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diff --git a/contrib/bind9/doc/rfc/rfc2163.txt b/contrib/bind9/doc/rfc/rfc2163.txt deleted file mode 100644 index 00fcee7..0000000 --- a/contrib/bind9/doc/rfc/rfc2163.txt +++ /dev/null @@ -1,1459 +0,0 @@ - - - - - - -Network Working Group C. Allocchio -Request for Comments: 2163 GARR-Italy -Obsoletes: 1664 January 1998 -Category: Standards Track - - - Using the Internet DNS to Distribute - MIXER Conformant Global Address Mapping (MCGAM) - -Status of this Memo - - This document specifies an Internet standards track protocol for the - Internet community, and requests discussion and suggestions for - improvements. Please refer to the current edition of the "Internet - Official Protocol Standards" (STD 1) for the standardization state - and status of this protocol. Distribution of this memo is unlimited. - -Copyright Notice - - Copyright (C) The Internet Society (1998). All Rights Reserved. - -Abstract - - This memo is the complete technical specification to store in the - Internet Domain Name System (DNS) the mapping information (MCGAM) - needed by MIXER conformant e-mail gateways and other tools to map - RFC822 domain names into X.400 O/R names and vice versa. Mapping - information can be managed in a distributed rather than a centralised - way. Organizations can publish their MIXER mapping or preferred - gateway routing information using just local resources (their local - DNS server), avoiding the need for a strong coordination with any - centralised organization. MIXER conformant gateways and tools located - on Internet hosts can retrieve the mapping information querying the - DNS instead of having fixed tables which need to be centrally updated - and distributed. - - This memo obsoletes RFC1664. It includes the changes introduced by - MIXER specification with respect to RFC1327: the new 'gate1' (O/R - addresses to domain) table is fully supported. Full backward - compatibility with RFC1664 specification is mantained, too. - - RFC1664 was a joint effort of IETF X400 operation working group - (x400ops) and TERENA (formely named "RARE") Mail and Messaging - working group (WG-MSG). This update was performed by the IETF MIXER - working group. - - - - - - -Allocchio Standards Track [Page 1] - -RFC 2163 MIXER MCGAM January 1998 - - -1. Introduction - - The connectivity between the Internet SMTP mail and other mail - services, including the Internet X.400 mail and the commercial X.400 - service providers, is assured by the Mail eXchanger (MX) record - information distributed via the Internet Domain Name System (DNS). A - number of documents then specify in details how to convert or encode - addresses from/to RFC822 style to the other mail system syntax. - However, only conversion methods provide, via some algorithm or a set - of mapping rules, a smooth translation, resulting in addresses - indistinguishable from the native ones in both RFC822 and foreign - world. - - MIXER describes a set of mappings (MIXER Conformant Global Address - Mapping - MCGAM) which will enable interworking between systems - operating the CCITT X.400 (1984/88/92) Recommendations and systems - using using the RFC822 mail protocol, or protocols derived from - RFC822. That document addresses conversion of services, addresses, - message envelopes, and message bodies between the two mail systems. - This document is concerned with one aspect of MIXER: the mechanism - for mapping between X.400 O/R addresses and RFC822 domain names. As - described in Appendix F of MIXER, implementation of the mappings - requires a database which maps between X.400 O/R addresses and domain - names; in RFC1327 this database was statically defined. - - The original approach in RFC1327 required many efforts to maintain - the correct mapping: all the gateways needed to get coherent tables - to apply the same mappings, the conversion tables had to be - distributed among all the operational gateways, and also every update - needed to be distributed. - - The concept of mapping rules distribution and use has been revised in - the new MIXER specification, introducing the concept of MIXER - Conformant Global Address Mapping (MCGAM). A MCGAM does not need to - be globally installed by any MIXER conformant gateway in the world - any more. However MIXER requires now efficient methods to publish its - MCGAM. - - Static tables are one of the possible methods to publish MCGAM. - However this static mechanism requires quite a long time to be spent - modifying and distributing the information, putting heavy constraints - on the time schedule of every update. In fact it does not appear - efficient compared to the Internet Domain Name Service (DNS). More - over it does not look feasible to distribute the database to a large - number of other useful applications, like local address converters, - e-mail User Agents or any other tool requiring the mapping rules to - produce correct results. - - - - -Allocchio Standards Track [Page 2] - -RFC 2163 MIXER MCGAM January 1998 - - - Two much more efficient methods are proposed by MIXER for publication - of MCGAM: the Internet DNS and X.500. This memo is the complete - technical specification for publishing MCGAM via Internet DNS. - - A first proposal to use the Internet DNS to store, retrieve and - maintain those mappings was introduced by two of the authors of - RFC1664 (B. Cole and R. Hagens) adopting two new DNS resource record - (RR) types: TO-X400 and TO-822. This proposal now adopts a more - complete strategy, and requires one new RR only. The distribution of - MCGAMs via DNS is in fact an important service for the whole Internet - community: it completes the information given by MX resource record - and it allows to produce clean addresses when messages are exchanged - among the Internet RFC822 world and the X.400 one (both Internet and - Public X.400 service providers). - - A first experiment in using the DNS without expanding the current set - of RR and using available ones was deployed by some of the authors of - RFC1664 at the time of its development. The existing PTR resource - records were used to store the mapping rules, and a new DNS tree was - created under the ".it" top level domain. The result of the - experiment was positive, and a few test applications ran under this - provisional set up. This test was also very useful in order to define - a possible migration strategy during the deployment of the new DNS - containing the new RR. The Internet DNS nameservers wishing to - provide this mapping information need in fact to be modified to - support the new RR type, and in the