Welcome to 3rdPartyDNS.com
The Domain Name System (DNS)
associates various sorts of information with so-called
domain names; most importantly, it serves as the "phone
book" for the Internet by translating human-readable
computer hostnames, e.g. www.example.com, into the IP
addresses, that networking equipment needs to deliver
information. It also stores other information such as
the list of mail exchange servers that accept email for
a given domain. In providing a worldwide keyword-based
redirection service, the Domain Name System is an
essential component of contemporary Internet use.
DNS (Domain Name Server) Terminology
| Term | Description |
|---|---|
| A Record | Address Record, assigns an IP address to a domain name. When the domain name system was designed it was recommended that no two A records refer to the same IP address. This is not practical due to the limitations of CNAME records. |
| Alias | See CNAME record. |
| Ancestry | Term used to describe zones and domain names. Root, written as "." is the ultimate ancestor zone. All top level domains like com, gov, and org are all its children. example.com is the child of com. gomer.example.com is the child of example.com. Com is an ancestor of gomer.exaple.com, as is ".". Another way to think of children is as subdirectories (delegations) of parent directories, or as folders within folders. |
| Authoritative | Adjective describing a name server or a response from a name server that is referencing its own native data. The authoritative server contains an entire copy of the zone that is derived from local configuration data, possibly with the help of another authoritative name server for the zone. Data is obtained without the need for caches or the help of any resolver. A server can be authoritative about one zone but not authoritative for another. |
| BIND | Berkeley Internet Name Daemon. The most common DNS software of the internet. Ported to every flavor of Unix and Windows NT (Windows is a Trademark of the Microsoft Corp.). Bind source code is maintained by the Internet Software Consortium. |
| Caching | The act of recording authoritative response to resolver queries for future reference. Generally cached records will be purged after a predetermined time. |
| Canonical Name | The real name of a host. Used in CNAME records, PTR records, NS records and MX records. A canonical name is something of a fiction because many servers have more then one equally valid name. Basically, any domain name that has an A record. |
| CIDR | Classless Inter Domain Routing. Currently
subnets are defined by the number of binary bits
they have in common. This replaces the older
subnet class system. Each octet of the IP
address can be broken down into two hexadecimal
digits; it takes 8 bits to represent each pair
of hexadecimal digits. So a class A subnet which
shares the first octet would be an 8 Bit subnet.
A class B would be a 16 Bit subnet. A class C
subnet would be a 24 bit subnet. If your ISP provides you with a subnet you will likely have many more bits in common. For example, if you were given a 29 bit subnet, you would have 8 IP addresses, an Identifier address, 6 useable IP addresses, and a broadcast IP address. |
| Class A Subnet | A subnet that shares the first octet. |
| Class B Subnet | A subnet that shares the first and second octets. |
| Class C Subnet | A subnet that shares the first, second, and third octets. |
| CNAME Record | Canonical Name Record. Creates an alias of a canonical name. The alias gains all properties of the original, including IP addresses and mail routes. Because of this, it is illegal for there to be any other record with the same owner name as a CNAME record. It is also illegal for any record other than a CNAME record to refer to an alias. |
| Delegation | The process of separating a descendant of a zone into a separate zone. The delegation is accomplished with NS records and if necessary, A records. NS records used for this purpose are called "delegation records", A records used for this purpose are called "glue records." Records in a delegation are an exception to the rule that a record should only be defined only in the zone that owns the name of the record. |
| Dig | Similar to nslookup. Another command line tool for querying DNS servers. Somewhat unwieldy, bundled with BIND. Like all Unix terms, dig is case sensitive and must always be used in lower case. |
| DNS Server | A DNS Server is any piece of software that serves as a name server, a resolver, or both. |
| Domain | Most often used to refer to a domain zone,
domain is also used to describe a zone, or a
domain name. This ambiguity results in an
unbelievable number of technical support
questions, and is a driving force in the sales
rate of "DNS and Bind." |
| Domain Zone | Any zone that isn't a reverse zone. Root is an exception; root is not a domain zone. Sometimes called a forward domain, or forward zone. This terminology came about because of the ambiguity of the word domain, and use of the term reverse domain, which is now considered archaic. |
| Dynamic IP Address | A Dynamic IP address is one that is
temporarily assigned to a user by their internet
service provider every time the connect. This
cuts down on the number if IP addresses large
consumer providers need because not all of their
customers are using the service at any given
time. It also cuts down on bandwidth usage by
preventing consumers from hosting servers. Note:
Recently a number of companies have started to
offer services aimed at updating DNS for
dynamically connected clients. |
| Expire Field | Sixth field in an SOA record. Measured in seconds. If the refresh and retry attempts fail after that many seconds the server will stop serving the zone. Typical value is 1 week. Not used by a primary server. |
| Forward Domain | Archaic, See Domain Zone |
| Forward Zone | See Domain Zone. |
| Forwarding | The process of sending a recursive query
sent from a host to a resolver, to a second
predetermined resolver. Reasons for forwarding
might involve a resolver having little or no net
access, or if one resolver has a significantly
larger cache. |
