragraph only illustrate how DNS URIs are usage The previous paragraph only illustrate s how DNS URIs are resolved using the DNS protocol resolved using the DNS protocol A client MAY want to check that it understands the dnsclassval and A client MAY want to check that it understands the dnsclassval and dnstypeval before sending a query so that it will be able to dnstypeval before sending a query so that it will be able to understand the response However a typical example of a client that understand the response However a typical example of a client that would not need to check dnsclassval and dnstypeval would be a proxy would not need to check dnsclassval and dnstypeval would be a proxy that would just treat the received answer as opaque data that would just treat the received answer as opaque data Character encoding considerations The characters are encoded as per Character encoding considerations Characters are encoded as per RFC RFC 3986 5 The DNS protocol do not consider character sets it 3986 5 The DNS protocol does not consider character sets it simply transports opaque data In particular the dnsname field of simply transports opaque data In particular the dnsname field of the DNS URI is to be considered an internationalized domain name the DNS URI is to be considered an internationalized domain name IDN unaware domain name slot in the terminology of 16 The IDN unaware domain name slot in the terminology of RFC3940 14 considerations for host and port are discussed in 5 The considerations for host and port are discussed in 5 Because is used as the DNS label separator an escaping mechanism Because is used as the DNS label separator an escaping mechanism is required to encode a that is part of a DNS label The is required to encode a that is part of a DNS label The escaping mechanism is described in section 5 1 of RFC 1035 For escaping mechanism is described in section 5 1 of RFC 1035 2 For example a DNS label of exa mple can be escaped as exa mple or example a DNS label of exa mple can be escaped as exa mple or exa 046mple However the URI specification disallow the exa 046mple However the URI specification disallows the character from occuring directly in URIs so it must be escaped as character from occurring directly in URIs so it must be escaped as 5c The single DNS label exa mple is thus encoded as exa 5c The single DNS label exa mple is thus encoded as exa 5c mple The same mechanism can be used to encode other characters 5c mple The same mechanism can be used to encode other characters for example and Note that and 2e are equivalent for example and Note that and 2e are equivalent within dnsname and are interchangable within dnsname and are interchang e able This URI specification allows all possible domain names to be encoded This URI specification allows all possible domain names to be of course following the encoding rules of 5 however certain encoded provided the encoding rules are observed per 5 however applications may restrict the set of valid characters Care should certain applications may restrict the set of valid characters Care be taken so that invalid characters in these contexts does not cause should be taken so that invalid characters in these contexts does not harm In particular host names in the DNS have certain cause harm In particular host names in the DNS have certain restrictions It is up to these application to limit this subset restrictions It is up to these application to limit this subset this URI scheme places no restrictions this URI scheme places no restrictions Intended usage Whenever DNS resources are useful to reference by Intended usage Whenever it is useful for DNS resources to be protocol independent identifiers often when the data is more referenced by protocol independent identifiers this URI important than the access method Since software in general has specification is applicable Often this occurs when the data is more important than the access method Since software in general has coped without this so far it is not anticipated to be implemented coped without this so far it is not anticipated to be implemented widely nor migrated to by existing systems but specific solutions widely nor migrated to by existing systems but specific solutions especially security related may find this appropriate especially security related may find this appropriate Applications and or protocols which use this scheme Security related Applications and or protocols which use this scheme Security software DNS administration tools Network programming packages related software DNS administration tools and network programming packages Interoperability considerations The data referenced by this URI Interoperability considerations The data referenced by this URI scheme might be transferred by protocols that are not URI aware such scheme might be transferred by protocols that are not URI aware such as the DNS protocol This is not anticipated to have any serious as the DNS protocol This is not anticipated to have any serious interoperability impact though interoperability impact Interoperability problems may occur if one entity understands a new Interoperability problems may occur if one entity understands a new DNS class type mnemonic and another entity do not understand it DNS class type mnemonic that another entity does not This is an This is an interoperability problem for DNS software in general interoperability problem for DNS software in general although it is although it is not a major practical problem as the DNS types and not a major practical problem for current DNS deployments as the DNS classes are fairly static To guarantee interoperability types and classes are fairly static To guarantee interoperability implementations can use integers for all mnemonics not defined in implementations can use integers for all mnemonics not defined in 2 2 Interaction with Binary Labels 12 or other extended label types Interaction with Binary Labels 10 or other extended label types has has not been analyzed However they appear to be infrequently used not been analyzed However they appear to be infrequently used in in practice practice Contact simon josefsson org Contact simon josefsson org Author Change Controller simon josefsson org Author Change Controller simon josefsson org 4 Examples 4 Examples A DNS URI is of the following general form This is intended to A DNS URI is of the following general form This is intended to illustrate not define the scheme illustrate not define the scheme dns authority domain CLASS class TYPE type dns authority domain CLASS class TYPE type The following illustrate a URI for a resource with the absolute name The following illustrate s a URI for a resource with the absolute name www example org the Internet IN class and the Address A type www example org the Internet IN class and the Address A type dns www example org clAsS IN tYpE A dns www example org clAsS IN tYpE A Since the default class is IN and the default type is A the same Since the default class is IN and the default type is A the same resource can be identified by a shorter