| Rev | Author | # | Line |
|---|---|---|---|
| 9 | AristotlePagaltzis | 1 | The smallest unit of queriable data in the [DNS]. Each ResourceRecord has a type which gives particular meaning to its payload. These types include: |
| 4 | MikeBeattie | 2 | |
| 9 | AristotlePagaltzis | 3 | __<tt>A</tt>__: |
| 4 | Short for "address". An [IPv4] address. Specified in RFC:1035. Example: | ||
| 5 | <verbatim> | ||
| 6 | foo.example.org A 1.2.3.4 | ||
| 7 | </verbatim> | ||
| 4 | MikeBeattie | 8 | |
| 9 | AristotlePagaltzis | 9 | __<tt>AAAA</tt>__: |
| 10 | Like <tt>A</tt>, but stores an [IPv6] address; to be obsoleted by <tt>A6</tt>. Specified in RFC:1886. Example: | ||
| 11 | <verbatim> | ||
| 12 | foo.example.org AAAA 2002:c000:0200::1 | ||
| 13 | </verbatim> | ||
| 4 | MikeBeattie | 14 | |
| 9 | AristotlePagaltzis | 15 | __<tt>A6</tt>__: |
| 16 | Supposed to obsolete <tt>AAAA</tt> for [IPv6] addresses. | ||
| 17 | Many people continue using <tt>AAAA</tt> due to the complexity of A6, see [AAAAvsA6]. | ||
| 18 | Specified in RFC:2874. Example: | ||
| 19 | <verbatim> | ||
| 20 | $ORIGIN X.EXAMPLE. | ||
| 21 | N A6 64 ::1234:5678:9ABC:DEF0 SN-1.IP6 | ||
| 22 | SN-1.IP6 A6 48 0:0:0:1:: IP6 | ||
| 23 | IP6 A6 48 0::0 CUST-X.IP6.A.NET. | ||
| 24 | IP6 A6 48 0::0 CUST-X.IP6.B.NET. | ||
| 25 | </verbatim> | ||
| 4 | MikeBeattie | 26 | |
| 9 | AristotlePagaltzis | 27 | __<tt>CNAME</tt>__: |
| 28 | Short for Canonical Name, an alias for a hostname. | ||
| 29 | Often used for well known services so that <tt>www.example.com</tt> points to <tt>arthur.example.com</tt>. | ||
| 30 | Specified in RFC:1035. Example: | ||
| 31 | <verbatim> | ||
| 32 | www.xtra.co.nz CNAME xtra.co.nz | ||
| 33 | xtra.co.nz A 202.27.184.102 | ||
| 34 | |||
| 35 | mail.xtra.co.nz CNAME mta.xtra.co.nz | ||
| 36 | mta.xtra.co.nz A 203.96.92.132 | ||
| 37 | </verbatim> | ||
| 38 | Some record types in [DNS] are not allowed to be <tt>CNAME</tt>s. Similar to <tt>DNAME</tt>. See the NamedNotes page for more details. | ||
| 39 | |||
| 40 | __<tt>DNAME</tt>__: | ||
| 41 | Basically a <tt>CNAME</tt> for an entire domain. Specified in RFC:2672. Example: | ||
| 42 | <verbatim> | ||
| 43 | test.meta.net.nz. IN DNAME wlug.org.nz. | ||
| 44 | </verbatim> | ||
| 45 | With this in place <tt>[www.test.meta.net.nz|http://www.test.meta.net.nz/]</tt> resolves to <tt>www.wlug.org.nz</tt>. | ||
| 46 | |||
| 47 | Support for this feature is spotty. DanBernstein refuses to implement it and it doesn't seem to be mentioned at all in MicrosoftWindows (as of 2004-07-14). | ||
| 48 | Only [BIND] seems to support it, but since it will also serve you a <tt>CNAME</tt>, most resolvers should deal with it properly: | ||
| 49 | <verbatim> | ||
| 50 | test.meta.net.nz. 86400 IN DNAME wlug.org.nz. | ||
| 51 | www.test.meta.net.nz. 0 IN CNAME www.wlug.org.nz. | ||
| 52 | www.wlug.org.nz. 80464 IN CNAME hoiho.wlug.org.nz. | ||
| 53 | hoiho.wlug.org.nz. 80464 IN A 203.97.10.50 | ||
| 54 | </verbatim> | ||
| 55 | MicrosoftWindows still seems to get confused however. | ||
| 56 | |||
| 57 | __<tt>LOC</tt>__: | ||
| 58 | [GPS] location of the machine or site. Specified in RFC:1876. Example: | ||
| 59 | <verbatim> | ||
| 60 | waikato.ac.nz. LOC 37 48 30.000 S 175 17 36.000 E 66.00m 3000m 30m 10m | ||
| 61 | </verbatim> | ||
| 62 | This means 37 deg 48' 30" South (latitude), 175 deg 17' 36" East (longitude), and 66 metres about sea level. | ||
| 63 | The last two numbers appear to mean that the whole site is within 3000 metres of the given point. | ||
| 64 | The point is accurate to about 30 metres, although this interpretation may be wrong. | ||
| 65 | (It will be in the appropriate [RFC] if anyone can be bothered looking it up.) | ||
| 66 | |||
| 67 | xtraceroute(1) will use these records if it can find them. Unfortunately not many sites use them. | ||
| 68 | |||
| 69 | __<tt>MX</tt>__: | ||
| 70 | MailExchanger. Identifies the [SMTP] MailServer(s) responsible for the domain. | ||
| 71 | When no <tt>MX</tt> record exists and an <tt>A</tt> record does, the <tt>A</tt> record is chosen to take mail. | ||
| 72 | Specified in RFC:1035. Example: | ||
| 73 | <verbatim> | ||
| 74 | foo.com. IN MX 10 mail.foo.com. | ||
| 75 | </verbatim> | ||
| 76 | The "10" is the priority. Delivery will be attempted to MailServer~s in order of ascending priority value. | ||
