10-22-2015
Dns is just a lookup table. And yes, it can return multiple records for a query. It's supposed to provide a cheap man's round robin on the returns (but you never know how many things are doing lookups, so sort of random). You can run your own DNS server, point to it and lie (if you want) about being authoritative for "whatever" (e.g. unix.com). Then all clients can be tricked into seeing your mappings for unix.com if they use your "tricky" DNS. You could cache other non-housed requests.... so you DNS would be "complete", but doing a tricky override for "whatever" you wanted to lie about. Hopefully this scares you a bit and it's a good segue into DNSSEC, etc...
Do a query, pick the first answer. That's how it's normally done.
Queries for records you don't house start at the root (of all... the root servers... "dot" if you will), then goes to what we call the TLDs and so on. If you own a registered domain, you can associate a DNS to it to build the relationship required (if you do this without cooperation of the holder of the parent zone this won't work, the parent zone has to know how to delegate requests to your server... sometimes the parent zone will stand authoriatative for your zone by default and they'll handle servicing your records... but normallly, you'd tell them about your server and that it will now stand authoritative for those zone (your registered domain).
Oh... and there is some caching going on the speed this lookups up quite a bit.. but the root servers get hit pretty hard.
There are good books out there... I recommend you look at the documentation at:
https://www.isc.org/support/
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host(1) General Commands Manual host(1)
NAME
host - DNS lookup utility
SYNOPSIS
class] ndots] number] type] wait] name [server]
DESCRIPTION
is a simple utility for performing DNS lookups. It is normally used to convert names to IP addresses and vice versa. With no options or
operands, prints an annotated usage summary.
Options
Use only the IPv4 query transport.
Use only the IPv6 query transport.
Equivalent to using
Attempt to display the
records for zone name from all the listed authoritative name servers for that zone. The list of name servers is defined by the
records that are found for the zone.
Make a DNS query of class
class. This can be used to look up class resource records. The values for class are:
The Internet class (default).
The MIT Chaosnet class.
The MIT Athena Hesiod class.
The class values are case-insensitive.
Generate verbose output.
Now equivalent to the option. is provided for backwards compatibility. In previous versions, it switched on debugging traces.
Use the IP6.INT domain, as defined in RFC 1886,
to perform reverse lookups of IPv6 addresses. The default is to use IP6.ARPA.
Select list mode.
performs a zone transfer for zone name. Transfer the zone, printing out the and address records If is combined with all records
will be printed.
Set the number of dots that have to be in
name for it to be considered absolute. The default value is defined using the statement in or is if no statement is present.
Names with fewer dots are interpreted as relative names and will be searched for in the domains listed in the or directive in
Set the number of UDP retries for a lookup.
number indicates how many times will repeat a query that does not get answered. The default number of retries is 1. If number
is negative or zero, the number of retries is set to 1.
Make nonrecursive queries.
Setting this option clears the RD (recursion desired) bit in the query which makes. This should mean that the name server
receiving the query will not attempt to resolve the name operand.
This option enables to mimic the behavior of a name server by making nonrecursive queries and expecting to receive answers to
those queries that are usually referrals to other name servers.
Use a TCP connection when querying the name server.
TCP is automatically selected for queries that require it, such as zone transfer requests. By default uses UDP when making
queries.
Select the query type.
type can be any recognized query type: and so on. For potential values, see the command in nslookup(1) and the discussion in
named.conf(4).
The type values are case-insensitive.
When the option is omitted, automatically selects an appropriate query type. By default, it looks for records, but if the option
is given, queries are made for records. If the operand is an IPv4 or IPv6 address, queries for records.
For a query type of you can specify the starting serial number by appending an equals sign followed by the starting serial number
(for example,
Generate verbose output.
Set the time to wait for a reply to
wait seconds. If wait is less than 1, the wait interval is set to 1.
Effectively wait forever for a reply.
The time to wait for a response is set to the number of seconds given by the hardware's maximum value for an integer quantity.
Operands
name The domain name that is to be looked up. It can also be an IPv4 or IPv6 address, in which case will, by default, perform a
reverse lookup for that address.
server The name or IP address of the name server that should query. The default is the server or servers listed in
EXAMPLES
Using a host name:
Using an IP address:
AUTHOR
was developed by the Internet Systems Consortium (ISC).
FILES
SEE ALSO
dig(1), nslookup(1), named(1M), named.conf(4), resolver(4).
Requests for Comments (RFC): 1886, available online at
available online at
available from the Internet Systems Consortium at
BIND 9.3 host(1)