URI using a relative name resource can be identified by a shorter URI using a relative name dns www example org dns www example org The following illustrate a URI for a resource with the name The following illustrate a URI for a resource with the name simon example org for the CERT type in the Internet IN class simon example org for the CERT type in the Internet IN class dns simon example org type CERT dns simon example org type CERT The following illustrate a URI for a resource with the name The following illustrate a URI for a resource with the name ftp example org in the Internet IN class and the address A ftp example org in the Internet IN class and the address A type but from the DNS authority 192 168 1 1 instead of the default type but from the DNS authority 192 168 1 1 instead of the default authority authority dns 192 168 1 1 ftp example org type A dns 192 168 1 1 ftp example org type A The following illustrate various escaping techniques The owner name The following illustrates various escaping techniques The owner would be world wide web example domain org where denote the name would be world wide web example domain example where character as part of a label and denote the label separator denotes the character as part of a label and denotes the label separator dns world 20wide 20web example 5c domain example TYPE TXT dns world 20wide 20web example 5c domain example TYPE TXT The following illustrate a strange but valid DNS resource The following illustrate s a strange but valid DNS resource dns fw example org 20 00 example type TXT dns fw example org 20 00 example type TXT 5 Acknowledgments 5 Acknowledgments Thanks to Stuart Cheshire Donald Eastlake Pasi Eronen Bill Fenner Thanks to Stuart Cheshire Donald Eastlake Pasi Eronen Bill Fenner Ted Hardie Russ Housley Peter Koch Andrew Main Larry Masinter Ted Hardie Russ Housley Peter Koch Andrew Main Larry Masinter Michael Mealling Steve Mattson Paul Vixie Sam Weiler and Bert Michael Mealling Steve Mattson Marcos Sanz Jason Sloderbeck Paul Wijnen for comments and suggestions The author acknowledges the RSA Vixie Sam Weiler and Bert Wijnen for comments and suggestions The Laboratories for supporting the work that led to this document author acknowledges RSA Laboratories for supporting the work that led to this document 6 Security Considerations 6 Security Considerations If a DNS URI references domains in the Internet DNS environment both If a DNS URI references domains in the Internet DNS environment both the URI itself and the information referenced by the URI is public the URI itself and the information referenced by the URI is public information If a DNS URI is used within an internal DNS information If a DNS URI is used within an internal DNS environment both the DNS URI and the data is referenced should be environment both the DNS URI and the data is referenced should be handled using the same considerations that apply to DNS data in the handled using the same considerations that apply to DNS data in the environment internal environment If information referenced by DNS URIs are used to make security If information referenced by DNS URIs are used to make security decisions examples of such data include but is not limited to decisions examples of such data include but is not limited to certificates stored in the DNS 10 implementations may need to certificates stored in the DNS 9 implementations may need to employ security techniques such as Secure DNS 9 or even CMS 15 employ security techniques such as Secure DNS 16 CMS 13 or or OpenPGP 8 to protect the data during transport How to OpenPGP 8 to protect the data during transport How to implement implement this will depend on the usage scenario and it is not up to this will depend on the usage scenario and it is not up to this URI this URI scheme to define how the data referenced by DNS URIs should scheme to define how the data referenced by DNS URIs should be be protected protected If applications accept unknown dnsqueryelement values e g accepts If applications accept unknown dnsqueryelement values in a URI e g the URI dns www example org secret value without knowing what the URI dns www example org secret value without knowing what the secret value dnsqueryelement means a covert channel used to secret value dnsqueryelement means a covert channel used to leak leak information may be enabled The implications of covert information may be enabled The implications of covert channels channels should be understood by applications that accepts unknown should be understood by applications that accept unknown dnsqueryelement values dnsqueryelement values Slight variations such as difference between upper and lower case in Slight variations such as difference between upper and lower case in the dnsname field can be used as a covert channel to leak the dnsname field can be used as a covert channel to leak information information 7 IANA Considerations 7 IANA Considerations The IANA is asked to register the DNS URI scheme using the template The IANA is asked to register the DNS URI scheme using the template in section 3 in accordance with RFC 2717 1 3 in section 3 in accordance with RFC 2717 1 1 8 Copying conditions 8 Copying conditions Copyright c 2000 2001 2002 2003 2004 2005 Simon Josefsson Copyright c 2000 2001 2002 2003 2004 2005 Simon Josefsson Regarding this entire document or any portion of it the author makes Regarding this entire document or any portion of it the author makes no guarantees and is not responsible for any damage resulting from no guarantees and is not responsible for any damage resulting from its use The author grants irrevocable permission to anyone to use its use The author grants irrevocable permission to anyone to use modify and distribute it in any way that does not diminish

    Original URL path: http://www.josefsson.org/dns-url/draft-josefsson-dns-url-from--13.diff.html (2016-04-30)
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  • Diff: draft-josefsson-dns-url.txt - rfc4501.txt
    Normative References 9 1 Normative References 1 Mockapetris P Domain names concepts and facilities 1 Mockapetris P Domain names concepts and facilities STD STD 13 RFC 1034 November 1987 13 RFC 1034 November 1987 2 Mockapetris P Domain names implementation and 2 Mockapetris P Domain names implementation and specification STD 13 RFC 1035 November 1987 specification STD 13 RFC 1035 November 1987 3 Bradner S Key words for use in RFCs to Indicate Requirement 3 Bradner S Key words for use in RFCs to Indicate Requirement Levels BCP 14 RFC 2119 March 1997 Levels BCP 14 RFC 2119 March 1997 4 Crocker D and P Overell Augmented BNF for Syntax 4 Crocker D and P Overell Augmented BNF for Syntax Specifications ABNF RFC 4234 October 2005 Specifications ABNF RFC 4234 October 2005 5 Berners Lee T Fielding R and L Masinter Uniform 5 Berners Lee T Fielding R and L Masinter Uniform Resource Identifier URI Generic Syntax STD 66 RFC 3986 Resource Identifier URI Generic Syntax STD 66 RFC 3986 January 2005 January 2005 9 2 Informative References 9 2 Informative References 6 Postel J and J