real Internet, due to the large - number of different implementations, this takes some time. - - The basic idea is to adopt a new DNS RR to store the mapping - information. The RFC822 to X.400 mapping rules (including the so - called 'gate2' rules) will be stored in the ordinary DNS tree, while - the definition of a new branch of the name space defined under each - national top level domain is envisaged in order to contain the X.400 - to RFC822 mappings ('table1' and 'gate1'). A "two-way" mapping - resolution schema is thus fully implemented. - - The creation of the new domain name space representing the X.400 O/R - names structure also provides the chance to use the DNS to distribute - dynamically other X.400 related information, thus solving other - efficiency problems currently affecting the X.400 MHS service. - - In this paper we will adopt the MCGAM syntax, showing how it can be - stored into the Internet DNS. - - - - - - - - -Allocchio Standards Track [Page 3] - -RFC 2163 MIXER MCGAM January 1998 - - -1.1 Definitions syntax - - The definitions in this document is given in BNF-like syntax, using - the following conventions: - - | means choice - \ is used for continuation of a definition over several lines - [] means optional - {} means repeated one or more times - - The definitions, however, are detailed only until a certain level, - and below it self-explaining character text strings will be used. - -2. Motivation - - Implementations of MIXER gateways require that a database store - address mapping information for X.400 and RFC822. This information - must be made available (published) to all MIXER gateways. In the - Internet community, the DNS has proven to be a practical mean for - providing a distributed name service. Advantages of using a DNS based - system over a table based approach for mapping between O/R addresses - and domain names are: - - - It avoids fetching and storing of entire mapping tables by every - host that wishes to implement MIXER gateways and/or tools - - - Modifications to the DNS based mapping information can be made - available in a more timely manner than with a table driven - approach. - - - It allows full authority delegation, in agreement with the - Internet regionalization process. - - - Table management is not necessarily required for DNS-based - MIXER gateways. - - - One can determine the mappings in use by a remote gateway by - querying the DNS (remote debugging). - - Also many other tools, like address converters and User Agents can - take advantage of the real-time availability of MIXER tables, - allowing a much easier maintenance of the information. - -3. The domain space for X.400 O/R name addresses - - Usual domain names (the ones normally used as the global part of an - RFC822 e-mail address) and their associated information, i.e., host - IP addresses, mail exchanger names, etc., are stored in the DNS as a - - - -Allocchio Standards Track [Page 4] - -RFC 2163 MIXER MCGAM January 1998 - - - distributed database under a number of top-level domains. Some top- - level domains are used for traditional categories or international - organisations (EDU, COM, NET, ORG, INT, MIL...). On the other hand - any country has its own two letter ISO country code as top-level - domain (FR, DE, GB, IT, RU, ...), including "US" for USA. The - special top-level/second-level couple IN-ADDR.ARPA is used to store - the IP address to domain name relationship. This memo defines in the - above structure the appropriate way to locate the X.400 O/R name - space, thus enabling to store in DNS the MIXER mappings (MCGAMs). - - The MIXER mapping information is composed by four tables: - - - 'table1' and 'gate1' gives the translation from X.400 to RFC822; - - 'table2' and 'gate2' tables map RFC822 into X.400. - - Each mapping table is composed by mapping rules, and a single mapping - rule is composed by a keyword (the argument of the mapping function - derived from the address to be translated) and a translator (the - mapping function parameter): - - keyword#translator# - - the '#' sign is a delimiter enclosing the translator. An example: - - foo.bar.us#PRMD$foo\.bar.ADMD$intx.C$us# - - Local mappings are not intended for use outside their restricted - environment, thus they should not be included in DNS. If local - mappings are used, they should be stored using static local tables, - exactly as local static host tables can be used with DNS. - - The keyword of a 'table2' and 'gate2' table entry is a valid RFC822 - domain; thus the usual domain name space can be used without problems - to store these entries. - On the other hand, the keyword of a 'table1' and 'gate1' entry - belongs to the X.400 O/R name space. The X.400 O/R name space does - not usually fit into the usual domain name space, although there are - a number of similarities; a new name structure is thus needed to - represent it. This new name structure contains the X.400 mail - domains. - - To ensure the correct functioning of the DNS system, the new X.400 - name structure must be hooked to the existing domain name space in a - way which respects the existing name hierarchy. - - A possible solution was to create another special branch, starting - from the root of the DNS tree, somehow similar to the in-addr.arpa - tree. This idea would have required to establish a central authority - - - -Allocchio Standards Track [Page 5] - -RFC 2163 MIXER MCGAM January 1998 - - - to coordinate at international level the management of each national - X.400 name tree, including the X.400 public service providers. This - coordination problem is a heavy burden if approached globally. More - over the X.400 name structure is very 'country oriented': thus while - it requires a coordination at national level, it does not have - concepts like the international root. In fact the X.400 international - service is based on a large number of bilateral agreements, and only - within some communities an international coordination service exists. - - The X.400 two letter ISO country codes, however, are the same used - for the RFC822 country top-level domains and this gives us an - appropriate hook to insert the new branches. The proposal is, in - fact, to create under each national top level ISO country code a new - branch in the name space. This branch represents exactly the X.400 - O/R name structure as defined in each single country, following the - ADMD, PRMD, O, OU hierarchy. A unique reserved label 'X42D' is placed - under each country top-level domain, and hence the national X.400 - name space derives its own structure: - - . (root) - | - +-----------------+-----------+--------+-----------------+... - | | | | - edu it us fr - | | | | - +---+---+... +-----+-----+... +-----+-----+... +--+---+... - | | | | | | | | | | - ... ... cnr X42D infn va ca X42D X42D inria - | | | | - +------------+------------+... ... ... +----+-------+... - | | | | | - ADMD-PtPostel ADMD-garr ADMD-Master400 ADMD-atlas ADMD-red - | | | | - +----------+----+... ... +-------+------+... ... - | | | | - PRMD-infn PRMD-STET PRMD-Telecom PRMD-Renault - | | | | - ... ... ... ... - - - The creation of the X.400 new name tree at national level solves the - problem of the international coordination. Actually the coordination - problem is just moved at national level, but it thus becomes easier - to solve. The coordination at national level between the X.400 - communities and the Internet world is already a requirement for the - creation of the national static MIXER mapping tables; the use of the - Internet DNS gives further motivations for this coordination. - - - - -Allocchio Standards Track [Page 6] - -RFC 2163 MIXER MCGAM January 1998 - - - The coordination at national level also fits in the new concept of - MCGAM pubblication. The DNS in fact allows a step by step authority - distribution, up to a final complete delegation: thus organizations - whishing to publish their MCGAM just need to receive delegation also - for their branch of the new X.400 name space. A further advantage of - the national based solution is to allow each country to set up its - own X.400 name structure in DNS and to deploy its own authority - delegation according to its local time scale and requirements, with - no loss of global service in the mean time. And last, placing the new - X.400 name tree and coordination process at national level fits into - the Internet regionalization and internationalisation process, as it - requires local bodies to take care of local coordination problems. - - The DNS name space thus contains completely the information required - by an e-mail gateway or tool to perform the X.400-RFC822 mapping: a - simple query to the nearest nameserver provides it. Moreover there is - no more any need to store, maintain and distribute manually any - mapping table. The new X.400 name space can also contain further - information about the X.400 community, as DNS allows for it a - complete set of resource records, and thus it allows further - developments. This set of RRs in the new X.400 name space must be - considered 'reserved' and thus not used until further specifications. - - The construction of the new domain space trees will follow the same - procedures used when organising at first the already existing DNS - space: at first the information will be stored in a quite centralised - way, and distribution of authority will be gradually achieved. A - separate document will describe the implementation phase and the - methods to assure a smooth introduction of the new service. - -4. The new DNS resource record for MIXER mapping rules: PX - - The specification of the Internet DNS (RFC1035) provides a number of - specific resource records (RRs) to contain specific pieces of - information. In particular they contain the Mail eXchanger (MX) RR - and the host Address (A) records which are used by the Internet SMTP - mailers. As we will store the RFC822 to X.400 mapping information in - the already existing DNS name tree, we need to define a new DNS RR in - order to avoid any possible clash or misuse of already existing data - structures. The same new RR will also be used to store the mappings - from X.400 to RFC822. More over the mapping information, i.e., the - MCGAMs, has a specific format and syntax which require an appropriate - data structure and processing. A further advantage of defining a new - RR is the ability to include flexibility for some eventual future - development. - - - - - - -Allocchio Standards Track [Page 7] - -RFC 2163 MIXER MCGAM January 1998 - - - The definition of the new 'PX' DNS resource record is: - - class: IN (Internet) - - name: PX (pointer to X.400/RFC822 mapping information) - - value: 26 - - The PX RDATA format is: - - +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ - | PREFERENCE | - +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ - / MAP822 / - / / - +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ - / MAPX400 / - / / - +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ - - where: - - PREFERENCE A 16 bit integer which specifies the preference given to - this RR among others at the same owner. Lower values - are preferred; - - MAP822 A <domain-name> element containing <rfc822-domain>, the - RFC822 part of the MCGAM; - - MAPX400 A <domain-name> element containing the value of - <x400-in-domain-syntax> derived from the X.400 part of - the MCGAM (see sect. 4.2); - - PX records cause no additional section processing. The PX RR format - is the usual one: - - <name> [<class>] [<TTL>] <type> <RDATA> - - When we store in DNS a 'table1' or a 'gate1' entry, then <name> will - be an X.400 mail domain name in DNS syntax (see sect. 4.2). When we - store a 'table2' or a 'gate2' table entry, <name> will be an RFC822 - mail domain name, including both fully qualified DNS domains and mail - only domains (MX-only domains). All normal DNS conventions, like - default values, wildcards, abbreviations and message compression, - apply also for all the components of the PX RR. In particular <name>, - MAP822 and MAPX400, as <domain-name> elements, must have the final - "." (root) when they are fully qualified. - - - - -Allocchio Standards Track [Page 8] - -RFC 2163 MIXER MCGAM January 1998 - - -4.1 Additional features of the PX resource record - - The definition of the RDATA for the PX resource record, and the fact - that DNS allows a distinction between an exact value and a wildcard - match for the <name> parameter, represent an extension of the MIXER - specification for mapping rules. In fact, any MCGAM entry is an - implicit wildcard entry, i.e., the rule - - net2.it#PRMD$net2.ADMD$p400.C$it# - - covers any RFC822 domain ending with 'net2.it', unless more detailed - rules for some subdomain in 'net2.it' are present. Thus there is no - possibility to specify explicitly a MCGAM as an exact match only - rule. In DNS an entry like - - *.net2.it. IN PX 10 net2.it. PRMD-net2.ADMD-p400.C-it. - - specify the usual wildcard match as for MIXER tables. However an - entry like - - ab.net2.it. IN PX 10 ab.net2.it. O-ab.PRMD-net2.ADMDb.C-it. - - is valid only for an exact match of 'ab.net2.it' RFC822 domain. - - Note also that in DNS syntax there is no '#' delimiter around MAP822 - and MAPX400 fields: the syntax defined in sect. 4.2 in fact does not - allow the <blank> (ASCII decimal 32) character within these fields, - making unneeded the use of an explicit delimiter as required in the - MIXER original syntax. - - Another extension to the MIXER specifications is the PREFERENCE value - defined as part of the PX RDATA section. This numeric value has - exactly the same meaning than the similar one used for the MX RR. It - is thus possible to specify more than one single mapping for a domain - (both from RFC822 to X.400 and vice versa), giving as the preference - order. In MIXER static tables, however, you cannot specify more than - one mapping per each RFC822 domain, and the same restriction apply - for any X.400 domain mapping to an RFC822 one. - - More over, in the X.400 recommendations a note suggests than an - ADMD=<blank> should be reserved for some special cases. Various - national functional profile specifications for an X.400 MHS states - that if an X.400 PRMD is reachable via any of its national ADMDs, - independently of its actual single or multiple connectivity with - them, it should use ADMD=<blank> to advertise this fact. Again, if a - PRMD has no connections to any ADMD it should use ADMD=0 to notify - its status, etc. However, in most of the current real situations, the - ADMD service providers do not accept messages coming from their - - - -Allocchio Standards Track [Page 9] - -RFC 2163 MIXER MCGAM January 1998 - - - subscribers if they have a blank ADMD, forcing them to have their own - ADMD value. In such a situation there are problems in indicating - properly the actually working mappings for domains with multiple - connectivity. The PX RDATA 'PREFERENCE' extension was introduced to - take in consideration these problems. - - However, as these extensions are not available with MIXER static - tables, it is strongly discouraged to use them when interworking with - any table based gateway or application. The extensions were in fact - introduced just to add more flexibility, like the PREFERENCE value, - or they were already implicit in the DNS mechanism, like the - wildcard specification. They should be used very carefully or just - considered 'reserved for future use'. In particular, for current use, - the PREFERENCE value in the PX record specification should be fixed - to a value of 50, and only wildcard specifications should be used - when specifying <name> values. - -4.2 The DNS syntax for an X.400 'domain' - - The syntax definition of the MCGAM rules is defined in appendix F of - that document. However that syntax is not very human oriented and - contains a number of characters which have a special meaning in other - fields of the Internet DNS. Thus in order to avoid any possible - problem, especially due to some old DNS implementations still being - used in the Internet, we define a syntax for the X.400 part of any - MCGAM rules (and hence for any X.400 O/R name) which makes it - compatible with a <domain-name> element, i.e., - - <domain-name> ::= <subdomain> | " " - <subdomain> ::= <label> | <label> "." <subdomain> - <label> ::= <alphanum>| - <alphanum> {<alphanumhyphen>} <alphanum> - <alphanum> ::= "0".."9" | "A".."Z" | "a".."z" - <alphanumhyphen> ::= "0".."9" | "A".."Z" | "a".."z" | "-" - - (see RFC1035, section 2.3.1, page 8). The legal character set for - <label> does not correspond to the IA5 Printablestring one used in - MIXER to define MCGAM rules. However a very simple "escape mechanism" - can be applied in order to bypass the problem. We can in fact simply - describe the X.400 part of a MCGAM rule format as: - - <map-rule> ::= <map-elem> | <map-elem> { "." <map-elem> } - <map-elem> ::= <attr-label> "$" <attr-value> - <attr-label> ::= "C" | "ADMD" | "PRMD" | "O" | "OU" - <attr-value> ::= " " | "@" | IA5-Printablestring - - - - - - -Allocchio Standards Track [Page 10] - -RFC 2163 MIXER MCGAM January 1998 - - - As you can notice <domain-name> and <map-rule> look similar, and also - <label> and <map-elem> look the same. If we define the correct method - to transform a <map-elem> into a <label> and vice versa the problem - to write a MCGAM rule in <domain-name> syntax is solved. - - The RFC822 domain part of any MCGAM rule is of course already in - <domain-name> syntax, and thus remains unchanged. - - In particular, in a 'table1' or 'gate1' mapping rule the 'keyword' - value must be converted into <x400-in-domain-syntax> (X.400 mail DNS - mail domain), while the 'translator' value is already a valid RFC822 - domain. Vice versa in a 'table2' or 'gate2' mapping rule, the - 'translator' must be converted into <x400-in-domain-syntax>, while - the 'keyword' is already a valid RFC822 domain. - -4.2.1 IA5-Printablestring to <alphanumhyphen> mappings - - The problem of unmatching IA5-Printablestring and <label> character - set definition is solved by a simple character mapping rule: whenever - an IA5 character does not belong to <alphanumhyphen>, then it is - mapped using its 3 digit decimal ASCII code, enclosed in hyphens. A - small set of special rules is also defined for the most frequent - cases. Moreover some frequent characters combinations used in MIXER - rules are also mapped as special cases. - - Let's then define the following simple rules: - - MCGAM rule DNS store translation conditions - ----------------------------------------------------------------- - <attr-label>$@ <attr-label> missing attribute - <attr-label>$<blank> <attr-label>"b" blank attribute - <attr-label>$xxx <attr-label>-xxx elsewhere - - Non <alphanumhyphen> characters in <attr-value>: - - MCGAM rule DNS store translation conditions - ----------------------------------------------------------------- - - -h- hyphen - \. -d- quoted dot - <blank> -b- blank - <non A/N character> -<3digit-decimal>- elsewhere - - If the DNS store translation of <attr-value> happens to end with an - hyphen, then this last hyphen is omitted. - - Let's now have some examples: - - - - - -Allocchio Standards Track [Page 11] - -RFC 2163 MIXER MCGAM January 1998 - - - MCGAM rule DNS store translation conditions - ----------------------------------------------------------------- - PRMD$@ PRMD missing attribute - ADMD$<blank> ADMDb blank attribute - ADMD$400-net ADMD-400-h-net hyphen mapping - PRMD$UK\.BD PRMD-UK-d-BD quoted dot mapping - O$ACME Inc\. O-ACME-b-Inc-d blank & final hyphen - PRMD$main-400-a PRMD-main-h-400-h-a hyphen mapping - O$-123-b O--h-123-h-b hyphen mapping - OU$123-x OU-123-h-x hyphen mapping - PRMD$Adis+co PRMD-Adis-043-co 3digit mapping - - Thus, an X.400 part from a MCGAM like - - OU$uuu.O$@.PRMD$ppp\.rrr.ADMD$aaa