| Fully Qualified Domain Name | A domain name that extends all the way back to root. Often written as FQDN. gomer.gimboid.com. is an FQDN. A common error is to leave the "." at the end off. gomer.example.com is NOT an FQDN, by leaving out the last "." Root is not included. An FQDN is required any time you reference a domain name outside a zone, optional when referencing names inside the zone. CNAME records, NS records, and MX records might refer to names outside the zone, they often require an FQDN. |
| Fully Qualified Host Name | See Fully Qualified Domain Name. |
| Glue Record | A glue record is an A record that is created
as part of a delegation. If a zone is delegated
to a name server whose hostname is a Descendant
of that particular zone, then a glue record for
that hostname must be included in the
delegation. |
| Hexadecimal | Base 16 math. Computers normally "think" in base two math, called binary. The only two digits are 1 and 0. So in binary the number 5 would be represented by. 101 (1 in the fours place, and one in the ones place.) This binary thinking is generally translated into base 16 math. That is to say, you can have a single digit number as high as 15. Single digit numbers higher then 9 are usually represented by letters A-F. So the hexadecimal number C5 translates to 197 in normal base 10 math; 12 in the 16's place and 5 in the ones place. |
| HINFO Record | Host Information Record. Strictly informational, not functional. Used to declare the computer type and operating system of a host. |
| Host | A host is any machine on any network. On TCP/IP networks, each host has one or more unique IP addresses. |
| Hostname | A Hostname is any domain name that has one or more IP addresses associated with it. The association is created by placing an A record in the zone that owns the domain name. Zone A owns domain name D if: There are no other zones in the line of ancestry between A and D. |
| IP Address | A unique identifier number for any host on any TCP/IP network, including the Internet. An IP address is made up of four octets. Each octet has a value between 0-255 |
| Iterative query | A request, usually made by a resolver, for any information a server already has in memory for a certain domain name. |
| Label | An element of a domain name. No label can be longer then 63 characters. Labels are made up of letters, numbers and hyphens, but may not start with hyphens. Labels in a domain name are separated from each other by "."'s. Labels are case insensitive. For Example: WWW.All.These.8.labels.are.very-good.gov |
| LOC Record | Location Record. Experimental, proposed in
1996. Informational, not functional. Used to
give latitude and longitude, in degrees minutes
and seconds, altitude in meters, and dimensions
(in terms of meters) of a host. Of no practical
use except to hi-tech thieves with a GPS tracker |
| Machine | See Host. |
| Mail Relay | The process of sending a message from one point to another through an intermediary. Any mail server that supports this should have some kind of filter system in place to avoid unauthorized use by spammers. Mail servers without this protection are open to hijacking. More on mail relay. |
| Master Server | See Primary Server. |
| Minimum Field | Seventh field in an SOA Record. The default
TTL for every record in the zone. Can be
overridden for any particular record. Typical
values range from eight hours to four days. When
changes are being made to a zone, often set at
ten minutes or less. |
| MX Record | Mail Exchange Record. Creates a mail route
for a domain name. A domain name can have
multiple mail routes, each assigned a priority
number. The mail route with the lowest number
identifies the server responsible for the
domain. Other mail servers listed will be used
as backups. |
|
Name Server |
A name server is software that runs on a
host that can be set to authoritatively answer
queries for records in a zone. |
| Node | See Host. |
| NS Record | Name Server Record. An NS record declares that a given zone is served by a given name server. Every NS record is either a delegation record or an authority Record. If the name of the NS record is the name of the zone it appears in, it is an authority record. If the name of the NS record is that of a descendant zone, then it is a delegation record. |
| NSlookup | Standard tool for querying name servers in
command line operating systems like Un*x and NT. |
| Octet | An octet is one of the four numbers making
up an IP address. Octets values can range from 0
to 255. Each octet can be expressed as 8 binary
bits, hence the name octet. An octet can also be
represented by 2 digits of Hexadecimal. |
| Origin | The ancestor that is appended to an
unqualified domain name to form a fully
qualified domain name. Usually set to the zone
name. |
| Owner | A zone owns itself and all descendant names
that are not delegated. A server for a zone can
respond authoritatively for any domain name
owned by the zone. |
| Primary Field | The first field of an SOA record. This field
is informational only and has no function. It is
intended to hold the hostname of the primary
server. |
| Primary Server | Also called a master server. An
authoritative name server that gets its zone
data from local configuration, not from an
outside source. This term is used in terms of a
specific zone. The primary server of one zone
could be a secondary server in regards to
another zone. Despite a common misconception,
from a resolver's point of view, primary and
secondary servers are equal in authority and
priority. |
| PTR Record | Pointer Record. Also called a reverse
record. A PTR record associates an IP address
with a canonical name. PTR records should point
to a name that can be resolved back to the IP
address. The name of the pointer record is not
the IP address itself, but is the IP address'
four IP octets in reverse order followed by
IN-ADDR.ARPA. for Example: 192.168.0.1 becomes
1.0.168.192.IN-ADDR.ARPA. |
| Record | See, Resource Record. |
| Record Class | There are three schemes for record systems,
Internet, Hesiod, and Chaos. Hesiod is only used
at M.I.T, and maybe not even there anymore.