Reynolds File Transfer Protocol STD 9 6 Postel J and J Reynolds File Transfer Protocol STD 9 RFC RFC 959 October 1985 959 October 1985 7 Freed N Klensin J and J Postel Multipurpose Internet 7 Freed N Klensin J and J Postel Multipurpose Internet Mail Extensions MIME Part Four Registration Procedures Mail Extensions MIME Part Four Registration Procedures BCP BCP 13 RFC 2048 November 1996 13 RFC 2048 November 1996 8 Callas J Donnerhacke L Finney H and R Thayer 8 Callas J Donnerhacke L Finney H and R Thayer OpenPGP OpenPGP Message Format RFC 2440 November 1998 Message Format RFC 2440 November 1998 9 Eastlake D and O Gudmundsson Storing Certificates in the 9 Eastlake 3rd D and O Gudmundsson Storing Certificates in Domain Name System DNS RFC 2538 March 1999 the Domain Name System DNS RFC 2538 March 1999 10 Crawford M Binary Labels in the Domain Name System 10 Crawford M Binary Labels in the Domain Name System RFC RFC 2673 August 1999 2673 August 1999 11 Petke R and I King Registration Procedures for URL Scheme 11 Petke R and I King Registration Procedures for URL Scheme Names BCP 35 RFC 2717 November 1999 Names BCP 35 RFC 2717 November 1999 12 Connolly D and L Masinter The text html Media Type 12 Connolly D and L Masinter The text html Media Type RFC RFC 2854 June 2000 2854 June 2000 13 Housley R Cryptographic Message Syntax CMS RFC 3852 13 Housley R Cryptographic Message Syntax CMS RFC 3852 July 2004 July 2004 14 Faltstrom P Hoffman P and A Costello 14 Faltstrom P Hoffman P and A Costello Internationalizing Internationalizing Domain Names in Applications IDNA Domain Names in Applications IDNA RFC 3490 March 2003 RFC 3490 March 2003 15 Josefsson S Domain Name System Media Types RFC 4027 15 Josefsson S Domain Name System Media Types RFC

    Original URL path: http://www.josefsson.org/dns-url/rfc4501-from-draft-josefsson-dns-url.diff.html (2016-04-30)
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  • Diff: draft-josefsson-dns-url-12.txt - draft-josefsson-dns-url.txt
    detailed URI syntax that map more certain applications a more detailed URI syntax that map more closely to the DNS protocol may be required However such an URI closely to the DNS protocol may be required However such an URI definition is not included in this document This document specify a definition is not included in this document This document specify a URI that is primarily intended to name DNS resources but it can also URI that is primarily intended to name DNS resources but it can also be used to locate said resources for simple but common be used to locate said resources for simple but common applications applications 3 DNS URI Registration 3 DNS URI Registration The section contain the registration template for the DNS URI scheme The section contain the registration template for the DNS URI scheme in accordance with 1 2 in accordance with 1 3 URL scheme name dns URL scheme name dns URL scheme syntax A DNS URI designate a DNS resource record set URL scheme syntax A DNS URI designate a DNS resource record set referenced by domain name class type and optionally the authority referenced by domain name class type and optionally the authority The DNS URI follows the generic syntax from RFC 3986 5 and is The DNS URI follows the generic syntax from RFC 3986 5 and is described using ABNF 4 Strings are not case sensitive and free described using ABNF 4 Strings are not case sensitive and free insertion of linear white space is not permitted insertion of linear white space is not permitted dnsurl dns dnsauthority dnsurl dns dnsauthority skipping to change at page 7 line 46 skipping to change at page 7 line 46 interoperability impact though interoperability impact though Interoperability problems may occur if one entity understands a new Interoperability problems may occur if one entity understands a new DNS class type mnemonic and another entity do not understand it DNS class type mnemonic and another entity do not understand it This is an interoperability problem for DNS software in general This is an interoperability problem for DNS software in general although it is not a major practical problem as the DNS types and although it is not a major practical problem as the DNS types and classes are fairly static To guarantee interoperability classes are fairly static To guarantee interoperability implementations can use integers for all mnemonics not defined in implementations can use integers for all mnemonics not defined in 2 2 Interaction with Binary Labels 1 1 or other extended label types Interaction with Binary Labels 1 2 or other extended label types has not been analyzed However they appear to be infrequently used has not been analyzed However they appear to be infrequently used in practice in practice Contact simon josefsson org Contact simon josefsson org Author Change Controller simon josefsson org Author Change Controller simon josefsson org 4 Examples 4 Examples A DNS URI is of the following general form This is intended to A DNS URI is of the following general form This is intended to illustrate not define the scheme illustrate not define the scheme skipping to change at page 9 line 24 skipping to change at page 9 line 24 If a DNS URI references domains in the Internet DNS environment both If a DNS URI references domains in the Internet DNS environment both the URI itself and the information referenced by the URI is public the URI itself and the information referenced by the URI is public information If a DNS URI is used within an internal DNS information If a DNS URI is used within an internal DNS environment both the DNS URI and the data is referenced should be environment both the DNS URI and the data is referenced should be handled using the same considerations that apply to DNS data in the handled using the same considerations that apply to DNS data in the environment environment If information referenced by DNS URIs are used to make security If information referenced by DNS URIs are used to make security decisions examples of such data include but is not limited to decisions examples of such data include but is not limited to certificates stored in the DNS implementations may need to employ certificates stored in the DNS 10 implementations may need to security techniques such as Secure DNS 8 or even CMS 15 or employ security techniques such as Secure DNS 9 or even CMS 15 OpenPGP 7 to protect the data during transport How to implement or OpenPGP 8 to protect the data during transport How to this will depend on the usage scenario and it is not up to this URI implement this will depend on the usage scenario and it is not up to scheme to define how the data referenced by DNS URIs should be this URI scheme to define how the data referenced by DNS URIs should protected be protected If applications accept unknown dnsqueryelement values e g accepts If applications accept unknown dnsqueryelement values e g accepts the URI dns www example org secret value without knowing what the the URI dns www example org secret value without knowing what the secret value dnsqueryelement means a covert channel used to secret value dnsqueryelement means a covert channel used to leak information may be enabled The implications of covert leak information may be enabled The implications of covert channels should be understood by applications that accepts unknown channels should be understood by applications that accepts unknown dnsqueryelement values dnsqueryelement values Slight variations such as difference between upper and lower case in Slight variations such as difference between upper and lower case in the dnsname field can be used as a covert channel to leak the dnsname field can be used as a covert channel to leak information information 7 IANA Considerations 7 IANA Considerations The IANA is asked to register the DNS URI scheme using the template The IANA is asked

