[an error occurred while processing this directive] FAQ Internet begreber dansk/engelsk
Michael Maardt: PC siden 1984 • på nettet siden 1990. Over 200 sider.

FAQ DNS, nameserver, a-record, CNAME, MX record ...

Juni 2011, Michael Maardt, sidst opdateret: 01.04.2016

THIS PAGE IS A DANISH/ENGLISH MIX

The page is mostly for myself trying to learn all this DNS stuff, but maybe you find something useful ;-)

Hvis du er landet her fordi du hber at forst DNS begreber, s har du det mske som jeg havde det dengang. Jeg har oplevet meget p nettet, men dette er det vrste. Frst da jeg startede med at have et webhotel flte jeg mig tvunget til at forst DNS begreberne. Hold da kft, hvor har mange forfattere beskrevet disse ord, begreber osv. elendigt, s hvis du har det sdan, er du ikke alene.

Jeg er mske lidt dum og langsomt opfattende, men hvor har jeg brugt lang tid p at fatte dette.

 

Navneserver nameserver

En navneserver er efter min mening en rigtig drlig betegnelse. Navneserveren indeholder skaldte DNS records, og disse udgr hvad der minder om en tabel med to kolonner. I den venstre kolonne str noget, der peger p noget andet i den hjre kolonne, altsammen med det forml at finde hen til en bestemt sted p en bestemt computer/server. En adresse kan vre www.knowware.dk

Navneservere bearbejdes typisk hos registratoren af domnenavnet, men ofte er et firma bde webhotel og domneregistrator.

Internation domain admin

ICANN is the global, non-profit, private-sector coordinating body acting in the public interest. ICANN ensures that the DNS continues to function effectively – by overseeing the distribution of unique numeric IP addresses and domain names. Among its other responsibilities, ICANN oversees the processes and systems that ensure that each domain name maps to the correct IP address.

DNS

DNS er et system eller service. DNS betyder Domain Name Service eller Domain Name System og bruges til at overstte (resolve) domnenavne som f.eks. knowware.dk til IP Addresses. En IP adresse er en unik adresse, som computere p internettet bruger til at identificere hinanden. Eksempel p en IP adresse er 213.175.216.244.

DNS is a huge global network based on 13 root name servers in different geographical locations and stretching out to thousands of individual name servers across the world. DNS is the very heart of the internet, and makes the internet as user friendly as it is today.

Hver gang DNS-serveren fr en anmodning om en web-adresse, slr den web-adressen op i sin database og finder den tilhrende IP-adresse.

DNS-zoner

DNS er baseret p filer. Disse filer indeholder zone-data. I mange tilflde indeholder hver fil/zone t domne. Derfor kan man betragte "zone" som synonym for "domne".

Den ansvarlige administrator for en zone findes i zonens SOA-record, Start Of Authority

Name Servers use Zone Files to store specific information about a domain name, such as the address of name servers or the address of the email servers which handle email for that particular domain. At the start of your zone file you will see a SOA record, Start of Authority.

This lists the email contact for the zone (usually a system administrator at the ISP/Registrar), the primary name server for the domain name and technical information such as Time To Live etc. The Time To Live entry defines how long the information is valid for and is not something you need to worry about.

 

Domain Name

Domain names are easy-to-remember names (URLs and email addresses) that are associated with one or more IP addresses. Since a web page is defined by its URL, the page can move to a different IP address without affecting visitors.

Example: www.singlespeed.com

  • singlespeed.com is the domain name
  • com is the top level domain
  • singlespeed is a subdivision of com, and represents the second-level domain
  • www is a subdomain, also known as third-level domain or CNAME

 

Domain Registrar

Domain registrars sell Internet domain names (ex. blueshirt.com or organicfood.org ).

If your domain registrar is separate from your domain host, you'll need to add the host's name servers to your registrar's account. For example, if you purchase a domain name from namecheap.com (which offers domain registration) and host your domain with DynDNS (which offers domain hosting), you'll add the name servers of DynDNS (ns1.mydyndns.org and ns2.mydyndns.org) to your account with namecheap.com.

 

Top Level Domain

Top-level domains are the last part of a domain name, the letters after the last period. Examples are: biz com org edu us dk ca fr de travel local es pl

 

Second-level Domain

Second-level domains are directly below top-level domains. Examples:

    Second-level Domain Domain Name
    Wikipedia wikipedia.org

 

Third-level Domain

Third-level domains are also known as subdomains or CNAMEs. In a URL, the subdomain is written before the domain name. Examples:

    Subdomain URL
    www http://www.rockfound.org
    men http://men.style.com

 

IP address

IP stands for Internet Protocol. Every computer on the Internet has a unique address - just like a telephone number - which is a string of numbers. 213.175.216.244 is an IP address.