ddd-mmm.C$cc - - translates to - - OU-uuu.O.PRMD-ppp-d-rrr.ADMD-aaa-b-ddd-h-mmm.C-cc - - Another example: - - OU$sales dept\..O$@.PRMD$ACME.ADMD$ .C$GB - - translates to - - OU-sales-b-dept-d.O.PRMD-ACME.ADMDb.C-GB - -4.2.2 Flow chart - - In order to achieve the proper DNS store translations of the X.400 - part of a MCGAM or any other X.400 O/R name, some software tools will - be used. It is in fact evident that the above rules for converting - mapping table from MIXER to DNS format (and vice versa) are not user - friendly enough to think of a human made conversion. - - To help in designing such tools, we describe hereunder a small flow - chart. The fundamental rule to be applied during translation is, - however, the following: - - "A string must be parsed from left to right, moving appropriately - the pointer in order not to consider again the already translated - left section of the string in subsequent analysis." - - - - - - - - -Allocchio Standards Track [Page 12] - -RFC 2163 MIXER MCGAM January 1998 - - - Flow chart 1 - Translation from MIXER to DNS format: - - parse single attribute - (enclosed in "." separators) - | - (yes) --- <label>$@ ? --- (no) - | | - map to <label> (no) <label>$<blank> ? (yes) - | | | - | map to <label>- map to <label>"b" - | | | - | map "\." to -d- | - | | | - | map "-" to -h- | - | | | - | map non A/N char to -<3digit>- | - restart | | | - ^ | remove (if any) last "-" | - | | | | - | \-------> add a "." <--------------/ - | | - \---------- take next attribute (if any) - - - Flow chart 2 - Translation from DNS to MIXER format: - - - parse single attribute - (enclosed in "." separators) - | - (yes) ---- <label> ? ---- (no) - | | - map to <label>$@ (no) <label>"b" ? (yes) - | | | - | map to <label>$ map to <label>$<blank> - | | | - | map -d- to "\." | - | | | - | map -h- to "-" | - | | | - | map -b- to " " | - restart | | | - ^ | map -<3digit>- to non A/N char | - | | | | - | \--------> add a "." <----------/ - | | - \------------- take next attribute (if any) - - - - -Allocchio Standards Track [Page 13] - -RFC 2163 MIXER MCGAM January 1998 - - - Note that the above flow charts deal with the translation of the - attributes syntax, only. - -4.2.3 The Country Code convention in the <name> value. - - The RFC822 domain space and the X.400 O/R address space, as said in - section 3, have one specific common feature: the X.400 ISO country - codes are the same as the RFC822 ISO top level domains for countries. - In the previous sections we have also defined a method to write in - <domain-name> syntax any X.400 domain, while in section 3 we - described the new name space starting at each country top level - domain under the X42D.cc (where 'cc' is then two letter ISO country - code). - - The <name> value for a 'table1' or 'gate1' entry in DNS should thus - be derived from the X.400 domain value, translated to <domain-name> - syntax, adding the 'X42D.cc.' post-fix to it, i.e., - - ADMD$acme.C$fr - - produces in <domain-name> syntax the key: - - ADMD-acme.C-fr - - which is post-fixed by 'X42D.fr.' resulting in: - - ADMD-acme.C-fr.X42D.fr. - - However, due to the identical encoding for X.400 country codes and - RFC822 country top level domains, the string 'C-fr.X42D.fr.' is - clearly redundant. - - We thus define the 'Country Code convention' for the <name> key, - i.e., - - "The C-cc section of an X.400 domain in <domain-name> syntax must - be omitted when creating a <name> key, as it is identical to the - top level country code used to identify the DNS zone where the - information is stored". - - Thus we obtain the following <name> key examples: - - X.400 domain DNS <name> key - -------------------------------------------------------------------- - ADMD$acme.C$fr ADMD-acme.X42D.fr. - PRMD$ux\.av.ADMD$ .C$gb PRMD-ux-d-av.ADMDb.X42D.gb. - PRMD$ppb.ADMD$Dat 400.C$de PRMD-ppb.ADMD-Dat-b-400.X42D.de. - - - - -Allocchio Standards Track [Page 14] - -RFC 2163 MIXER MCGAM January 1998 - - -4.3 Creating the appropriate DNS files - - Using MIXER's assumption of an asymmetric mapping between X.400 and - RFC822 addresses, two separate relations are required to store the - mapping database: MIXER 'table1' and MIXER 'table2'; thus also in DNS - we will maintain the two different sections, even if they will both - use the PX resource record. More over MIXER also specify two - additional tables: MIXER 'gate1' and 'gate2' tables. These additional - tables, however, have the same syntax rules than MIXER 'table1' and - 'table2' respectively, and thus the same translation procedure as - 'table1' and 'table2' will be applied; some details about the MIXER - 'gate1' and 'gate2' tables are discussed in section 4.4. - - Let's now check how to create, from an MCGAM entry, the appropriate - DNS entry in a DNS data file. We can again define an MCGAM entry as - defined in appendix F of that document as: - - <x400-domain>#<rfc822-domain># (case A: 'table1' and 'gate1' - entry) - - and - - <rfc822-domain>#<x400-domain># (case B: 'table2' and 'gate2' - entry) - - The two cases must be considered separately. Let's consider case A. - - - take <x400-domain> and translate it into <domain-name> syntax, - obtaining <x400-in-domain-syntax>; - - create the <name> key from <x400-in-domain-syntax> i.e., apply - the Country Code convention described in sect. 4.2.3; - - construct the DNS PX record as: - - *.<name> IN PX 50 <rfc822-domain> <x400-in-domain-syntax> - - Please note that within PX RDATA the <rfc822-domain> precedes the - <x400-in-domain-syntax> also for a 'table1' and 'gate1' entry. - - an example: from the 'table1' rule - - PRMD$ab.ADMD$ac.C$fr#ab.fr# - - we obtain - - *.PRMD-ab.ADMD-ac.X42D.fr. IN PX 50 ab.fr. PRMD-ab.ADMD-ac.C-fr. - - Note that <name>, <rfc822-domain> and <x400-in-domain-syntax> are - fully qualified <domain-name> elements, thus ending with a ".". - - - -Allocchio Standards Track [Page 15] - -RFC 2163 MIXER MCGAM January 1998 - - - Let's now consider case B. - - - take <rfc822-domain> as <name> key; - - translate <x400-domain> into <x400-in-domain-syntax>; - - construct the DNS PX record as: - - *.