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  • given in the URI string this indicate the server that should receive the DNS query otherwise the default DNS server should receive it Note that DNS URIs could be resolved by other protocols than the DNS protocol or by using the DNS protocol in some other way than as described above e g multicast DNS DNS URIs do not require the use of the DNS protocol although it is expected to be the typical usage The previous paragraph only illustrate how DNS URIs are resolved using the DNS protocol A client MAY want to check that it understands the dnsclassval and dnstypeval before sending a query so that it will be able to understand the response However a typical example of a client that would not need to check dnsclassval and dnstypeval would be a proxy that would just treat the received answer as opaque data Character encoding considerations The characters are encoded as per RFC 3986 5 The DNS protocol do not consider character sets it simply transports opaque data In particular the dnsname field of the DNS URI is to be considered an internationalized domain name IDN unaware domain name slot in the terminology of 16 The considerations for host and port are discussed in 5 Josefsson Expires November 26 2005 Page 6 Internet Draft DNS URI May 2005 Because is used as the DNS label separator an escaping mechanism is required to encode a that is part of a DNS label The escaping mechanism is described in section 5 1 of RFC 1035 For example a DNS label of exa mple can be escaped as exa mple or exa 046mple However the URI specification disallow the character from occuring directly in URIs so it must be escaped as 5c The single DNS label exa mple is thus encoded as exa 5c mple The same mechanism can be used to encode other characters for example and Note that and 2e are equivalent within dnsname and are interchangable This URI specification allows all possible domain names to be encoded of course following the encoding rules of 5 however certain applications may restrict the set of valid characters Care should be taken so that invalid characters in these contexts does not cause harm In particular host names in the DNS have certain restrictions It is up to these application to limit this subset this URI scheme places no restrictions Intended usage Whenever DNS resources are useful to reference by protocol independent identifiers often when the data is more important than the access method Since software in general has coped without this so far it is not anticipated to be implemented widely nor migrated to by existing systems but specific solutions especially security related may find this appropriate Applications and or protocols which use this scheme Security related software DNS administration tools Network programming packages Interoperability considerations The data referenced by this URI scheme might be transferred by protocols that are not URI aware such as the DNS protocol This is not anticipated to have any serious interoperability impact though Interoperability problems may occur if one entity understands a new DNS class type mnemonic and another entity do not understand it This is an interoperability problem for DNS software in general although it is not a major practical problem as the DNS types and classes are fairly static To guarantee interoperability implementations can use integers for all mnemonics not defined in 2 Interaction with Binary Labels 11 or other extended label types has not been analyzed However they appear to be infrequently used in practice Contact simon josefsson org Josefsson Expires November 26 2005 Page 7 Internet Draft DNS URI May 2005 Author Change Controller simon josefsson org 4 Examples A DNS URI is of the following general form This is intended to illustrate not define the scheme dns authority domain CLASS class TYPE type The following illustrate a URI for a resource with the absolute name www example org the Internet IN class and the Address A type dns www example org clAsS IN tYpE A Since the default class is IN and the default type is A the same resource can be identified by a shorter URI using a relative name dns www example org The following illustrate a URI for a resource with the name simon example org for the CERT type in the Internet IN class dns simon example org type CERT The following illustrate a URI for a resource with the name ftp example org in the Internet IN class and the address A type but from the DNS authority 192 168 1 1 instead of the default authority dns 192 168 1 1 ftp example org type A The following illustrate various escaping techniques The owner name would be world wide web example domain org where denote the character as part of a label and denote the label separator dns world 20wide 20web example 5c domain example TYPE TXT The following illustrate a strange but valid DNS resource dns fw example org 20 00 example type TXT Josefsson Expires November 26 2005 Page 8 Internet Draft DNS URI May 2005 5 Acknowledgments Thanks to Stuart Cheshire Donald Eastlake Pasi Eronen Bill Fenner Ted Hardie Russ Housley Peter Koch Andrew Main Larry Masinter Michael Mealling Steve Mattson Paul Vixie Sam Weiler and Bert Wijnen for comments and suggestions The author acknowledges the RSA Laboratories for supporting the work that led to this document 6 Security Considerations If a DNS URI references domains in the Internet DNS environment both the URI itself and the information referenced by the URI is public information If a DNS URI is used within an internal DNS environment both the DNS URI and the data is referenced should be handled using the same considerations that apply to DNS data in the environment If information referenced by DNS URIs are used to make security decisions examples of such data include but is not limited to certificates stored in the DNS implementations may need

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  • Diff: draft-josefsson-dns-url-11.txt - draft-josefsson-dns-url-12.txt
