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)

48
votes
2answers
18k views

What are SPF records, and how do I configure them?

This is a canonical question about setting up SPF records. I have an office with many computers that share a single external ip (I'm unsure if the address is static or dynamic). Each computer ...
140
votes
4answers
92k 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?
48
votes
8answers
52k 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 goes to ...
116
votes
3answers
58k views

Why can't a CNAME record be used at the apex (aka root) of a domain?

This is a Canonical Question about CNAMEs at the apices (or roots) of zones It's relatively common knowledge that CNAME records at the apex of a domain are a taboo practice. Example: example.com. IN ...
92
votes
21answers
43k views

Should we host our own nameservers?

This is a Canonical Question about whether to outsource DNS resolution for ones own domains I currently have my ISP providing DNS for my domain, but they impose limitations on adding records. ...
30
votes
2answers
2k views

Why is geo-redundant DNS necessary for small sites?

This is a Canonical Question about DNS geo-redundancy. It's extremely common knowledge that geo-redundant DNS servers located at separate physical locations are highly desirable when providing ...
172
votes
7answers
244k 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 ...
81
votes
2answers
137k views

How to configure a Windows machine to allow file sharing with a DNS alias

What process is necessary to configure a Windows environment 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 \\...
40
votes
4answers
5k 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. ...
60
votes
3answers
176k views

How does ServerName and ServerAlias work?

It's the following part of a virtual host config that I need further clarification on: <VirtualHost *:80> # Admin email, Server Name (domain name), and any aliases ServerAdmin example@...
20
votes
2answers
5k views

What is the role of NS records at the apex of a DNS domain?

$ORIGIN example.com. ; not necessary, using this to self-document $TTL 3600 @ IN SOA ns1.example.com. admin.example.com. ( 1970010100 7200 1800 1209600 300) @ ...
169
votes
16answers
147k 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 ...
16
votes
2answers
6k views

Website and Active Directory domain share the same name

In our network the name of the network domain is also the domain of the organization's website (say, example.com). Externally, people can enter example.com to visit our website, but internally, this ...
113
votes
7answers
98k views

Top level domain/domain suffix for private network?

At our office, we have a local area network with a purely internal DNS setup, on which clients all named as whatever.lan. I also have a VMware environment, and on the virtual-machine-only network, I ...
67
votes
1answer
61k 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 records ...
39
votes
3answers
75k views

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 ...
16
votes
1answer
11k views

In DNS can an IN NS point to a CNAME?

Is it allowed to have an NS record be a CNAME? E.g.: subdomain.example.com. IN NS ns1.example.com. ns1.example.com. CNAME foo.example.com. foo.example.com. IN A 10.1....
14
votes
5answers
16k views

Set root domain record to be a CNAME

I need to create an NS record for a domain that is a CNAME, for the purpose of having two domains pointed at one IP, and not having to maintain the current IP address in two different places. The DNS ...
38
votes
3answers
22k views

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 ...
25
votes
2answers
3k views

Do the SSH or FTP protocols tell the server to which domain I am trying to connect?

When using the ssh or ftp commands from the Bash shell, does the server that I am connecting to learn of the domain name used? I understand that the domain name is locally translated into an IP ...
5
votes
1answer
5k views

Set up BIND9 as DNS Firewall

With OpenDNS now needing one to be on the pro package to have filtering turned on, being on a tight budget, we are in need of free DNS filtering. After reading this link on how to block domains with ...
37
votes
8answers
64k views

Overriding some DNS entries in BIND for internal networks

I have an internal network with a DNS server running BIND, connected to the internet through a single gateway. My domain "example.com" is managed by an external DNS provider. Some of the entries in ...
45
votes
3answers
34k 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 ...
35
votes
3answers
40k views

Why multiple PTR records in DNS is not recommended?

