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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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DNS: trailing periods

When I edit my bind dns records, I need to add a trailing period for it to work. What is the point of this? How come when I use everydns.net, they do not require me to add a trailing period? Is this an implementation quirk?
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What's the maximum number of IPs a DNS A record can have?

I have a strange idea - let multiple people/organizations host the same application, and let all their nodes be accessible via a single domain name. That's in order to have, let's say, a really distributed social network, where usability is not…
Bozho
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DNS - Multiple A records or 1 A record and lots of CNAMEs?

Lets say I have a webserver, called 'www'. www.example.com resolves to the IP address of that machine. Then I wanna make some virtual hosts, and DNS records for them, like webmail.example.com. For 'webmail', should I put in an A record with www's IP…
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Does Google Domains support CNAME-like functionality at the zone apex?

This functionality is required for properly directing a root domain to Heroku: https://devcenter.heroku.com/articles/custom-domains#cname-functionality-at-the-apex Some registrars, like DNSimple, support it. Is it supported by the new Google…
alpheus
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What does a DNS request look like?

I have seen what the text representation of an HTTP request is, but what does a DNS request look like? Where in the data is the location of the URL you are trying to locate? Also, how is the response formatted?
AMWJ
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How to test DNS glue record?

Hello I have just set up a DNS server for my domain example.org with 2 name servers ns1.example.org and ns2.example.org. I have attempted to set up a glue record for ns1 and ns2 at my registrar. It seems to work for now when I do a dig example.org…
Sunnz
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I changed my TTL from 24 hours to 5 minutes. Do I need to wait 24 hours before changing the records?

I am migrating our app from a cloud server at Rackspace t a dedicated server. I want to bring the application down for ~5 minutes to copy the data from the cloud server to the dedicated server, so I don't want requests going to the old server after…
wobbily_col
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Forward the root domain to the www subdomain using DNS records

I have www.mydomain.com pointed at an Azure Website. www.mydomain.com --- CNAME --- mydomain.azurewebsites.net When I visit www.mydomain.com, everything works fine. This is good. Problem is, mydomain.com doesn't work. Azure only allows the www…
Shaun Luttin
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DNS just started resolving my server.prod addresses to 127.0.53.53

I have servers named like server.prod.example.com, and I regularly log into them as server.prod. Recently, these hostnames started resolving to 127.0.53.53. It turns out that ICANN recently enabled the .prod TLD. In addition, every request that…
wfaulk
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Why does the host command not resolve entries in /etc/hosts?

I have the following /etc/hosts file on a ubuntu 12.04 machine 127.0.0.1 localhost 10.248.27.66 ec2-50-112-220-110.us-west-2.compute.amazonaws.com puppetmaster # The following lines are desirable for IPv6 capable hosts ::1 ip6-localhost…
user784637
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How do I redirect www to non-www in Route53?

I host my site at domain.com. My DNS entries in Route53 are as follows: domain.com A xxx.xxx.xxx.xxx 300 domain.com NS stuff.awsdns-47.org 172800 domain.com SOA stuff.awsdns-47.org 900 I would like to redirect…
fredley
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Configuring "@" CNAME record in GoDaddy control panel

I have mydomain.com that is hosted on an Azure VM instance called mymachine.cloudapp.net I need to configure DNS so that both www.mydomain.com and mydomain.com get mapped to the same host. I'm using GoDaddy as registrar. Currently GoDaddy offers me…
usr-local-ΕΨΗΕΛΩΝ
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How is DNS lookup configured for OSX Mountain Lion?

If I cat my resolv.conf, I see this message: # # Mac OS X Notice # # This file is not used by the host name and address resolution # or the DNS query routing mechanisms used by most processes on # this Mac OS X system. # # This file is automatically…
Ben Flynn
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Is there a way to use a specific DNS for a specific domain?

At work we use OpenDNS and it has wrongly blocked irc.freenode.net for malware. How can I make sure that any request for *.freenode.net goes to 8.8.8.8 and 8.8.4.4 (Google's DNS). I tried doing this by fiddling with resolv.conf on Ubuntu, but I…
vivin
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Do DNS queries always travel over UDP?

I've spent a bit of time researching this topic and can't seem to find an exact answer, so I'm fairly confident it's not a duplicate, and while my question is based on a security need, I think it's still safe to ask here but let me know if I need to…
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