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

learn more… | top users | synonyms

107
votes
15answers
88k views

Why is DNS failover not recommended?

From reading, it seems like DNS failover is not recommended just because DNS wasn't designed for it. But if you have two webservers on different subnets hosting redundant content, what other methods ...
73
votes
10answers
218k views

What's the command-line utility in Windows to do a reverse DNS look-up?

Is there a built-in command line tool that will do reverse DNS look-ups in Windows? I.e., something like <toolname> w.x.y.z => mycomputername I've tried: nslookup: seems to be forward ...
72
votes
6answers
66k views

Setting the hostname: FQDN or short name?

I've noticed that the "preferred" method of setting the system hostname is fundamentally different between Red Hat/CentOS and Debian/Ubuntu systems. CentOS documentation and the RHEL deployment guide ...
59
votes
2answers
82k views

How to Configure Windows Machine to Allow File Sharing with DNS Alias

What process is necessary to configure a Windows environement to allow me to use DNS CNAME to reference servers? I want to do this so that I can name my servers something like SRV001, but still have ...
57
votes
7answers
5k views

DNS failing to propagate worldwide

I haven't changed anything related to the DNS entry for serverfault.com, but some users were reporting today that the serverfault.com DNS fails to resolve for them. I ran a justping query and I can ...
56
votes
14answers
33k views

Top level domain for private networks?

On our office network we have an internal DNS and all the hostnames are whatever.lan. On my VMware VMs, on their host-only network I call them whatever.vm. We now have a private IP space network in ...
55
votes
22answers
9k views

How the heck is http://to./ a valid domain name?

Apparently it's a URL shortener. It resolves just fine in Chrome and Firefox. How is this a valid top-level domain? Update: for the people saying it's browser shenanigans, why is it that: ...
53
votes
20answers
21k views

Should we host our own nameservers?

I currently have my ISP providing DNS for my domain, but they impose limitations on adding records. Therefore, I am thinking about running my own DNS. Do you prefer to host your own DNS, or is it ...
53
votes
11answers
14k views

Multiple data centers and HTTP traffic: DNS Round Robin is the ONLY way to assure instant fail-over?

Multiple A records pointing to the same domain seem to be used almost exclusively to implement DNS Round Robin as a cheap load balancing technique. The usual warning against DNS RR is that it is not ...
50
votes
15answers
8k views

Are IP addresses “trivial to forge”?

I was reading through some of the notes on Google's new public DNS service: Performance Benefits Security Benefits I noticed under the security section this paragraph: Until a standard ...
48
votes
3answers
18k views

What is a glue record?

This is a Canonical Question about DNS glue records. What exactly (but briefly) is a DNS glue record? Why are they needed and how do they work?
47
votes
8answers
45k views

Is a wildcard CNAME DNS record valid?

I know it's valid to have a DNS A record that's a wildcard (e.g. *.mysite.com). Is it possible/valid/advised to have a wildcard CNAME record?
45
votes
6answers
83k views

List all DNS records in a domain using dig?

My company runs an internal DNS for "mycompany.com" There is a machine on the network that I need to find, but I've forgotten it's name. If I could see a list, it would probably jog my memory. ...
39
votes
4answers
53k views

How can I see Time-to-live (TTL) for a DNS record?

I would like to see the Time-to-live (TTL) value for a CNAME record. I have access to dig (on Apple Leopard), which gives me an answer like this: % dig host.example.gov <*SNIP*> ;; ANSWER ...
39
votes
1answer
36k views

How long does it take for DNS records to propagate?

This is a Canonical Question about DNS Propagation How long does it take for an the various types of records to propagate? Do some propagate faster than others? Why does it take time for DNS ...
33
votes
4answers
2k views

Why does DNS work the way it does?

This is a Canonical Question about DNS (Domain Name Service). If my understanding of the DNS system is correct, the .com registry holds a table that maps domains (www.example.com) to DNS servers. ...
33
votes
5answers
2k views

Phishing site uses subdomain that I never registered

I recently received the following message from Google Webmaster Tools: Dear site owner or webmaster of http://gotgenes.com/, [...] Below are one or more example URLs on your site which ...
33
votes
23answers
5k views

Who is a good registrar these days? [closed]

It's been a long time since I've had to register a new domain. What registrar is considered geek and sysadmin friendly? I've heard that godaddy will screw you 10 ways to Sunday, and a lot of the ...
33
votes
6answers
45k views

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 ...
32
votes
16answers
30k views

Is Round-Robin DNS “good enough” for load balancing static content?

We have a set of shared, static content that we serve up between our websites at http://sstatic.net. Unfortunately, this content is not currently load balanced at all -- it's served from a single ...
32
votes
10answers
4k views

Run antivirus software on linux DNS servers. Does it make sense?

During a recent audit we were requested to install antivirus software on our DNS servers that are running linux (bind9). The servers were not compromised during the penetration testing but this was ...
31
votes
2answers
7k views

Why does Heroku warn against “naked” domain names?

I ran across this page in the Heroku docs... Naked domains, also called bare or apex domains, are configured in DNS via A-records and have serious availability implications when used in highly ...
30
votes
9answers
2k views

What's the piece of hardware listening on Facebook's or Wikipedia's IP address?

I am trying to understand how massive sites like Facebook or Wikipedia work, for my intellectual curiosity. I read about various techniques for building scalable sites, but I am still puzzled about ...
29
votes
2answers
13k views

Should CNAME Be Used For Subdomains?