 

How do I register a domain name?

Domain names ending with .aero, .biz, .com, .coop, .info, .museum, .name, .net, .org, or .pro can be registered through many different companies known as registrars that compete with one another. A listing of these companies can be seen internic.net in their Registrar Directory.

Registrar

The registrar you choose will ask you to provide various contact and technical information that makes up the registration. The registrar will then keep records of the contact information and submit the technical information to a central directory known as the "registry." This registry provides other computers on the Internet the information necessary to send you e-mail or to find your web site. You will also be required to enter a registration contract with the registrar, which sets forth the terms under which your registration is accepted and will be maintained.

Kan jeg redelegere et .dk domne andre steder end dk-hostmaster?

Nej. En redelegering kan godt startes et andet sted (f.eks. hos et webhotel end en DNS service), men den endelige redelegering sker frst, nr brugeren efter login hos dk-hostmaster.dk har accepteret redeleringen.

Hvem kan oprette et .dk domne?

Det kan en skaldt registator (eng. registrar). En registrator registrerer et .dk domne gratis. Brugeren (ejeren af domnet) betaler en rlig afgift p 45DKK til dk-hostmaster


Nr du kber et domne med webhotel skal domnet pege p webhotellet, sledes at en bruger der indtaster dit domne i en browser bliver frt til serveren hvor din hjemmeside ligger. Hvis du kber domne og webhotel sammen sker dette normalt automatisk. Hvis du senere tilkber et nyt domne eller skal pege domnet over p en anden server, skal du vide noget om DNS opstning.

DNS er en forkortelse af Domain Name System, som er et hierarki af navneservere, der overstter domnenavne til IP-adresser.

I adresselinien i din browser str der nu www.etnavn.dk, og dette navn er knyttet til eller peger p IP-adressen 91.102.88.75. Dette er umiddelbart skjult for dig som bruger, men din browser har fet tilsendt IP-adressen fra en navneserver.

Hvis du vil flytte din hjemmeside fra en server til en anden eller ndre hvilken mail server der skal modtage mails fra domnet, skal du rette DNS opstningen for domnet. Det er meget forskelligt hvilke vrktjer de enkelte webhotel-udbydere stiller til rdighed for DNS opstning. I nogle tilflde fr du slet ikke adgang til DNS opstningen og du skal s have fat i supporten for at f ndret DNS opstningen for dit domne.

Uanset hvordan du foretager DNS opstningen for dit domne skal du rent teknisk have oprette eller ndret de skaldte DNS records for domnet.

DNS records

DNS systemet indeholder mange forskellige typer DNS records (svarer til et kartotekskort), de vigtigste:

  • A-record
  • CNAME-record
  • MX-record

 

A-record

En A-record angiver laver en forbindelse mellem et domnenavn og en IP adresse

michaelmaardt.com -> 91.12.34.3

Det kan se sdan ud i unix jargon: michaelmaardt.com IN A 91.12.34.3 (A str for A-record'en)

CNAME-record

CNAME betyder Canonical Name og alias. En CNAME-record angiver et ALIAS for en A-record.

michaelmaardt.com IN A 192.168.0.5 (her opns domnenavnet peger p en a-record, som er en IP-adresse for serveren, hvor hjemmesiden befinder sig

www IN CNAME michaelmaardt.com
ftp IN CNAME michaelmaardt.com

 

MX-record

En MX-record angiver Mail eXchange for domnet, hvilket er den mailserver der skal modtage domnets emails.

Mailserverne angives i prioriteret rkkeflge og typisk angiver man to mailservere sledes at mails ikke gr tabt, hvis en af serverne ikke svarer.

En MX-record angives i DNS p formen:

Vrt (host)   Mail udveksler (mailserver)   Prioritet TTL   Time-To-Live
minhjemmeside.dk   mail1.server.dk   10   14400
minhjemmeside.dk   mail2.server.dk   20   14400

Man m IKKE lave en MX-record som peger p en CNAME-record! En MX-record skal altid pege p en A-record.

Time To Live

TTL (Time To Live) angiver i sekunder, hvor lang tid et DNS opslag skal caches p navneservere og brugernes computere. I ovenstende eksempel er TTL sat til 14.400 sekunder, hvilket svarer til 4 timer. Det betyder at der gr op til 4 timer fr en DNS ndring vil sl igennem p computere og navneservere der har cachet den p gldende DNS record. Typisk vil man stte TTL mellem 4 og 24 timer.