<name> IN PX 50 <rfc822-domain> <x400-in-domain-syntax> - - an example: from the 'table2' rule - - ab.fr#PRMD$ab.ADMD$ac.C$fr# - - we obtain - - *.ab.fr. IN PX 50 ab.fr. PRMD-ab.ADMD-ac.C-fr. - - Again note the fully qualified <domain-name> elements. - - A file containing the MIXER mapping rules and MIXER 'gate1' and - 'gate2' table written in DNS format will look like the following - fictious example: - - ! - ! MIXER table 1: X.400 --> RFC822 - ! - *.ADMD-acme.X42D.it. IN PX 50 it. ADMD-acme.C-it. - *.PRMD-accred.ADMD-tx400.X42D.it. IN PX 50 \ - accred.it. PRMD-accred.ADMD-tx400.C-it. - *.O-u-h-newcity.PRMD-x4net.ADMDb.X42D.it. IN PX 50 \ - cs.ncty.it. O-u-h-newcity.PRMD-x4net.ADMDb.C-it. - ! - ! MIXER table 2: RFC822 --> X.400 - ! - *.nrc.it. IN PX 50 nrc.it. PRMD-nrc.ADMD-acme.C-it. - *.ninp.it. IN PX 50 ninp.it. O.PRMD-ninp.ADMD-acme.C-it. - *.bd.it. IN PX 50 bd.it. PRMD-uk-d-bd.ADMDb.C-it. - ! - ! MIXER Gate 1 Table - ! - *.ADMD-XKW-h-Mail.X42D.it. IN PX 50 \ - XKW-gateway.it. ADMD-XKW-h-Mail.C-it.G. - *.PRMD-Super-b-Inc.ADMDb.X42D.it. IN PX 50 \ - GlobalGw.it. PRMD-Super-b-Inc.ADMDb.C-it.G. - ! - ! MIXER Gate 2 Table - ! - my.it. IN PX 50 my.it. OU-int-h-gw.O.PRMD-ninp.ADMD-acme.C-it.G. - co.it. IN PX 50 co.it. O-mhs-h-relay.PRMD-x4net.ADMDb.C-it.G. - - - -Allocchio Standards Track [Page 16] - -RFC 2163 MIXER MCGAM January 1998 - - - (here the "\" indicates continuation on the same line, as wrapping is - done only due to typographical reasons). - - Note the special suffix ".G." on the right side of the 'gate1' and - 'gate2' Tables section whose aim is described in section 4.4. The - corresponding MIXER tables are: - - # - # MIXER table 1: X.400 --> RFC822 - # - ADMD$acme.C$it#it# - PRMD$accred.ADMD$tx400.C$it#accred.it# - O$u-newcity.PRMD$x4net.ADMD$ .C$it#cs.ncty.it# - # - # MIXER table 2: RFC822 --> X.400 - # - nrc.it#PRMD$nrc.ADMD$acme.C$it# - ninp.it#O.PRMD$ninp.ADMD$acme.C$it# - bd.it#PRMD$uk\.bd.ADMD$ .C$it# - # - # MIXER Gate 1 Table - # - ADMD$XKW-Mail.C$it#XKW-gateway.it# - PRMD$Super Inc.ADMD$ .C$it#GlobalGw.it# - # - # MIXER Gate 2 Table - # - my.it#OU$int-gw.O$@.PRMD$ninp.ADMD$acme.C$it# - co.it#O$mhs-relay.PRMD$x4net.ADMD$ .C$t# - -4.4 Storing the MIXER 'gate1' and 'gate2' tables - - Section 4.3.4 of MIXER also specify how an address should be - converted between RFC822 and X.400 in case a complete mapping is - impossible. To allow the use of DDAs for non mappable domains, the - MIXER 'gate2' table is thus introduced. - - In a totally similar way, when an X.400 address cannot be completely - converted in RFC822, section 4.3.5 of MIXER specifies how to encode - (LHS encoding) the address itself, pointing then to the appropriate - MIXER conformant gateway, indicated in the MIXER 'gate1' table. - - DNS must store and distribute also these 'gate1' and 'gate2' data. - - One of the major features of the DNS is the ability to distribute the - authority: a certain site runs the "primary" nameserver for one - determined sub-tree and thus it is also the only place allowed to - update information regarding that sub-tree. This fact allows, in our - - - -Allocchio Standards Track [Page 17] - -RFC 2163 MIXER MCGAM January 1998 - - - case, a further additional feature to the table based approach. In - fact we can avoid one possible ambiguity about the use of the 'gate1' - and 'gate2' tables (and thus of LHS and DDAs encoding). - - The authority maintaining a DNS entry in the usual RFC822 domain - space is the only one allowed to decide if its domain should be - mapped using Standard Attributes (SA) syntax or Domain Defined - Attributes (DDA) one. If the authority decides that its RFC822 domain - should be mapped using SA, then the PX RDATA will be a 'table2' - entry, otherwise it will be a 'gate2' table entry. Thus for an RFC822 - domain we cannot have any more two possible entries, one from 'table2 - and another one from 'gate2' table, and the action for a gateway - results clearly stated. - - Similarly, the authority mantaining a DNS entry in the new X.400 name - space is the only one allowed to decide if its X.400 domain should be - mapped using SA syntax or Left Hand Side (LHS) encoding. If the - authority decides that its X.400 domain should be mapped using SA, - then the PX RDATA will be a 'table1' entry, otherwise it will be a - 'gate1' table entry. Thus also for an X.400 domain we cannot have any - more two possible entries, one from 'table1' and another one from - 'gate1' table, and the action for a gateway results clearly stated. - - The MIXER 'gate1' table syntax is actually identical to MIXER - 'table1', and 'gate2' table syntax is identical to MIXER 'table2'. - Thus the same syntax translation rules from MIXER to DNS format can - be applied in both cases. However a gateway or any other application - must know if the answer it got from DNS contains some 'table1', - 'table2' or some 'gate1', 'gate2' table information. This is easily - obtained flagging with an additional ".G." post-fix the PX RDATA - value when it contains a 'gate1' or 'gate2' table entry. The example - in section 4.3 shows clearly the result. As any X.400 O/R domain must - end with a country code ("C-xx" in our DNS syntax) the additional - ".G." creates no conflicts or ambiguities at all. This postfix must - obviously be removed before using the MIXER 'gate1' or 'gate2' table - data. - -5. Finding MIXER mapping information from DNS - - The MIXER mapping information is stored in DNS both in the normal - RFC822 domain name space, and in the newly defined X.400 name space. - The information, stored in PX resource records, does not represent a - full RFC822 or X.400 O/R address: it is a template which specifies - the fields of the domain that are used by the mapping algorithm. - - When mapping information is stored in the DNS, queries to the DNS are - issued whenever an iterative search through the mapping table would - be performed (MIXER: section 4.3.4, State I; section 4.3.5, mapping - - - -Allocchio Standards Track [Page 18] - -RFC 2163 MIXER MCGAM January 1998 - - - B). Due to the DNS search mechanism, DNS by itself returns the - longest possible match in the stored mapping rule with a single - query, thus no iteration and/or multiple queries are needed. As - specified in MIXER, a search of the mapping table will result in - either success (mapping found) or failure (query failed, mapping not - found). - - When a DNS query is issued, a third possible result is timeout. If - the result is timeout, the gateway operation is delayed and then - retried at a later time. A result of success or failure is processed - according to the algorithms specified in MIXER. If a DNS error code - is returned, an error message should be logged and the gateway - operation is delayed as for timeout. These pathological situations, - however, should be avoided with a careful duplication and chaching - mechanism which DNS itself provides. - - Searching the nameserver which can authoritatively solve the query is - automatically performed by the DNS distributed name service. - -5.1 A DNS query example - - An MIXER mail-gateway located in the Internet, when