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DNS

Stability: 3 - Stable

Use require('dns') to access this module. All methods in the dns module use C-Ares except for dns.lookup which uses getaddrinfo(3) in a thread pool. C-Ares is much faster than getaddrinfo(3) but, due to the way it is configured by node, it doesn't use the same set of system configuration files. For instance, C- Ares will not use the configuration from /etc/hosts. As a result, only dns.lookup should be expected to behave like other programs running on the same system regarding name resolution. When a user does net.connect(80, 'google.com') or http.get({ host: 'google.com' }) the dns.lookup method is used. Users who need to do a large number of lookups quickly should use the methods that go through C-Ares.

Here is an example which resolves 'www.google.com' then reverse resolves the IP addresses which are returned.

var dns = require('dns');

dns.resolve4('www.google.com', function (err, addresses) {
  if (err) throw err;

  console.log('addresses: ' + JSON.stringify(addresses));

  addresses.forEach(function (a) {
    dns.reverse(a, function (err, domains) {
      if (err) {
        throw err;
      }

      console.log('reverse for ' + a + ': ' + JSON.stringify(domains));
    });
  });
});

dns.lookup(domain, [family], callback)

Resolves a domain (e.g. 'google.com') into the first found A (IPv4) or AAAA (IPv6) record. The family can be the integer 4 or 6. Defaults to null that indicates both Ip v4 and v6 address family.

The callback has arguments (err, address, family). The address argument is a string representation of a IP v4 or v6 address. The family argument is either the integer 4 or 6 and denotes the family of address (not necessarily the value initially passed to lookup).

On error, err is an Error object, where err.code is the error code. Keep in mind that err.code will be set to 'ENOENT' not only when the domain does not exist but also when the lookup fails in other ways such as no available file descriptors.

dns.resolve(domain, [rrtype], callback)

Resolves a domain (e.g. 'google.com') into an array of the record types specified by rrtype. Valid rrtypes are 'A' (IPV4 addresses, default), 'AAAA' (IPV6 addresses), 'MX' (mail exchange records), 'TXT' (text records), 'SRV' (SRV records), 'PTR' (used for reverse IP lookups), 'NS' (name server records) and 'CNAME' (canonical name records).

The callback has arguments (err, addresses). The type of each item in addresses is determined by the record type, and described in the documentation for the corresponding lookup methods below.

On error, err is an Error object, where err.code is one of the error codes listed below.

dns.resolve4(domain, callback)

The same as dns.resolve(), but only for IPv4 queries (A records). addresses is an array of IPv4 addresses (e.g. ['74.125.79.104', '74.125.79.105', '74.125.79.106']).

dns.resolve6(domain, callback)

The same as dns.resolve4() except for IPv6 queries (an AAAA query).

dns.resolveMx(domain, callback)

The same as dns.resolve(), but only for mail exchange queries (MX records).

addresses is an array of MX records, each with a priority and an exchange attribute (e.g. [{'priority': 10, 'exchange': 'mx.example.com'},...]).

dns.resolveTxt(domain, callback)

The same as dns.resolve(), but only for text queries (TXT records). addresses is an array of the text records available for domain (e.g., ['v=spf1 ip4:0.0.0.0 ~all']).

dns.resolveSrv(domain, callback)

The same as dns.resolve(), but only for service records (SRV records). addresses is an array of the SRV records available for domain. Properties of SRV records are priority, weight, port, and name (e.g., [{'priority': 10, {'weight': 5, 'port': 21223, 'name': 'service.example.com'}, ...]).

dns.resolveNs(domain, callback)

The same as dns.resolve(), but only for name server records (NS records). addresses is an array of the name server records available for domain (e.g., ['ns1.example.com', 'ns2.example.com']).

dns.resolveCname(domain, callback)

The same as dns.resolve(), but only for canonical name records (CNAME records). addresses is an array of the canonical name records available for domain (e.g., ['bar.example.com']).

dns.reverse(ip, callback)

Reverse resolves an ip address to an array of domain names.

The callback has arguments (err, domains).