    queries and render Data browsers may support DNS URIs by forming DNS queries and render DNS responses using HTML 13 similar to what is commonly done for DNS responses using HTML 13 similar to what is commonly done for FTP 5 resources FTP 6 resources The key words MUST MUST NOT REQUIRED SHALL SHALL NOT The key words MUST MUST NOT REQUIRED SHALL SHALL NOT SHOULD SHOULD NOT RECOMMENDED MAY and OPTIONAL in this SHOULD SHOULD NOT RECOMMENDED MAY and OPTIONAL in this document are to be interpreted as described in RFC 2119 6 document are to be interpreted as described in RFC 2119 3 2 Usage Model 2 Usage Model The reader is referred to section 1 of 4 for an in depth discussion The reader is referred to section 1 of 5 for an in depth discussion of URI classifications In particular the reader is assumed to be of URI classifications In particular the reader is assumed to be familiar with the name vs locator distinction This section familiar with the name vs locator distinction This section describe how the DNS URI scheme is intended to be used and outline describe how the DNS URI scheme is intended to be used and outline future work that may be required to use URIs with the DNS for some future work that may be required to use URIs with the DNS for some applications applications The URI scheme described in this document focus on the data stored in The URI scheme described in this document focus on the data stored in the DNS As such there is no provision to specify any of the fields the DNS As such there is no provision to specify any of the fields in the actual DNS protocol This is intentional so that the URI may in the actual DNS protocol This is intentional so that the URI may be used even in situations where the DNS protocol is not used be used even in situations where the DNS protocol is not used skipping to change at page 5 line 14 skipping to change at page 5 line 14 3 DNS URI Registration 3 DNS URI Registration The section contain the registration template for the DNS URI scheme The section contain the registration template for the DNS URI scheme in accordance with 12 in accordance with 12 URL scheme name dns URL scheme name dns URL scheme syntax A DNS URI designate a DNS resource record set URL scheme syntax A DNS URI designate a DNS resource record set referenced by domain name class type and optionally the authority referenced by domain name class type and optionally the authority The DNS URI follows the generic syntax from RFC 3986 4 and is The DNS URI follows the generic syntax from RFC 3986 5 and is described using ABNF 3 Strings are not case sensitive and free described using ABNF 4 Strings are not case sensitive and free insertion of linear white space is not permitted insertion of linear white space is not permitted dnsurl dns dnsauthority dnsurl dns dnsauthority dnsname dnsquery dnsname dnsquery dnsauthority host port dnsauthority host port See RFC 3986 for the See RFC 3986 for the definition of host and port definition of host and port dnsname pchar dnsname pchar skipping to change at page 5 line 44 skipping to change at page 5 line 44 dnsname value is to be dnsname value is to be interpreted as the root itself interpreted as the root itself See below on relative dnsname s See below on relative dnsname s dnsquery dnsqueryelement dnsquery dnsquery dnsqueryelement dnsquery dnsqueryelement CLASS dnsclassval TYPE dnstypeval dnsqueryelement CLASS dnsclassval TYPE dnstypeval Each clause MUST NOT be used more Each clause MUST NOT be used more than once than once dnsclassval 1 digit IN CH dnsclassval 1 digit IN CH Any IANA registered DNS class Any IANA registered DNS class mnemonic expressed as mnemonic or as decimal integer dnstypeval 1 digit A NS MD dnstypeval 1 digit A NS MD Any IANA registered DNS type Any IANA registered DNS type mnemonic expressed as mnemonic or as decimal integer Unless specified in the URI the authority dnsauthority is Unless specified in the URI the authority dnsauthority is assumed to be locally known the class dnsclassval to be the assumed to be locally known the class dnsclassval to be the Internet class IN and the type dnstypeval to be the Address Internet class IN and the type dnstypeval to be the Address type A These default values match the typical use of DNS to type A These default values match the typical use of DNS to look up addresses for host names look up addresses for host names A dnsquery element MUST NOT contain more than one occurance of the A dnsquery element MUST NOT contain more than one occurance of the CLASS and TYPE fields For example both CLASS and TYPE fields For example both dns dns example TYPE A TYPE TXT and dns example TYPE A TYPE A are example TYPE A TYPE TXT and dns example TYPE A TYPE A are invalid invalid However the fields may occur in any order so that both However the fields may occur in any order so that both dns dns example TYPE A CLASS IN and dns example CLASS IN TYPE A are example TYPE A CLASS IN and dns example CLASS IN TYPE A are valid valid The digit representation of types and classes MAY be used when a The digit representation of types and classes MAY be used when a mnemonic for the corresponding value is not well known e g for mnemonic for the corresponding value is not well known e g for newly introduced types or classes but SHOULD NOT be used for the newly introduced types or classes but SHOULD NOT be used for the types or classes defined in the DNS specification 2 All types or classes defined in the DNS specification 2 All implementations MUST recognize the mnemonics defined in 2 implementations MUST recognize the mnemonics defined in 2 To avoid ambiguity relative dnsname values i e those not ending To avoid ambiguity relative dnsname values i e those not ending with are assumed to be relative to the root For example with are assumed to be relative to the root For example dns dns host example and dns host example both refer to the same host example and dns host example both refer to the same owner owner name namely host example Further an empty dnsname name namely host example Further an empty dnsname value is value is considered to be a degenerative form of a relative name considered to be a degenerative form of a relative name which refer which refer to the root to the root To resolve a DNS URI using the DNS protocol 2 a query is created To resolve a DNS URI using the DNS protocol 2 a query is created using as input the dnsname dnsclassval and dnstypeval from the URI using as input the dnsname dnsclassval and dnstypeval from the URI string or the appropriate default values If an authority string or the appropriate default values If an authority dnsauthority is given in the URI string this indicate the server dnsauthority is given in the URI string this indicate the server that should receive the DNS query otherwise the default DNS server that should receive the DNS query otherwise the default DNS server should receive it should receive it Note that DNS URIs could be resolved by other protocols than the DNS Note that DNS URIs could be resolved by other protocols than the DNS protocol or by using the DNS protocol in some other way than as protocol or by using the DNS protocol in some other way than as skipping to change at page 6 line 52 skipping to change at page 6 line 47 usage The previous paragraph only illustrate how DNS URIs are usage The previous paragraph only illustrate how DNS URIs are resolved using the DNS protocol resolved