translating - addresses from RFC822 to X.400, can get information about the MCGAM - rule asking the DNS. As an example, when translating the address - SUN.CCE.NRC.IT, the gateway will just query DNS for the associated PX - resource record. The DNS should contain a PX record like this: - - *.cce.nrc.it. IN PX 50 cce.nrc.it. O-cce.PRMD-nrc.ADMD-acme.C-it. - - The first query will return immediately the appropriate mapping rule - in DNS store format. - - There is no ".G." at the end of the obtained PX RDATA value, thus - applying the syntax translation specified in paragraph 4.2 the MIXER - Table 2 mapping rule will be obtained. - - Let's now take another example where a 'gate2' table rule is - returned. If we are looking for an RFC822 domain ending with top - level domain "MW", and the DNS contains a PX record like this, - - *.mw. IN PX 50 mw. O-cce.PRMD-nrc.ADMD-acme.C-it.G. - - DNS will return 'mw.' and 'O-cce.PRMD-nrc.ADMD-acme.C-it.G.', i.e., a - 'gate2' table entry in DNS store format. Dropping the final ".G." and - applying the syntax translation specified in paragraph 4.2 the - original rule will be available. More over, the ".G." flag also tells - the gateway to use DDA encoding for the inquired RFC822 domain. - - - - -Allocchio Standards Track [Page 19] - -RFC 2163 MIXER MCGAM January 1998 - - - On the other hand, translating from X.400 to RFC822 the address - - C=de; ADMD=pkz; PRMD=nfc; O=top; - - the mail gateway should convert the syntax according to paragraph - 4.2, apply the 'Country code convention' described in 4.2.3 to derive - the appropriate DNS translation of the X.400 O/R name and then query - DNS for the corresponding PX resource record. The obtained record for - which the PX record must be queried is thus: - - O-top.PRMD-nfc.ADMD-pkz.X42D.de. - - The DNS could contain: - - *.ADMD-pkz.X42D.de. IN PX 50 pkz.de. ADMD-pkz.C-de. - - Assuming that there are not more specific records in DNS, the - wildcard mechanism will return the MIXER 'table1' rule in encoded - format. - - Finally, an example where a 'gate1' rule is involved. If we are - looking for an X.400 domain ending with ADMD=PWT400; C=US; , and the - DNS contains a PX record like this, - - *.ADMD-PWT400.X42D.us. IN PX 50 intGw.com. ADMD-PWT400.C-us.G. - - DNS will return 'intGw.com.' and 'ADMD-PWT400.C-us.G.', i.e., a - 'gate1' table entry in DNS store format. Dropping the final ".G." and - applying the syntax translation specified in paragraph 4.2 the - original rule will be available. More over, the ".G." flag also tells - the gateway to use LHS encoding for the inquired X.400 domain. - -6. Administration of mapping information - - The DNS, using the PX RR, is able to distribute the MCGAM rules to - all MIXER gateways located on the Internet. However, not all MIXER - gateways will be able to use the Internet DNS. It is expected that - some gateways in a particular management domain will conform to one - of the following models: - - (a) Table-based, (b) DNS-based, (c) X.500-based - - Table-based management domains will continue to publish their MCGAM - rules and retrieve the mapping tables via the International Mapping - Table coordinator, manually or via some automated procedures. Their - MCGAM information can be made available also in DNS by the - appropriate DNS authorities, using the same mechanism already in - place for MX records: if a branch has not yet in place its own DNS - - - -Allocchio Standards Track [Page 20] - -RFC 2163 MIXER MCGAM January 1998 - - - server, some higher authority in the DNS tree will provide the - service for it. A transition procedure similar to the one used to - migrate from the 'hosts.txt' tables to DNS can be applied also to the - deployment phase of this specification. An informational document - describing the implementation phase and the detailed coordination - procedures is expected. - - Another distributed directory service which can distribute the MCGAM - information is X.500. Coordination with table-based domains can be - obtained in an identical way as for the DNS case. - - Coordination of MCGAM information between DNS and X.500 is more - complex, as it requies some kind of uploading information between the - two systems. The ideal solution is a dynamic alignment mechanism - which transparently makes the DNS mapping information available in - X.500 and vice versa. Some work in this specific field is already - being done [see Costa] which can result in a global transparent - directory service, where the information is stored in DNS or in - X.500, but is visible completely by any of the two systems. - - However we must remind that MIXER concept of MCGAM rules publication - is different from the old RFC1327 concept of globally distributed, - coordinated and unique mapping rules. In fact MIXER does not requires - any more for any conformant gateway or tool to know the complete set - of MCGAM: it only requires to use some set (eventually empty) of - valid MCGAM rules, published either by Tables, DNS or X.500 - mechanisms or any combination of these methods. More over MIXER - specifies that also incomplete sets of MCGAM can be used, and - supplementary local unpublished (but valid) MCGAM can also be used. - As a consequence, the problem of coordination between the three - systems proposed by MIXER for MCGAM publication is non essential, and - important only for efficient operational matters. It does not in fact - affect the correct behaviour of MIXER conformant gateways and tools. - -7. Conclusion - - The introduction of the new PX resource record and the definition of - the X.400 O/R name space in the DNS structure provide a good - repository for MCGAM information. The mapping information is stored - in the DNS tree structure so that it can be easily obtained using the - DNS distributed name service. At the same time the definition of the - appropriate DNS space for X.400 O/R names provide a repository where - to store and distribute some other X.400 MHS information. The use of - the DNS has many known advantages in storing, managing and updating - the information. A successful number of tests were been performed - under the provisional top level domain "X400.IT" when RFC1664 was - developed, and their results confirmed the advantages of the method. - Operational exeprience for over 2 years with RFC1664 specification - - - -Allocchio Standards Track [Page 21] - -RFC 2163 MIXER MCGAM January 1998 - - - confirmed the feasibility of the method, and helped identifying some - operational procedures to deploy the insertion of MCGAM into DNS. - - Software to query the DNS and then to convert between the textual - representation of DNS resource records and the address format defined - in MIXER was developed with RFC1664. This software also allows a - smooth implementation and deployment period, eventually taking care - of the transition phase. This software can be easily used (with - little or null modification) also for this updated specification, - supporting the new 'gate1' MIXER table. DNS software implementations - supporting RFC1664 also supports with no modification this memo new - specification. - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -Allocchio Standards Track [Page 22] - -RFC 2163 MIXER MCGAM January 1998 - - - A further informational document describing operational and - implementation of the service is expected. - -8. Acknowledgements - - We wish to thanks all those who contributed to the discussion and - revision of this document: many of their ideas and suggestions - constitute essential parts of this work. In particular thanks to Jon - Postel, Paul Mockapetris, Rob Austin and the whole IETF x400ops, - TERENA wg-msg and IETF namedroppers groups. A special mention to - Christian Huitema for his fundamental contribution to this work. - - This document is a revision of RFC1664, edited by one of its authors - on behalf of the IETF MIXER working group. The current editor wishes - to thank here also the authors of RFC1664: - - Antonio Blasco Bonito RFC822: bonito@cnuce.cnr.it - CNUCE - CNR X.400: C=it;A=garr;P=cnr; - Reparto infr. reti O=cnuce;S=bonito; - Viale S. Maria 36 - I 56126 Pisa - Italy - - - Bruce Cole RFC822: bcole@cisco.com - Cisco Systems Inc. X.400: C=us;A= ;P=Internet; - P.O. Box 3075 DD.rfc-822=bcole(a)cisco.com; - 1525 O'Brien Drive - Menlo Park, CA 94026 - U.S.A. - - - Silvia Giordano RFC822: giordano@cscs.ch - Centro Svizzero di X.400: C=ch;A=arcom;P=switch;O=cscs; - Calcolo Scientifico S=giordano; - Via Cantonale - CH 6928 Manno - Switzerland - - - Robert Hagens RFC822: hagens@ans.net - Advanced Network and Services X.400: C=us;A= ;P=Internet; - 1875 Campus Commons Drive DD.rfc-822=hagens(a)ans.net; - Reston, VA 22091 - U.S.A. - - - - - - -Allocchio Standards Track [Page 23] - -RFC 2163 MIXER MCGAM January 1998 - - -9. References - - [CCITT] CCITT SG 5/VII, "Recommendation X.400, Message Handling - Systems: System Model - Service Elements", October 1988. - - [RFC 1327] Kille, S., "Mapping between X.400(1988)/ISO 10021 and RFC - 822", RFC 1327, March 1992. - - [RFC 1034] Mockapetris, P., "Domain Names - Concepts and Facilities", - STD 13, RFC 1034, USC/Information Sciences Institute, November - 1987. - - [RFC 1035] Mockapetris, P., "Domain names - Implementation and - Specification", STD 13, RFC 1035, USC/Information Sciences - Institute, November 1987. - - [RFC 1033] Lottor, M., "Domain Administrators Operation Guide", RFC - 1033, SRI International, November 1987. - - [RFC 2156] Kille, S. E., " MIXER (Mime Internet X.400 Enhanced - Relay): Mapping between X.400 and RFC 822/MIME", RFC 2156, - January 1998. - - [Costa] Costa, A., Macedo, J., and V. Freitas, "Accessing and - Managing DNS Information in the X.500 Directory", Proceeding of - the 4th Joint European Networking Conference, Trondheim, NO, May - 1993. - -10. Security Considerations - - This document specifies a means by which DNS "PX" records can direct - the translation between X.400 and Internet mail addresses. - - This can indirectly affect the routing of mail across an gateway - between X.400 and Internet Mail. A succesful attack on this service - could cause incorrect translation of an originator address (thus - "forging" the originator address), or incorrect translation of a - recipient address (thus directing the mail to an unauthorized - recipient, or making it appear to an authorized recipient, that the - message was intended for recipients other than those chosen by the - originator) or could force the mail path via some particular gateway - or message transfer agent where mail security can be affected by - compromised software. - - - - - - - - -Allocchio Standards Track [Page 24] - -RFC 2163 MIXER MCGAM January 1998 - - - There are several means by which an attacker might be able to deliver - incorrect PX records to a client. These include: (a) compromise of a - DNS server, (b) generating a counterfeit response to a client's DNS - query, (c) returning incorrect "additional information" in response - to an unrelated query. - - Clients using PX records SHOULD ensure that routing and address - translations are based only on authoritative answers. Once DNS - Security mechanisms [RFC 2065] become more widely deployed, clients - SHOULD employ those mechanisms to verify the authenticity and - integrity of PX records. - -11. Author's Address - - Claudio Allocchio - Sincrotrone Trieste - SS 14 Km 163.5 Basovizza - I 34012 Trieste - Italy - - RFC822: Claudio.Allocchio@elettra.trieste.it - X.400: C=it;A=garr;P=Trieste;O=Elettra; - S=Allocchio;G=Claudio; - Phone: +39 40 3758523 - Fax: +39 40 3758565 - - - - - - - - - - - - - - - - - - - - - - - - - - -Allocchio Standards Track [Page 25] - -RFC 2163 MIXER MCGAM January 1998 - - -12. Full Copyright Statement - - Copyright (C) The Internet Society (1998). All Rights Reserved. - - This document and translations of it may be copied and furnished to - others, and derivative works that comment on or otherwise explain it - or assist in its implementation may be prepared, copied, published - and distributed, in whole or in part, without restriction of any - kind, provided that the above copyright notice and this paragraph are - included on all such copies and derivative works. However, this - document itself may not be modified in any way, such as by removing - the copyright notice or references to the Internet Society or other - Internet organizations, except as needed for the purpose of - developing Internet standards in which case the procedures for - copyrights defined in the Internet Standards process must be - followed, or as required to translate it into languages other than - English. - - The limited permissions granted above are perpetual and will not be - revoked by the Internet Society or its successors or assigns. - - This document and the information contained herein is provided on an - "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING - TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING - BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION - HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF - MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. - - - - - - - - - - - - - - - - - - - - - - - - -Allocchio Standards Track [Page 26] - |