I manage multiple websites that currently have the following DNS configuration: example.com - A Record - Production Server IP test.example.com - A Record - Test Server IP www.example.com - ...
28
votes
10answers
19k views

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 ...
27
votes
3answers
12k views

What's the meaning of '@' in a DNS zone file?

I have the following data in my dns file, for my domain... $ORIGIN mydomain.com. @ IN A 208.X.Y.Z mail IN A 208.X.Y.Z ... etc.. what is the @ line, mean? I know what ...
26
votes
8answers
22k views

Private IP address in public DNS

We have an SMTP only mail server behind a firewall which will have a public A record of mail.. The only way to access this mail server is from another server behind the same firewall. We do not run ...
26
votes
1answer
11k views

EC2: is an instance's public DNS stable? Can I rely on it not changing?

I'm new to Amazon EC2. I've launched my first instance, and am using it as a web server. I see that it has a public DNS (a public URL), e.g.: ec2-123-45-6-789.compute-1.amazonaws.com I can ...
25
votes
2answers
9k views

Vagrant / virtualbox DNS 10.0.2.3 not working

This is a follow on to my previous question Vagrant Getting Started gives getaddrinfo: Temporary failure in name resolution. I am running a fresh install of Linux Mint Nadia (14). I am following the ...
25
votes
2answers
2k views

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?
25
votes
2answers
55k views

DNS - NSLOOKUP what is the meaning of the non-authorative answer?

When I do a NS Lookup, for some domains I get the reply saying Non-authorative answer:. I want to know what it means? Got answer: HEADER: opcode = QUERY, id = 3, rcode = NXDOMAIN ...
25
votes
3answers
36k views

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 ...
25
votes
14answers
3k views

Load-balancer options [closed]

I am looking at a number of possible options for load-balancing. So far, I am constrained to the following options: DNS server load-balancer, balancing to a cluster of tomcat servers, with ...
24
votes
5answers
15k views

Geo-DNS providers? [closed]

We've got a website visited by users mainly in the USA and UK. The site will be run on servers in both these locations. We would like to use a DNS service to direct users to the nearest server, but ...
23
votes
8answers
2k views

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 ...
22
votes
5answers
7k views

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 ...
21
votes
6answers
10k views

Is it possible for two hostnames share the same IP address?

Can anyone explain whether it is possible for two hostnames to share the same IP address? And what about if one hostname represents more than one IP address, is that possible too? Why?
21
votes
5answers
4k views

A domain I've never heard of resolves to my website [duplicate]

I've discovered (via looking at mod_pagespeed cache entries) that a completely random domain I've never heard of before is resolving to my website. If I visit this domain, my website loads. The DNS ...
21
votes
3answers
3k views

Problems with DNS propagation 10 days after a change was made

The engineering team I work with has been in the process of moving equipment from one datacenter to another. Ten days ago we moved one of our name servers authoritative for our client's domains ...
20
votes
5answers
23k views

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 ...
20
votes
4answers
21k views

How to include multiple domains in an spf TXT Record

I am looking to setup a TXT spf record that has 2 included domains... individually: v=spf1 include:_spf.google.com ~all and v=spf1 include:otherdomain.com ~all What is the proper way of ...
20
votes
3answers
7k views

is a CNAME to CNAME chain allowed

Is it allowed in DNS to have a CNAME record that points to another CNAME record? The reason we need this is that we have a hostname that we want to be looked up to the IP address of our web server ...
19
votes
11answers
6k views

djbdns vs bind [closed]

I'm a newbie who wants to learn how to set up a DNS nameserver. Should I use djbdns, BIND, or something else? Current network requirements include subdomain support, SSL, and mail service, all on ...
19
votes
1answer
704 views

How do I set up a “secure” open resolver?

This is a Canonical Question about securing public DNS resolvers Open DNS servers seem pretty neat and convenient, as they provide IP addresses that we can use consistently across our company ...
19
votes
1answer
310 views

When I have a * entry in my zone file, how can I treat a specific name as nonexistent?

On our main domain, example.com we're hosting a lot of websites. So we just added a * A/AAAA record to our zone and pointed it at our webserver. Sadly, this also causes Outlook to constantly hammer ...
18
votes
7answers
13k views

How to use DNS/Hostnames or Other ways to resolve to a specific IP:Port

This is a Canonical Question about DNS/Hostnames resolution to IPs/Ports Example 1 I'm running a web server on port 80 and another on port 87. I would like to use DNS so that www.example.com ...
18
votes
3answers
10k views

Linux command to inspect TXT records of a domain

Is there a linux shell command that I can use to inspect the TXT records of a domain?
18
votes
4answers
10k views

Reverse DNS in a CIDR world

Reverse DNS seems to be strongly tied to class boundaries, what methods exist now that CIDR is the standard to delegate authority for a subnet? If multiple methods exist which one is best? Do you ...
18
votes
7answers
37k views

Can you lookup a domains past nameserver & mx record history?

If is possible to find out which nameservers a domain was previously pointing too? I need to try and find where a domain was previously hosted so that I can try and gain access to an old hosted email ...
18
votes
6answers
781 views

Why do Facebook users sometimes end up on my site when they enter www.facebook.com in their browser?

Every few weeks I get an email (usually a very unpleasant one) or sometimes even a phone call from a Facebook user who believes that I am "hacking" their internet. They come to this conclusion after ...