Stter man en lan TTL vil navneserverne blive belastet med flere opslag og stter man en hj TTL skal navneserverne ikke foretage s mange opslag. Derfor er den eneste situation, hvor det giver mening at have en lav TTL, hvis du skal flytte hjemmeside fra en server til en anden. Ved at stte lavt 24 timer fr flytter din hjemmeside vil ndringen af DNS sl igennem med det samme, og hvis du har lavet en fejl kan du hurtigt skifte tilbage. Nr alt er testet kan du igen stte TTL hjt. Hvis du flytter din hjemmeside mens der er en hj TTL er der lang reaktionstid og du har ikke samme mulighed for at skifte tilbage, hvis du har lavet en fejl.
DNS vrktj

Nr man arbejder med DNS opstning har man tit brug for at lave forskellige DNS opslag. Til det forml kan man bruge nslookup som er en del af Windows, men som kun er for den erfarne bruger. Hvis du fortrkker en grafisk brugergrnseflade kan jeg varmt anbefale DNSstuff.com, der tilbyder et en lang rkke DNS vrktj og DNS alarmer.

Endelig vil jeg anbefale dig at lse artiklen “Sdan flytter du dit site til en ny IP uden overraskelser“, der giver en opskrift p optimal skift af IP adresse.


When you create a new account in WHM it means you are hosting a new account on your server. Example: you have created a new account named abc.com that means you are hosting abc.com on your server. The domain name (abc.com) should be a registered domain name with any authorized domain name registrar. So for any functional website these two parts are basic and necessary.

Every domain has its own DNS zone file which is hosted by DNS service provider. Any server incl. own server can provide this DNS service. The DNS zone file contains all its associated DNS records about the domain name where it is located, which email server it uses, nameservers.

The common fields and description are as follows.

$ORIGIN abc.com. designates the start of this zone file in the namespace
$TTL 1h default expiration time of all resource records without their own TTL value
abc.com. IN SOA ns.abc.com. username.abc.com. (  
2007120710 serial number of this zone file
1d slave refresh (1 day)
2h slave retry time in case of a problem (2 hours)
4w slave expiration time (4 weeks)
1h maximum caching time in case of failed lookups (1 hour)
)  
abc.com. NS ns ns.abc.com is a nameserver for abc.com
abc.com. NS ns.somewhere.example. ns.somewhere.example is a backup nameserver for abc.com
abc.com. MX 10 mail.abc.com. mail.abc.com is the mailserver for abc.com
@ MX 20 mail2.abc.com. equivalent to above line, "@" represents zone origin
@ MX 50 mail3 equivalent to above line, but using a relative host name
abc.com. A 192.0.2.1 IPv4 address for abc.com
AAAA 2001:db8:10::1 IPv6 address for abc.com
ns A 192.0.2.2 IPv4 address for ns.abc.com
AAAA 2001:db8:10::2 IPv6 address for ns.abc.com
www CNAME abc.com. www.abc.com is an alias for abc.com
wwwtest CNAME www wwwtest.abc.com is another alias for www.abc.com
mail A 192.0.2.3 IPv4 address for mail.abc.com,
any MX record host must be an address record
as explained in RFC 2181 (section 10.3)
mail2 A 192.0.2.4 IPv4 address for mail2.abc.com
mail3 A 192.0.2.5 IPv4 address for mail3.abc.com

While browsing abc.com it will only show the contents it has on the hosting server. In the DNS zone file of abc.com, If the "A" records are defined to point to your server it will display the same contents it has on your server. The contents are stored in the domain's web root folder.

Regarding you specific questions:

"Registrar for michaelmaardt.com is enom.com I bought via hostgator.com I also bought michaelmaardt.net at godaddy. They have a much better DNS interface, where I can do everything with records. I cannot do this at hostgator. A transfer from enom to godaddy would cost me $8, is that worth?"

>> >> It all depends on you. If it has more function to define new DNS records and you required them then you may want to switch or else it doesn't need to move if the existing registrar has all basic/common options.

"My problem most of the time has been to understand the nameserver, what is is, where it is and what it contains and what it does. Now I understand more than I did 5 days ago. I am wondering what is the diff. between all the records I can set up at godaddy, I can make a-records, cnames etc but apparently I can make the same in WHM, Edit DNS zone, correct? Which of those has highest authority? "

>> >> For any domain name it has DNS records at domain registrar end and in the DNS zone file which is hosted by DNS service provider. Generally it only needs "NS" records to be same at both ends (at registrar end and in DNS zone file). All DNS functions should be handled through WHM >> Edit DNS zone (If you have your own nameservers setup on the same server).

Thus the hosting server will have the A records assigned for the custom nameservers in its DNS record. This custom nameservers should be registered at registrar end in order to use it. Since the domain registrar is Enom you need to contact them and in the Domain Management Panel which they offer for the domain, there is an option to register the custom nameservers.