using the DNS protocol A client MAY want to check that it understands the dnsclassval and A client MAY want to check that it understands the dnsclassval and dnstypeval before sending a query so that it will be able to dnstypeval before sending a query so that it will be able to understand the response However a typical example of a client that understand the response However a typical example of a client that would not need to check dnsclassval and dnstypeval would be a proxy would not need to check dnsclassval and dnstypeval would be a proxy that would just treat the received answer as opaque data that would just treat the received answer as opaque data Character encoding considerations The characters are encoded as per Character encoding considerations The characters are encoded as per RFC 3986 4 The DNS protocol do not consider character sets it RFC 3986 5 The DNS protocol do not consider character sets it simply transports opaque data In particular the dnsname field of simply transports opaque data In particular the dnsname field of the DNS URI is to be considered an internationalized domain name the DNS URI is to be considered an internationalized domain name IDN unaware domain name slot in the terminology of 15 The IDN unaware domain name slot in the terminology of 16 The considerations for host and port are discussed in 4 considerations for host and port are discussed in 5 Because is used as the DNS label separator an escaping mechanism Because is used as the DNS label separator an escaping mechanism is required to encode a that is part of a DNS label The is required to encode a that is part of a DNS label The escaping mechanism is described in section 5 1 of RFC 1035 For escaping mechanism is described in section 5 1 of RFC 1035 For example a DNS label of exa mple can be escaped as exa mple or example a DNS label of exa mple can be escaped as exa mple or exa 046mple However the URI specification disallow the exa 046mple However the URI specification disallow the character from occuring directly in URIs so it must be escaped as character from occuring directly in URIs so it must be escaped as 5c The single DNS label exa mple is thus encoded as 5c The single DNS label exa mple is thus encoded as exa exa 5c mple The same mechanism can be used to encode other 5c mple The same mechanism can be used to encode other characters characters for example and Note that and 2e are for example and Note that and 2e are equivalent equivalent within dnsname and are interchangable within dnsname and are interchangable This URI specification allows all possible domain names to be encoded This URI specification allows all possible domain names to be encoded of course following the encoding rules of 4 however certain of course following the encoding rules of 5 however certain applications may restrict the set of valid characters Care should applications may restrict the set of valid characters Care should be taken so that invalid characters in these contexts does not cause be taken so that invalid characters in these contexts does not cause harm In particular host names in the DNS have certain harm In particular host names in the DNS have certain restrictions It is up to these application to limit this subset restrictions It is up to these application to limit this subset this URI scheme places no restrictions this URI scheme places no restrictions Intended usage Whenever DNS resources are useful to reference by Intended usage Whenever DNS resources are useful to reference by protocol independent identifiers often when the data is more protocol independent identifiers often when the data is more important than the access method Since software in general has important than the access method Since software in general has coped without this so far it is not anticipated to be implemented coped without this so far it is not anticipated to be implemented skipping to change at page 8 line 42 skipping to change at page 8 line 37 The following illustrate a URI for a resource with the name The following illustrate a URI for a resource with the name ftp example org in the Internet IN class and the address A ftp example org in the Internet IN class and the address A type but from the DNS authority 192 168 1 1 instead of the default type but from the DNS authority 192 168 1 1 instead of the default authority authority dns 192 168 1 1 ftp example org type A dns 192 168 1 1 ftp example org type A The following illustrate various escaping techniques The owner name The following illustrate various escaping techniques The owner name would be world wide web example domain org where denote the would be world wide web example domain org where denote the character as part of a label and denote the label character as part of a label and denote the label separator separator dns world 20wide 20web example 5c domain example TYPE TXT dns world 20wide 20web example 5c domain example TYPE TXT The following illustrate a strange but valid DNS resource The following illustrate a strange but valid DNS resource dns fw example org 20 00 example type TXT dns fw example org 20 00 example type TXT 5 Acknowledgments 5 Acknowledgments Thanks to Stuart Cheshire Donald Eastlake Pasi Eronen Ted Hardie Thanks to Stuart Cheshire Donald Eastlake Pasi Eronen Bill Fenner Peter Koch Andrew Main Larry Masinter Michael Mealling Steve Ted Hardie Russ Housley Peter Koch Andrew Main Larry Masinter Mattson and Paul Vixie for comments and suggestions The author Michael Mealling Steve Mattson Paul Vixie Sam Weiler and Bert acknowledges the RSA Laboratories for supporting the work that led to Wijnen for comments and suggestions The author acknowledges the RSA this document Laboratories for supporting the work that led to this document 6 Security Considerations 6 Security Considerations If a DNS URI references domains in the Internet DNS environment both If a DNS URI references domains in the Internet DNS environment both the URI itself and the information referenced by the URI is public the URI itself and the information referenced by the URI is public information If a DNS URI is used within an internal DNS information If a DNS URI is used within an internal DNS environment both the DNS URI and the data is referenced should be environment both the DNS URI and the data is referenced should be handled using the same considerations that apply to DNS data in the handled using the same considerations that apply to DNS data in the environment environment If information referenced by DNS URIs are used to make security If information referenced by DNS URIs are used to make security decisions examples of such data include but is not limited to decisions examples of such data include but is not limited to certificates stored in the DNS implementations may need to employ certificates stored in the DNS implementations may need to employ security techniques such as Secure DNS 8 or even CMS 1 4 or security techniques such as Secure DNS 8 or even CMS 1 5 or OpenPGP 7 to protect the data during transport How to implement OpenPGP 7 to protect the data during