rfc1034.2up.ps

this gives details of the network programming

/fname (/usr/local/share/doc/rfc/Mirrors/ftp.isi.edu/in-notes/rfc1034.txt) def
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(RFC 1034             Domain Concepts and Facilities        November 1987) s
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(RDATA           which is the type and sometimes class dependent data) s
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(                which describes the resource:) s
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(                A               For the IN class, a 32 bit IP address) s
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(                                For the CH class, a domain name followed) s
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(                                by a 16 bit octal Chaos address.) s
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(                CNAME           a domain name.) s
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(                MX              a 16 bit preference value \(lower is) s
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(                                better\) followed by a host name willing) s
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(                                to act as a mail exchange for the owner) s
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(                                domain.) s
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(                NS              a host name.) s
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(                PTR             a domain name.) s
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(                SOA             several fields.) s
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(The owner name is often implicit, rather than forming an integral part) s
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(of the RR.  For example, many name servers internally form tree or hash) s
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(structures for the name space, and chain RRs off nodes.  The remaining) s
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(RR parts are the fixed header \(type, class, TTL\) which is consistent for) s
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(all RRs, and a variable part \(RDATA\) that fits the needs of the resource) s
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(being described.) s
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(The meaning of the TTL field is a time limit on how long an RR can be) s
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(kept in a cache.  This limit does not apply to authoritative data in) s
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(zones; it is also timed out, but by the refreshing policies for the) s
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(zone.  The TTL is assigned by the administrator for the zone where the) s
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(data originates.  While short TTLs can be used to minimize caching, and) s
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(a zero TTL prohibits caching, the realities of Internet performance) s
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(suggest that these times should be on the order of days for the typical) s
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(host.  If a change can be anticipated, the TTL can be reduced prior to) s
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(the change to minimize inconsistency during the change, and then) s
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(increased back to its former value following the change.) s
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(The data in the RDATA section of RRs is carried as a combination of) s
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(binary strings and domain names.  The domain names are frequently used) s
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(as "pointers" to other data in the DNS.) s
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(3.6.1. Textual expression of RRs) s
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(RRs are represented in binary form in the packets of the DNS protocol,) s
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(and are usually represented in highly encoded form when stored in a name) s
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(server or resolver.  In this memo, we adopt a style similar to that used) s
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(Mockapetris                                                    [Page 13]) s
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/pagenum 14 def
/fname (/usr/local/share/doc/rfc/Mirrors/ftp.isi.edu/in-notes/rfc1034.txt) def
/fdir (/usr/local/share/doc/rfc/Mirrors/ftp.isi.edu/in-notes/) def
/ftail (rfc1034.txt) def
% User defined strings:
/fmodstr (Tue Nov 24 00:00:00 1987) def
/pagenumstr (14) def
/user_header_p true def
/user_header_left_str (RFC1034) def
/user_header_center_str (RFC.net) def
/user_header_right_str (Page 14 of 56) def
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(RFC 1034             Domain Concepts and Facilities        November 1987) s
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(in master files in order to show the contents of RRs.  In this format,) s
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(most RRs are shown on a single line, although continuation lines are) s
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(possible using parentheses.) s
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(The start of the line gives the owner of the RR.  If a line begins with) s
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(a blank, then the owner is assumed to be the same as that of the) s
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(previous RR.  Blank lines are often included for readability.) s
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(Following the owner, we list the TTL, type, and class of the RR.  Class) s
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(and type use the mnemonics defined above, and TTL is an integer before) s
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(the type field.  In order to avoid ambiguity in parsing, type and class) s
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(mnemonics are disjoint, TTLs are integers, and the type mnemonic is) s
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(always last. The IN class and TTL values are often omitted from examples) s
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(in the interests of clarity.) s
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(The resource data or RDATA section of the RR are given using knowledge) s
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(of the typical representation for the data.) s
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(For example, we might show the RRs carried in a message as:) s
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(    ISI.EDU.        MX      10 VENERA.ISI.EDU.) s
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(                    MX      10 VAXA.ISI.EDU.) s
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(    VENERA.ISI.EDU. A       128.9.0.32) s
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(                    A       10.1.0.52) s
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(    VAXA.ISI.EDU.   A       10.2.0.27) s
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(                    A       128.9.0.33) s
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(The MX RRs have an RDATA section which consists of a 16 bit number) s
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(followed by a domain name.  The address RRs use a standard IP address) s
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(format to contain a 32 bit internet address.) s
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(This example shows six RRs, with two RRs at each of three domain names.) s
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(Similarly we might see:) s
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(    XX.LCS.MIT.EDU. IN      A       10.0.0.44) s
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(                    CH      A       MIT.EDU. 2420) s
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(This example shows two addresses for XX.LCS.MIT.EDU, each of a different) s
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(class.) s
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(3.6.2. Aliases and canonical names) s
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(In existing systems, hosts and other resources often have several names) s
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(that identify the same resource.  For example, the names C.ISI.EDU and) s
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(USC-ISIC.ARPA both identify the same host.  Similarly, in the case of) s
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(mailboxes, many organizations provide many names that actually go to the) s
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(same mailbox; for example [e-mail], [e-mail],) s
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(Mockapetris                                                    [Page 14]) s
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/fname (/usr/local/share/doc/rfc/Mirrors/ftp.isi.edu/in-notes/rfc1034.txt) def
/fdir (/usr/local/share/doc/rfc/Mirrors/ftp.isi.edu/in-notes/) def
/ftail (rfc1034.txt) def
% User defined strings:
/fmodstr (Tue Nov 24 00:00:00 1987) def
/pagenumstr (15) def
/user_header_p true def
