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

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How is it possible for the Root Name Servers to handle all DNS requests?

I was reading about DNS some days ago and learned how the requests are processed. If you surf to www.example.com, then a request will go to the Root Name Servers to see who owns that .com address, ...
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4answers
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Will adding a second SPF record mess up my DNS?

Will adding a second SPF record mess up my DNS, or will it be like adding an extra nameserver? (i.e. it only helps, not hurts)
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3answers
729 views

Basic DNS - Forwarders vs. Root Hints

New here, but I have learned a great deal by looking around. My question is probably a simple one: In Microsoft Active Directory, does DNS look at the forwarders before it goes to the root hints? ...
13
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4answers
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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 ...
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9answers
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Public Facing Recursive DNS Servers - iptables rules

We run public-facing recursive DNS servers on Linux machines. We've been used for DNS amplification attacks. Are there any recommended iptables rules that would help mitigate these attacks? The ...
13
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2answers
849 views

Are subdomains public information?

Assuming you wanted to create a subdomain that points to a private location (perhaps the location of a database, or the IP address of a computer you don't want people to attempt SSH-ing into), so you ...
13
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1answer
12k views

How is DNS related to Active Directory and what are some common configurations that I should be aware of?

Please note that I do know the answer to this and have provided one below. I see a lot of newer systems administrators that don't understand the contents of my answer, so I hope that all of the ...
13
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1answer
2k 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 ...
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12answers
3k views

Will SRV records ever become usefull?

In DNS an SRV record really is a pretty generic form of telling a remote client where a specific service is hosted. At this moment I use it for allowing people to call me using a SIP client over the ...
12
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1answer
607 views

How can e-mail be delivered to a domain without an MX record?

Somebody has 2 e-mail addresses: bob@domainname.com.br and bob@domainname.com . The DNS records for these domains look like this: domainname.com.br $ dig any domainname.com.br ;; ANSWER SECTION: ...
12
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2answers
4k 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 ...
12
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3answers
5k 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?
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2answers
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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 ...
12
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3answers
4k 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 ...
12
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3answers
18k views

Do entries in local 'hosts' files override both forward and reverse name lookups?

If I have the following entries in a hosts file: 192.168.100.1 bugs 192.168.100.2 daffy.example.com 192.168.100.3 elmer.example.com. Will IP->name resolution attempts by local utilies (I ...
12
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2answers
757 views

Should engineering have its own DNS zone, delegate, or subdomain?

We have our organization's primary domain (with AD) example.com. In the past, previous admins have created several other zones - such as dmn.com, lab.example.com, dmn-geo.com etc - as well as ...
12
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3answers
643 views

DNS down in Anonymous attack

As I'm writing this our company website and the web-service we developed are down in the big GoDaddy outage resulting from an Anonymous attack (or so says Twitter). We used GoDaddy as our registrar ...
12
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2answers
2k views

Who actually “recurses” in a recursive DNS lookup?

I'm trying to understand the difference between iterative and recursive DNS lookups. Fundamentally, I think of iterative as being like calling a department store looking for a product, and when they ...
12
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4answers
2k views

Changing DNS serial number to be in the past

I have some DNS servers for our organization that was setup by my predecessor. He did not use the standard format for serial numbers, instead he used an odd format starting with 2033. What I want to ...
12
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3answers
3k views

What percentage of nameservers honor TTL these days?

Some years ago I had to do several DNS changes over the course of several weeks as I moved bits of equipment from one data center to the other. At the time that I did this, about 95% of the ...
12
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3answers
11k views

How do I add IPv6 address into System32\drivers\etc\hosts?

There is already by default, and it works (Win 7): ::1 localhost This also works (testing with ping): ::1 hosta But when I'm trying to add something non-loopback, it ...
12
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3answers
329 views

Registrar Name Server Change

When someone changes their authoritative name servers via their registrar, what process does the registrar go through to update the top-level domain (TLD) servers?
12
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1answer
2k views

How does DNS nameserver fall back work?

We have two DNS servers listed in our NS record. Last night, one of our DNS servers went down. As expected, some DNS servers were not resolving our hostnames. I assumed this would be temporary and ...
12
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1answer
377 views

How to force an ISP to remove false reverse DNS?

There is an IPv4 address (in a /8 managed by ARIN) that I have no control over which reverse resolves to a domain name which I registered. Someone used the IP address to run a scam, and it is ...
12
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1answer
2k views

How to set up Google ShortName service for my domain, so that the FQDN isn't needed

The blog post "A 'tinyurl' service for your domain" explains how to set up a ShortName service for your domain using Google Apps. For example, if your domain is example.com and you use Google Apps, ...
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8answers
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Blocking Facebook and Myspace by IP address

I'm having some trouble making a Cisco ASA device block certain social networking sites which have become time sinks in our office. This question is really in two parts: Is there a reliable way to ...
11
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4answers
592 views

How to switch DNS for a website without service disruption?