transport How to implement this will depend on the usage scenario and it is not up to this URI this will depend on the usage scenario and it is not up to this URI scheme to define how the data referenced by DNS URIs should be scheme to define how the data referenced by DNS URIs should be protected protected If applications accept unknown dnsqueryelement values e g accepts If applications accept unknown dnsqueryelement values e g accepts the URI dns www example org secret value without knowing what the the URI dns www example org secret value without knowing what the secret value dnsqueryelement means a covert channel used to secret value dnsqueryelement means a covert channel used to leak information may be enabled The implications of covert leak information may be enabled The implications of covert channels should be understood by applications that accepts unknown channels should be understood by applications that accepts unknown dnsqueryelement values dnsqueryelement values Slight variations such as difference between upper and lower case in Slight variations such as difference between upper and lower case in the dnsname field can be used as a covert channel to leak the dnsname field can be used as a covert channel to leak information information 7 IANA Considerations 7 IANA Considerations The IANA is asked to register the DNS URI scheme using the template The IANA is asked to register the DNS URI scheme using the template in section 2 in accordance with RFC 2717 12 in section 3 in accordance with RFC 2717 12 8 Copying conditions 8 Copying conditions Copyright c 2000 2001 2002 2003 2004 2005 Simon Josefsson Regarding this entire document or any portion of it the author makes Regarding this entire document or any portion of it the author makes no guarantees and is not responsible for any damage resulting from no guarantees and is not responsible for any damage resulting from its use The author grants irrevocable permission to anyone to use its use The author grants irrevocable permission to anyone to use modify and distribute it in any way that does not diminish the modify and distribute it in any way that does not diminish the rights of anyone else to use modify and distribute it provided rights of anyone else to use modify and distribute it provided that redistributed derivative works do not contain misleading author that redistributed derivative works do not contain misleading author or version information Derivative works need not

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  • is considered to be a degenerative form of a relative name which refer to the root To resolve a DNS URI using the DNS protocol 2 a query is created using as input the dnsname dnsclassval and dnstypeval from the URI string or the appropriate default values If an authority dnsauthority is given in the URI string this indicate the server that should receive the DNS query otherwise the default DNS server should receive it Note that DNS URIs could be resolved by other protocols than the DNS protocol or by using the DNS protocol in some other way than as described above e g multicast DNS DNS URIs do not require the use of the DNS protocol although it is expected to be the typical usage The previous paragraph only illustrate how DNS URIs are resolved using the DNS protocol A client MAY want to check that it understands the dnsclassval and dnstypeval before sending a query so that it will be able to understand the response However a typical example of a client that would not need to check dnsclassval and dnstypeval would be a proxy that would just treat the received answer as opaque data Character encoding considerations The characters are encoded as per RFC 3986 4 The DNS protocol do not consider character sets it Josefsson Expires August 11 2005 Page 6 Internet Draft DNS URI February 2005 simply transports opaque data In particular the dnsname field of the DNS URI is to be considered an internationalized domain name IDN unaware domain name slot in the terminology of 15 The considerations for host and port are discussed in 4 Because is used as the DNS label separator an escaping mechanism is required to encode a that is part of a DNS label The escaping mechanism is described in section 5 1 of RFC 1035 For example a DNS label of exa mple can be escaped as exa mple or exa 046mple However the URI specification disallow the character from occuring directly in URIs so it must be escaped as 5c The single DNS label exa mple is thus encoded as exa 5c mple The same mechanism can be used to encode other characters for example and Note that and 2e are equivalent within dnsname and are interchangable This URI specification allows all possible domain names to be encoded of course following the encoding rules of 4 however certain applications may restrict the set of valid characters Care should be taken so that invalid characters in these contexts does not cause harm In particular host names in the DNS have certain restrictions It is up to these application to limit this subset this URI scheme places no restrictions Intended usage Whenever DNS resources are useful to reference by protocol independent identifiers often when the data is more important than the access method Since software in general has coped without this so far it is not anticipated to be implemented widely nor migrated to by existing systems but specific solutions especially security related may find this appropriate Applications and or protocols which use this scheme Security related software DNS administration tools Network programming packages Interoperability considerations The data referenced by this URI scheme might be transferred by protocols that are not URI aware such as the DNS protocol This is not anticipated to have any serious interoperability impact though Interoperability problems may occur if one entity understands a new DNS class type mnemonic and another entity do not understand it This is an interoperability problem for DNS software in general although it is not a major practical problem as the DNS types and classes are fairly static To guarantee interoperability implementations can use integers for all mnemonics not defined in 2 Interaction with Binary Labels 11 or other extended label types Josefsson Expires August 11 2005 Page 7 Internet Draft DNS URI February 2005 has not been analyzed However they appear to be infrequently used in practice Contact simon josefsson org Author Change Controller simon josefsson org 4 Examples A DNS URI is of the following general form This is intended to illustrate not define the scheme dns authority domain CLASS class TYPE type The following illustrate a URI for a resource with the absolute name www example org the Internet IN class and the Address A type dns www example org clAsS IN tYpE A Since the default class is IN and the default type is A the same resource can be identified by a shorter URI using a relative name dns www example org The following illustrate a URI for a resource with the name simon example org for the CERT type in the Internet IN class dns simon example org type CERT