/user_header_left_str (RFC1034) def
/user_header_center_str (RFC.net) def
/user_header_right_str (Page 15 of 56) def
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do_header
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(RFC 1034             Domain Concepts and Facilities        November 1987) s
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(and [e-mail] all go to the same mailbox \(although the mechanism) s
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(behind this is somewhat complicated\).) s
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(Most of these systems have a notion that one of the equivalent set of) s
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(names is the canonical or primary name and all others are aliases.) s
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(The domain system provides such a feature using the canonical name) s
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(\(CNAME\) RR.  A CNAME RR identifies its owner name as an alias, and) s
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(specifies the corresponding canonical name in the RDATA section of the) s
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(RR.  If a CNAME RR is present at a node, no other data should be) s
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(present; this ensures that the data for a canonical name and its aliases) s
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(cannot be different.  This rule also insures that a cached CNAME can be) s
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(used without checking with an authoritative server for other RR types.) s
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(CNAME RRs cause special action in DNS software.  When a name server) s
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(fails to find a desired RR in the resource set associated with the) s
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(domain name, it checks to see if the resource set consists of a CNAME) s
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(record with a matching class.  If so, the name server includes the CNAME) s
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(record in the response and restarts the query at the domain name) s
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(specified in the data field of the CNAME record.  The one exception to) s
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(this rule is that queries which match the CNAME type are not restarted.) s
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(For example, suppose a name server was processing a query with for USC-) s
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(ISIC.ARPA, asking for type A information, and had the following resource) s
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(records:) s
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(    USC-ISIC.ARPA   IN      CNAME   C.ISI.EDU) s
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(    C.ISI.EDU       IN      A       10.0.0.52) s
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(Both of these RRs would be returned in the response to the type A query,) s
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(while a type CNAME or * query should return just the CNAME.) s
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(Domain names in RRs which point at another name should always point at) s
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(the primary name and not the alias.  This avoids extra indirections in) s
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(accessing information.  For example, the address to name RR for the) s
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(above host should be:) s
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(    52.0.0.10.IN-ADDR.ARPA  IN      PTR     C.ISI.EDU) s
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(rather than pointing at USC-ISIC.ARPA.  Of course, by the robustness) s
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(principle, domain software should not fail when presented with CNAME) s
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(chains or loops; CNAME chains should be followed and CNAME loops) s
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(signalled as an error.) s
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(3.7. Queries) s
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(Queries are messages which may be sent to a name server to provoke a) s
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(Mockapetris                                                    [Page 15]) s
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/ftail (rfc1034.txt) def
% User defined strings:
/fmodstr (Tue Nov 24 00:00:00 1987) def
/pagenumstr (16) def
/user_header_p true def
/user_header_left_str (RFC1034) def
/user_header_center_str (RFC.net) def
/user_header_right_str (Page 16 of 56) def
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do_header
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(RFC 1034             Domain Concepts and Facilities        November 1987) s
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(response.  In the Internet, queries are carried in UDP datagrams or over) s
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(TCP connections.  The response by the name server either answers the) s
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(question posed in the query, refers the requester to another set of name) s
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(servers, or signals some error condition.) s
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(In general, the user does not generate queries directly, but instead) s
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(makes a request to a resolver which in turn sends one or more queries to) s
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(name servers and deals with the error conditions and referrals that may) s
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(result.  Of course, the possible questions which can be asked in a query) s
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(does shape the kind of service a resolver can provide.) s
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(DNS queries and responses are carried in a standard message format.  The) s
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(message format has a header containing a number of fixed fields which) s
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(are always present, and four sections which carry query parameters and) s
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(RRs.) s
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(The most important field in the header is a four bit field called an) s
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(opcode which separates different queries.  Of the possible 16 values,) s
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(one \(standard query\) is part of the official protocol, two \(inverse) s
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(query and status query\) are options, one \(completion\) is obsolete, and) s
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(the rest are unassigned.) s
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(The four sections are:) s
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(Question        Carries the query name and other query parameters.) s
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(Answer          Carries RRs which directly answer the query.) s
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(Authority       Carries RRs which describe other authoritative servers.) s
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(                May optionally carry the SOA RR for the authoritative) s
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(                data in the answer section.) s
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(Additional      Carries RRs which may be helpful in using the RRs in the) s
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(                other sections.) s
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(Note that the content, but not the format, of these sections varies with) s
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(header opcode.) s
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(3.7.1. Standard queries) s
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(A standard query specifies a target domain name \(QNAME\), query type) s
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(\(QTYPE\), and query class \(QCLASS\) and asks for RRs which match.  This) s
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(type of query makes up such a vast majority of DNS queries that we use) s
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(the term "query" to mean standard query unless otherwise specified.  The) s
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(QTYPE and QCLASS fields are each 16 bits long, and are a superset of) s
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(defined types and classes.) s
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(Mockapetris                                                    [Page 16]) s
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/pagenum 17 def
/fname (/usr/local/share/doc/rfc/Mirrors/ftp.isi.edu/in-notes/rfc1034.txt) def
/fdir (/usr/local/share/doc/rfc/Mirrors/ftp.isi.edu/in-notes/) def
/ftail (rfc1034.txt) def
% User defined strings:
/fmodstr (Tue Nov 24 00:00:00 1987) def
/pagenumstr (17) def
/user_header_p true def
/user_header_left_str (RFC1034) def
/user_header_center_str (RFC.net) def
/user_header_right_str (Page 17 of 56) de