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Full Discussion: DNS and hostname resolution
Special Forums IP Networking DNS and hostname resolution Post 302958488 by cjcox on Thursday 22nd of October 2015 03:29:19 PM
Old 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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unbound(8)							   unbound 1.5.1							unbound(8)

NAME
unbound - Unbound DNS validating resolver 1.5.1. SYNOPSIS
unbound [-h] [-d] [-v] [-c cfgfile] DESCRIPTION
Unbound is a caching DNS resolver. It uses a built in list of authoritative nameservers for the root zone (.), the so called root hints. On receiving a DNS query it will ask the root nameservers for an answer and will in almost all cases receive a delegation to a top level domain (TLD) authoritative nameserver. It will then ask that nameserver for an answer. It will recursively continue until an answer is found or no answer is available (NXDO- MAIN). For performance and efficiency reasons that answer is cached for a certain time (the answer's time-to-live or TTL). A second query for the same name will then be answered from the cache. Unbound can also do DNSSEC validation. To use a locally running Unbound for resolving put nameserver 127.0.0.1 into resolv.conf(5). If authoritative DNS is needed as well using nsd(8), careful setup is required because authoritative nameservers and resolvers are using the same port number (53). The available options are: -h Show the version and commandline option help. -c cfgfile Set the config file with settings for unbound to read instead of reading the file at the default location, /var/unbound/unbound.conf. The syntax is described in unbound.conf(5). -d Debug flag: do not fork into the background, but stay attached to the console. This flag will also delay writing to the log file until the thread-spawn time, so that most config and setup errors appear on stderr. If given twice or more, logging does not switch to the log file or to syslog, but the log messages are printed to stderr all the time. -v Increase verbosity. If given multiple times, more information is logged. This is in addition to the verbosity (if any) from the config file. SEE ALSO
unbound.conf(5), unbound-checkconf(8), nsd(8). AUTHORS
Unbound developers are mentioned in the CREDITS file in the distribution. NLnet Labs Dec 8, 2014 unbound(8)
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