The following illustrate a URI for a resource with the name ftp example org in the Internet IN class and the address A type but from the DNS authority 192 168 1 1 instead of the default authority dns 192 168 1 1 ftp example org type A The following illustrate various escaping techniques The owner name would be world wide web example domain org where denote the character as part of a label and denote the label separator dns world 20wide 20web example 5c domain example TYPE TXT The following illustrate a strange but valid DNS resource dns fw example org 20 00 example type TXT Josefsson Expires August 11 2005 Page 8 Internet Draft DNS URI February 2005 5 Acknowledgments Thanks to Stuart Cheshire Donald Eastlake Pasi Eronen Ted Hardie Peter Koch Andrew Main Larry Masinter Michael Mealling Steve Mattson and Paul Vixie for comments and suggestions The author acknowledges the RSA Laboratories for supporting the work that led to this document 6 Security Considerations If a DNS URI references domains in the Internet DNS environment both the URI itself and the information referenced by the URI is public information If a DNS URI is used within an internal DNS environment both the DNS URI and the data is referenced should

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  • Diff: draft-josefsson-dns-url-10.txt - draft-josefsson-dns-url-11.txt
    occurance of the CLASS and TYPE fields For example both CLASS and TYPE fields For example both dns example TYPE A TYPE TXT and dns example TYPE A TYPE A are dns example TYPE A TYPE TXT and dns example TYPE A TYPE A are skipping to change at page 5 line 44 skipping to change at page 6 line 52 usage The previous paragraph only illustrate how DNS URIs are usage The previous paragraph only illustrate how DNS URIs are resolved using the DNS protocol resolved using the DNS protocol A client MAY want to check that it understands the dnsclassval and A client MAY want to check that it understands the dnsclassval and dnstypeval before sending a query so that it will be able to dnstypeval before sending a query so that it will be able to understand the response However a typical example of a client that understand the response However a typical example of a client that would not need to check dnsclassval and dnstypeval would be a proxy would not need to check dnsclassval and dnstypeval would be a proxy that would just treat the received answer as opaque data that would just treat the received answer as opaque data Character encoding considerations The characters are encoded as per Character encoding considerations The characters are encoded as per the URI Generic Syntax RFC 4 The DNS protocol do not consider RFC 3986 4 The DNS protocol do not consider character sets it character sets it simply transports opaque data In particular the simply transports opaque data In particular the dnsname field of dnsname field of the DNS URI is to be considered an the DNS URI is to be considered an internationalized domain name internationalized domain name IDN unaware domain name slot in the IDN unaware domain name slot in the terminology of 15 The terminology of 15 The considerations for hostport are discussed considerations for host and port are discussed in 4 in 4 Because is used as the DNS label separator an escaping mechanism Because is used as the DNS label separator an escaping mechanism is required to encode a that is part of a DNS label The is required to encode a that is part of a DNS label The escaping mechanism is described in section 5 1 of RFC 1035 For escaping mechanism is described in section 5 1 of RFC 1035 For example a DNS label of exa mple can be escaped as exa mple or example a DNS label of exa mple can be escaped as exa mple or exa 046mple However the URI specification disallow the exa 046mple However the URI specification disallow the character from occuring directly in URIs so it must be escaped as character from occuring directly in URIs so it must be escaped as 5c The single DNS label exa mple is thus encoded as 5c The single DNS label exa mple is thus encoded as exa 5c mple The same mechanism can be used to encode other exa 5c mple The same mechanism can be used to encode other characters for example and Note that and 2e are characters for example and Note that and 2e are equivalent within dnsname and are interchangable equivalent within dnsname and are interchangable This URI specification allows all possible domain names to be encoded This URI specification allows all possible domain names to be encoded of course following the encoding rules of 4 however certain of course following the encoding rules of 4 however certain applications may restrict the set of valid characters and c are should applications may restrict the set of valid characters C are should be taken so that invalid characters in these contexts does not cause be taken so that invalid characters in these contexts does not cause harm In particular host names in the DNS have certain harm In particular host names in the DNS have certain restrictions It is up to these application to limit this subset restrictions It is up to these application to limit this subset this URI scheme places no restrictions this URI scheme places no restrictions Intended usage Whenever DNS resources are useful to reference by Intended usage Whenever DNS resources are useful to reference by protocol independent identifiers often when the data is more protocol independent identifiers often when the data is more important than the access method Since software in general has important than the access method Since software in general has coped without this so far it is not anticipated to be implemented coped without this so far it is not anticipated to be implemented widely nor migrated to by existing systems but specific solutions widely nor migrated to by existing systems but specific solutions skipping to change at page 7 line 5 skipping to change at page 8 line 11 2 2 Interaction with Binary Labels 11 or other extended label types Interaction with Binary Labels 11 or other extended label types has not been analyzed However they appear to be infrequently used has not been analyzed However they appear to be infrequently used in practice in practice Contact simon josefsson org Contact simon josefsson org Author Change Controller simon josefsson org Author Change Controller simon josefsson org 3 Examples 4 Examples A DNS URI is of the following general form This is intended to A DNS URI is of the following general form This is intended to illustrate not define the scheme illustrate not define the scheme dns authority domain CLASS class TYPE type dns authority domain CLASS class TYPE type The following illustrate a URI for a resource with the absolute name The following illustrate a URI for a resource with the absolute name www example org the Internet IN class and the Address A type www example org the Internet IN class and the Address A type dns www example org clAsS IN tYpE A dns www example org clAsS IN tYpE A skipping to change at page 7 line

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  •