Guide to a Zone Listing
What you see below is an example of a "zone listing". A zone listing is simply a file that defines all of the information for an Internet Domain. The file is used by the DNS server to provide information about the domain to the world. Before tw telecom can set up a domain on our servers, we require the information contained in a zone listing.

Whether your are setting up a domain for the first time, or transferring a domain to our servers, we will need the information contained in the zone listing to complete the request. Please see one of the following documents for more information on making these requests:

Moving a Domain to tw telecom

Registering a Domain to tw telecom


Zone Listing Example and Explanation


$ORIGIN examplesite.com.
@         IN SOA ins1.milw.examplesite.net.      hostmaster.examplesite.net. (
  2000100400 ;Serial 1993,10,22,00th
  10800 ;Refresh
  3600 ;Retry
  604800 ;Expire
 

 86400 )

 ;TTL
  IN NS ins1.milw.examplesite.net.
  IN NS ins1.iplt.examplesite.net.
  IN MX  10 thelmalou
  IN MX  20 mx1.mail.examplesite.net.
 

 IN MX  30

 mx2.mail.examplesite.net.
localhost 

 IN A

 127.0.0.1
thelmalou  IN A 168.215.33.107
auntbea IN A 168.215.33.115
www  IN A 207.67.10.7
web 

 IN CNAME

 www


The SOA (Start Of Authority) record indicates which nameserver is the best source of information for the data within the zone. The next entry on that line is the email address of the person in charge of changing the data for the domain.

The Serial Number is only important for nameservers slaving the information about the domain. They determine if there is new information by comparing the serial number of their record against the serial number of the master nameserver. If the master's serial number is higher, this indicates new information and the slaves pull the new zone record so their information is matching. If the serial number is the same, or lower, than the serial number the slaves have, the zone is not pulled.

The Refresh number tells a slave how often (in seconds) it should check with the Master to verify it still has the correct information.

The Retry number tells a slave how often to attempt to contact the Master after a failure to connect when checking for new information.

The Expire time tells the slave when to stop serving information for the domain. If the slave is unable to reconnect to gather new information from the Master in that time frame, it will no longer give out information on the domain. This keeps the slaves from giving out stale information on a domain.

The TTL time tells other nameservers on the Internet how long they should cache the information on this domain. If you are planning a big change (such as a new mailserver on a new IP, or changing hosts for your webpage), it's best to set the TTL down to a shorter timeframe at least 2 days in advance of making the change. This will ensure that the new information is propagated across the Internet faster.

The NS records are a source of info about what other nameservers may know about this domain.

The MX records are where email for this domain is delivered. The lower the number, the higher the priority of the mailserver. In this case, all email for twtelecom.com will attempt to be delivered to the mailserver named thelmalou.twtelecom.com. Should thelmalou be unreachable, remote mailservers will attempt to deliver email to mx1.mail.twtelecom.net next, should mx1.mail.twtelecom.net fail, they will attempt mx2.mail.twtelecom.net. Only if all 3 mailservers fail will email be immediately bounced back to the sender. These 'extra' mailservers are referred to as 'backup MX.'

An A Record assigns a name (www i.e. www.twtelecom.com) to an IP (207.67.10.7).

A CNAME Record assigns a name (web i.e. web.twtelecom.com) as an alias to another name (www.twtelecom.com). As an IP should only have one A record pointing to it in a domain, aliases are the best way to assign multiple names to one IP.