| 77 | |||
| 78 | __Note:__ the data for an <tt>MX</tt> record is a host name, __NOT__ an [IP] address. The following will __NOT__ work: | ||
| 79 | <verbatim> | ||
| 80 | foo.com. IN MX 10 130.123.7.10 | ||
| 81 | </verbatim> | ||
| 82 | |||
| 83 | Also, the host name (<tt>mail.foo.com</tt> in the example) __MUST__ have an <tt>A</tt> record, __NOT__ a <tt>CNAME</tt> record. | ||
| 84 | |||
| 85 | __<tt>NS</tt>__: | ||
| 12 | LawrenceDoliveiro | 86 | In the initial part of a ZoneFile, indicates the NameServer~s which are [authoritative|AuthoritativeNameServer] for this domain. Elsewhere, indicates that a [subdomain|DomainName] is being [delegated|Delegation] to another set of NameServer~s. Specified in RFC:1035. |
| 9 | AristotlePagaltzis | 87 | |
| 88 | __<tt>PTR</tt>__: | ||
| 89 | A pointer. Used for a ReverseLookup. Specified in RFC:1035. Example: | ||
| 90 | <verbatim> | ||
| 91 | 192 PTR hostname.domain. | ||
| 92 | </verbatim> | ||
| 93 | __Note:__ don't forget the trailing fullstop! | ||
| 94 | |||
| 95 | __<tt>SOA</tt>__: | ||
| 96 | Start of Authority. Defines information about a domain (called a zone, defined in a ZoneFile), such as a serial number defining the 'version' of the zone, and various timeout and caching values that should be used when records from a given zone are retrieved. The format <tt>name <ttl> class rr name-server email-address (serial refresh retry expire negttl)</tt>. Specified in RFC:1035. Example: | ||
| 97 | <verbatim> | ||
| 98 | $TTL 604800 | ||
| 99 | $ORIGIN ethernal.tla. | ||
| 100 | @ IN SOA ns1.ethernal.tla. root.ethernal.tla. ( | ||
| 101 | 2004111901 ; Serial | ||
| 102 | 604800 ; Refresh (7 days) | ||
| 103 | 86400 ; Retry (24 hours) | ||
| 104 | 2419200 ; Expire (28 days) | ||
| 105 | 604800 ) ; Neg TTL (7 days) | ||
| 106 | </verbatim> | ||
| 107 | The name is given as "<tt>@</tt>", since that is the shorthand for the value of <tt>$ORIGIN</tt>. [TTL] is missing from this example, as it takes the zone default defined above as <tt>$TTL</tt>. The name-server field is basically the [FQDN] of the PrimaryNameServer for the domain (don't forget the trailing fullstop!). The email-address field is the address of the person responsible for the domain -- the first dot should be read as an <tt>@</tt>, so above should be read as <tt>root@ethernal.tla</tt>. The values in parenthesis are described below: | ||
| 108 | |||
| 109 | Serial number:: | ||
| 13 | LawrenceDoliveiro | 110 | Generally given in YYYYMMDDXX format, giving 100 possible revisions of any given zone in a day (Usually more than enough). __Always remember to increment this when editing the ZoneFile__, since a change to the serial number is what triggers ZoneTransfer~s by SecondaryNameServer~s. |
| 9 | AristotlePagaltzis | 111 | Refresh:: |
| 13 | LawrenceDoliveiro | 112 | Defines the interval in seconds between checks by a SecondaryNameServer as to whether the serial number has changed. When a change is detected, this means it needs to refresh its copy of the zone by requesting a ZoneTransfer from the PrimaryNameServer. |
| 9 | AristotlePagaltzis | 113 | Retry:: |
| 114 | Defines the number of seconds for a SecondaryNameServer to wait before retrying a zone refresh, after a failure. | ||
| 115 | Expire:: | ||
| 116 | Defines the number of seconds for a SecondaryNameServer to keep zone records, and answer authoritatively with them if it can't contact the PrimaryNameServer. (so, if the above refresh fails, and it's been retrying for this long). | ||
| 117 | Neg TTL:: | ||
| 118 | Defines the number of seconds that a client should remember that a negative response was received from this server. So, if a remote server asks us what the address for <tt>foo.ethernal.tla</tt> is but it doesn't exist, it will cache the negative answer we gave it for this many seconds, even if we add that name to the zone a couple of seconds later. | ||
| 14 | LawrenceDoliveiro | 119 | |
| 120 | __<tt>[SRV]</tt>__ | ||
| 9 | AristotlePagaltzis | 121 | |
| 122 | __<tt>TXT</tt>__: | ||
| 123 | Up to 255 bytes of arbitrary binary data. Specified in RFC:1035. | ||
| 124 | |||
| 125 | A more comprehensive list of ResourceRecord~s is at: http://www.dns.net/dnsrd/rr.html | ||
| 4 | MikeBeattie | 126 | |
| 127 | ---- | ||
| 128 | CategoryDns |
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