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Questions tagged [domain-name-system]

The Domain Name System, usually referred to by the acronym DNS, is a hierarchical, distributed database where the keys are domain names. Questions involving publicly accessible domains should include the real, Fully Qualified Domain Name (FQDN)

DNS is the Domain Name System, a hierarchical, distributed database where the keys are domain names.

The primary references are:

  • RFC 1034 - Domain Names - Concepts and Facilities
  • RFC 1035 - Domain Names - Implementation and Specification

These documents collectively form STD 13. RFC 2181 is a frequently cited reference for STD 13 that addresses some of the more confusing areas of operation.

The most common record types found in the DNS are:

  • "A" records - the mapping from a domain name to an IPv4 address
  • "AAAA" records - the mapping from a domain name to an IPv6 address
  • "MX" records - the mapping from a domain name to the host name of an SMTP server
  • "NS" records - used to delegate a portion of the hierarchy to specific DNS servers
  • "PTR" records - typically used (via in-addr.arpa.) to map an IPv4 address back to a domain name
  • "CNAME" records - used to alias a domain name to its canonical version

DNS packets are conventionally transported over UDP and TCP port 53. UDP is more commonly used, but larger DNS responses and zone transfers require TCP. See RFC 5966.

This Wikipedia article provides an approachable introduction to DNS.

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How to specify multiple included domains in SPF record?

Our business email is hosted on Google apps. In addition, our web server may also send email. Currently our SPF record in DNS looks like this: domain.com. IN TXT "v=spf1 a include:_spf.google.com -all" This is all fine, however now we've…
Aleks G
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Linux command line utility to resolve host names using /etc/hosts first

There are several command line utilities to resolve host names (host, dig, nslookup), however they all use nameservers exclusively, while applications in general look in /etc/hosts first (using gethostbyname I believe). Is there a command line…
Zulan
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Windows 7: "localhost name resolution is handled within DNS itself". Why?

After 18 years of hosts files on Windows, I was surprised to see this in Windows 7 build 7100: # localhost name resolution is handled within DNS itself. # 127.0.0.1 localhost # ::1 localhost Does anyone know why this change was introduced? I'm…
Portman
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When do DNS queries use TCP instead of UDP?

Possible Duplicate: Is it true that a nameserver have to answer queries over TCP? I know DNS uses UDP for most of its queries, but in what circumstances will it use TCP instead?
pradeepchhetri
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What does the "IN" mean in a zone file?

Sometimes a record is listed as www IN A 192.168.1.1 and sometimes it is listed as www A 192.168.1.1. What is the purpose of the IN and when is it required/not required?
Tabitha
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Why should I use Amazon Route 53 over my registrar's DNS servers?

I am building a site that I anticipate will have high usage. Currently, my registrar (GoDaddy) is handling DNS. However, Amazon's Route 53 looks interesting. They promise high speed and offer globally distributed DNS servers and a programmable…
Abtin Forouzandeh
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How can I find the LDAP server in the DNS on Windows?

For Linux, this command should return the DNS record for the LDAP server host -t srv _ldap._tcp.DOMAINNAME (found at Authenticating from Java (Linux) to Active Directory using LDAP WITHOUT servername) How could I get the same on the Windows command…
mjn
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Can a CNAME DNS record point to a subdirectory

Can a DNS record point to an address like my.domain.com/subdir1
Hannes de Jager
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Can someone using the same DNS server as me hijack my domains?

When I register a new domain, I send it to my hosting provider by assigning it its domain name servers in the registar's settings. For example, with Digital Ocean, I input the…
Eran Galperin
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Is there a maximum subdomain depth?

Is there a maximum allowed subdomain depth supported by webservers or browsers? For example, could a domain like foo.bar.baz.monkey.pirate.google.com cause problems?
braveterry
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Recommended DNS SOA record TTL default?

We currently have our DNS SOA record set to the following for stackoverflow.com: primary name server = ns1.p19.dynect.net serial = 2009090909 refresh = 3600 (1 hour) retry = 600 (10 mins) expire = 604800 (7 days) default…
Geoff Dalgas
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How to disable AAAA lookups?

... to compensate for broken DNS servers that are outside our control. Our problem: We deploy embedded devices that collect sensor data at various, mostly IPv4-only sites. Some sites have poorly maintained networks, e.g. misconfigured or otherwise…
Nils Toedtmann
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CNAME for top of domain?

Is it possible to set a CNAME record at the top of a domain? (i.e. @ CNAME www, @ CNAME foobar.com., etc.) My ISP says that it's only possible to use CNAME's for subdomains but I've read somewhere else that is should be possible even if not…
Martin
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How to list all CNAME records for a given domain?

I cannot list them using dig/nslookup/host.
Paweł Gościcki
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What should the order of DNS servers be for an AD Domain Controller and Why?

This is a Canonical Question about Active Directory DNS Settings. Related: What is Active Directory Domain Services and how does it work? Assuming an environment with multiple domain controllers (assume that they all run DNS as well): in what…
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