Chaos is almost extinct, BIND uses it to check
its version number, but that's about it.
Internet is the system that 99.999% of servers
use. |
| Recursive Query | A recursive query is a request from a host
to a resolver to find data on other name
servers. |
| Refresh Field | Fourth field in an SOA record. Refresh
determines the number of seconds between a
successful check on the serial number on the
zone of the primary, and the next attempt.
Usually around 2-24 hours. Not used by a primary
server. |
| Resolver | A resolver is a host capable of performing a
recursive search of the Domain Name System to
locate records that would answer a query. It
does this by querying name servers, including
the root servers. In other words, a resolver is
a DNS server that looks up DNS records on behalf
of a client machine. |
| Retry field | Fifth field in an SOA record. If a refresh
attempt fails, a server will retry after this
many seconds. Not used by a primary server. |
| Reverse Domain | Archaic, see Reverse Zone. |
| Reverse Record | See PTR Record. |
| Reverse Zone | A reverse zone is a zone whose purpose is the mapping of IP addresses to names. Nearly all reverse zones are descended from the IN-ADDR.ARPA zone. |
| Root Server | There are currently 13 servers that are
authoritative for the root zone. They are named
a.root-servers.net - m.root-servers.net. Every
resolver must have the IP addresses of one or
more of these root servers coded in so that it
can resolve domain name. |
| Root Zone | The ancestor of all zones, the parent of the
top level domains. It is written as ". ". Root
(as it is often called) has no labels. |
| RP Record | Responsible Person. Informational, not functional. Used to indicate the person responsible for the domain. |
| Secondary Server | Sometimes called a slave server: A secondary
name server is an authoritative name server that
gets its data from outside sources, usually a
zone transfer from a primary server. This term
only applies to relations with a specific zone,
a secondary server for one zone could be a
primary for another. Despite a common
misconception, from a resolvers point of view,
primary and secondary servers are equal in
authority and priority. |
| Serial Number Field | Third Field in an SOA record. Used by a
secondary server to determine if it requires a
zone transfer from the primary server. If the
Secondary's Number is lower than the Primary's,
then the secondary server knows that its records
are out of date. Not used by a primary server. |
| Server | See Secondary Server. |
| SOA Record | Start of Authority Record. The SOA is the
first record in every properly configured zone.
The SOA record contains information about the
zone in a string of fields. The SOA record tells
the server to be authoritative for the zone. |
| Static IP Address | A static IP Address is an IP addressis an IP
address assigned by a service provider that
never changes. This requires that the service
provider keep at least one IP address per
customer. Because their IP address remains
fixed, static IP addresses can be used for
hosting name servers. |
| Subdomain | Any child of a domain zone. |
| Subnet | A contiguous string of IP addresses. The
first IP address in a subnet is used to identify
the subnet, the last IP address in the subnet is
always used as a broadcast address. Anything
sent to the last address is sent to every host
on the subnet. |
| Subnet Class | Traditionally subnets have been broken down
into three size classes based on the 4 octets
that make up an IP address. For example:
123.001.002.178. Class A was any subnet that shared the first octet. Apple for example has a class A subnet. The first octet was 0017. All IP addresses starting with 17 are controlled by Apple. A class A subnet has over 16 Million possible IP addresses. Apple thus effectively controls 1/255th of the Internet. Class B subnets share the first two octets. Class C subnets share the first three octets, effectively giving a class C subnet 254 possible IP addresses. (Remember that the first and last IP addresses are used as a network number and a broadcast address.) |
| TLD | See Top Level Domain |
| Top Level Domain | Any zone owned by the root servers. You can
also think of this as the first label in any
domain name other than root (which has no
labels) For Example: com, edu, gov, mil, net, org, int, arpa, country codes. |
| Tree | A common analogy for the branching structure
of the Domain Name System. Under this analogy
various domain names are referred to as nodes. |
| TTL | Time To Live, the number of seconds
remaining on a cached record before it is
purged. For authoritative records the TTL is
fixed at a specific length. If a record is
cached, the server providing the record will
provide the time remaining on the TTL rather
then the original length it was given |
| TXT Record | Text Record: Strictly informational, not
functional. Used to provide up to 255 characters
of free form text, hopefully about the zone.
Multiple TXT records are permitted but their
order is not necessarily retained, a bad forum
for presenting War and Peace. |
| Unqualified Domain Name | A domain name that is intentionally written incompletely with the understanding that some ancestor domain name will be appended to form a fully qualified domain name. |
| WKS Record | Well Known Service Record. Experimental, not yet adopted or used by any browser. WKS is generalized version of the MX record. Which is not just for mail but for any service. Examples would be POP, HTTP and FTP. If adopted, it will allow greater flexibility in resolving names from IP addresses and will lessen some of the problems cause by native round robin load sharing in servers. |
| Zone | Any domain name that has been delegated by an ancestor zone. Also includes all descendant domain names that have not been delegated. |
| Zone Transfer | A special type of query that asks a name server for the entire contents of a Zone. Cached records are never reported in a zone transfer. Zone transfers are usually used by secondary servers to update its own zone data from its primary server. |