I often read that using multiple PTR records in a DNS configuration is not recommended. However, the reasons are often vague, or not so obvious, naming: "it can cause problems", "can trigger bugs ...
78
votes
11answers
23k 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 ...
59
votes
10answers
71k 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 ...
84
votes
8answers
116k 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?
64
votes
18answers
61k 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 ...
65
votes
15answers
13k 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 system-...
64
votes
2answers
20k 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 ...
15
votes
5answers
182k views

Reverse DNS - how to correctly configure for SMTP delivery

I started a new service and we need to send emails to our customers (new account confirms, etc). My server is known as prod01.bidrodeo.com and resolves to 97.107.134.38 . For reverse DNS, 97.107....
13
votes
3answers
2k views

Apache: Scammers point dozens of domain names at my dedicated IP. How to prevent this?

For the sake of discussion, pretend that I have an Apache webserver which serves a website at www.example.org. This domain name resolves to the public IP address at 192.168.1.100 (pretend this is a ...
7
votes
3answers
8k views

What is the correct behaviour when Nameservers Change

I have been having some issues with a certain network supplier over unchanged nameservers making my site invisible to their customers. I wouldnt be bothered except that they are one of the largest ...
29
votes
3answers
17k views

Is dig +trace always accurate?

When the accuracy of a DNS cache is in question, dig +trace tends to be the recommended way of determining the authoritative answer for an internet facing DNS record. This seems to be particularly ...
22
votes
3answers
10k views

Naming a new Active Directory forest - why is split-horizon DNS not recommended?

Hopefully, we all know what the recommendations for naming an Active Directory forest are, and they're pretty simple. Namely, it can be summed up in a single sentence. Use a subdomain of an existing,...
11
votes
2answers
10k views

How browsers handle multiple IPs [closed]

Can someone direct me to information on exact browsers behavior when browser gets multiple A records for a given hostname (say ip1 and ip2), and one of them is not accessible. I interested in EXACT ...
18
votes
2answers
18k views

Why can't a domain's root be a CNAME? [duplicate]

I've just read this question which essentially says that when I set up DNS for example.com, the root record can't be a CNAME, it has to be an A record. My question is, why? I'm sure the clever ...
14
votes
5answers
41k views

My public website name and AD domain name are the same. How can I get to my external website from inside my network?

I am using my domain example.orgin my firm. I can use www.example.orgto view my website. If I try http://example.org from outsite my firm there is no problem, but if I try it from inside, my windows ...
25
votes
2answers
2k 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 ...
24
votes
5answers
25k 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 ...
66
votes
3answers
32k 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 ...
15
votes
13answers
27k views

Using .local for internal websites [duplicate]

Is it okay to use app.mycoolname.local for URLs that are private / internal? We have several applications that are web based, but they are private apps and are not exposed to the public. We have ...
6
votes
5answers
9k views

How can I automaticaly change the DNS A record to point my site to a secondary server in case of a failure?

My hosting is charging me a $50/month fee to put my servers on the same VLAN so that I create a cluster using the Network Load Balancing feature. I'm really not needing split the load between the ...
10
votes
4answers
1k views

How can I manage all of my domains with minimal configuration?

This is a Canonical Question about DNS server administration. I have one hundred or so domains. All of these domains need to be configured identically, but it seems like a huge waste of time to have ...
70
votes
22answers
11k 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: http://com./...
15
votes
8answers
8k views

Why is it called DNS “Propagation”?

I always hear system administrators talk about waiting for DNS records to propagate "around the Internet" or "around the world" when they talk about making DNS changes. The fact of the matter is that ...
23
votes
4answers
18k 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 ...
14
votes
3answers
25k views

How exactly should I set up DNS to delegate authority for subdomains?

I have servers hosted at a hosting provider and they also host the DNS records for my domain names. Now I want to add subdomains that are resolved by my own DNS service. So for example: the hosting ...
25
votes
1answer
4k views

Do internet standards require reverse DNS for every device?

The requirements surrounding reverse DNS are confusing! People frequently talk about everything breaking if reverse DNS is not present, and that sounds scary. Even in cases where applications don't ...
18
votes
3answers
13k views

How can I send visitors to the closest server using DNS?

Is there a way to localize dns entries? Meaning, that users from asia resolve mydomain.com to another ip than users from usa or europe. This would be helpful to give the users the server nearby. DNS ...