I would like to switch the DNS of our website without any service disruption The server IP stays the same. Usually it takes 24-48 hours to update the whole internet. Is it possible to have both DNS ...
11
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4answers
6k views

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?
11
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4answers
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DNS recursion is insecure, but necessary for internal applications?

In management of a Windows Server 2008, the server hosts DNS (is nameserver) for some domains, as well as hosting some applications that are publicly accessible. A security scan has indicated that ...
11
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3answers
14k views

How do you check if a nameserver responds to recursive queries?

I am just curious if you could use dig to check if a certain nameserver responds to recursive queries. Thanks!
11
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1answer
482 views

What is an open DNS resolver, and how can I protect my server from being misused by hackers?

I don't have the strongest background in computer security, but yesterday one of my company servers was shut down by our host. It's a server assigned a public IP where I host several web-service ...
11
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1answer
1k views

How long does negative DNS caching typically last?

If a DNS server looks up a record and it's missing, it will often "negatively cache" the fact that this record is missing, and not try to look it up again for a while. I don't see anything in the RFC ...
11
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4answers
7k 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 ...
11
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2answers
383 views

Why is my domain controller causing my router to send advertisements for Unique Local Addresses?

I'm currently evaluating Server 2012 to serve as a domain controller in a small heterogeneous network of Linux and Windows workstations and servers, all of which would eventually be joined to the ...
11
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3answers
790 views

Can I use the character ñ in a sub-domain?

We are launching our website in Spanish and are probably going to call it espanol.mydomain.com Since the real spelling is español, ideally we would allow people to type español.mydomain.com. Is ...
11
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7answers
3k views

Check public DNS health and RFC compliance

Every now and again I like to run checks on my DNS servers to make sure they are running right and to RFC spec. I used to use the DNSTools website to do this as it gave me a pretty good picture of ...
10
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8answers
3k views

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 ...
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6answers
2k views

Recommended DNS TTL

I know it could be very different based on the situation, but for hosting a website with no plans to move the hosting server what is a good TTL to set on the DNS record?
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4answers
15k views

How long will an MX record and A record change take when DNS server is not being changed?

I am trying to estimate whether it is realistic for me to change the IP of a mail server overnight or will this mess with people retrieving their email the day after. Basically, the facility where the ...
10
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6answers
18k views

Multiple Reverse DNS Entries?

I'm a DNS noob, so here's a question: Can a server have multiple reverse DNS entries? Or does one IP address just resolve to one DNS name? Here is why I need this: I have a number of sites hosted ...
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12answers
15k views

HOSTS file being ignored

My (Windows XP, Professional, v2002, SP3) workstation is completely ignoring my hosts file. Here is the code in my hosts file: 127.0.0.1 localhost 172.17.1.107 wiki But, when I open a ...
10
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8answers
4k 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 ...
10
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4answers
14k views

Can a CNAME DNS record point to a subdirectory

Can a DNS record point to an address like my.domain.com/subdir1
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10answers
14k views

DNS Name lookup (was SSH) Not Working After Snow Leopard Upgrade

I think this started with the Snow Leopard update. Cleaned out the .ssh directory, still having the issue. ~: uname -a Darwin california-example-com.local 10.0.0 Darwin Kernel Version 10.0.0: Fri ...
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4answers
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How to create a CNAME for a domain's root name

I'd like to set a domain's root name to a CNAME instead of the usual A record. Here's a perfect example of what I'm trying to do: dig lrnskls.com Notice the answer section: ;; ANSWER SECTION: ...
10
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6answers
3k views

Can you Recommend Free DNS Name Servers? [closed]

I'm currently looking for a decent DNS zone & record manager an would love some recommendations. The host for these sites doesn't offer anything, but something as simple as Slicehost's DNS ...
10
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1answer
904 views

Amplified reflected attack on DNS servers

The term Amplified reflected attack is new to me, and I have a few questions about it. I've heard it mostly happens with DNS servers - is that true? How do you protect against it? How do you know if ...
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3answers
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Do SPF Records For Primary Domain apply to subdomains?

I have a quick question regarding SPF records: Do they need to be present for all subdomains? Lets say that I have a TXT record with SPF info for domain.com Let's also say that I have a seperate ...
10
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2answers
20k views

How to list all CNAME records for a given domain?

I cannot list them using dig/nslookup/host.
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3answers
5k 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 and how does it work? Assuming an environment with multiple domain controllers ...