Appendix B

Alias

Aliases are redundant names or nicknames that are assigned to already named internet Hosts. Aliases permit the association of multiple names to a single host. Aliases may be useful when a host provides several different services or to transition a host to a new name while preserving compatibility via the old name.

Domain

A Domain is a collection of Hosts that are typically related via some logical organization like geographic or political boundaries, government beuracracies, and corporate divisions. However, a Domain does not require a particular organization, any set of Hosts may be collected into a Domain. Note that Domains themselves may be divided into sub-Domains, and so on.

Domain Name

Domain Names are the names assigned to collections of Hosts on the Internet. A Domain may comprise any collection of hosts, but typically a Domain is associated with some logical organization like geographic and political boundaries, government beuracracies, and corporate divisions.

Domain Name Server

A Domain Name Server is a computer that shares its database of DNS Resource Records which are typically Host Names and IP Addresses with other Hosts and Domain Name Servers.

A small Domain Name Server may manage a small number of Zones, or a Zone comprising a single Domain, while a large Domain Name Server may manage a large number of Zones comprising several hundred Domains.

Domain Name System

The Domain Name System (DNS) is the address book for the Internet. The Domain Name System divides Hosts into collections called Domains much like Phone Numbers are divided into Area Codes. Note that Domains may themselves be divided into sub-Domains, and so on.

The Domain Name System distributes the administration of the Domains between a large number of Domain Name Servers.

There are several excellent online and printed Domain Name System References available on the Web.

Expire

The Expire value tells a Secondary Name Server how long to keep using a previously loaded database if the Secondary Name Server continues to fail to connect to a Master Server.

Host

A Host is the word used to refer to a computer. Typically the computer is connected to a network. Most Hosts are general purpose computers like Main Frames or PCs, but a Host may also be some other device like a Printer, an NFS Server, or a Router.

Host Information

Host Information is the name assigned to the collection of information or records that the Domain Name System manages for each Host.

Host Name

Host Names are the names assigned to internet Hosts. Host names are used in place of IP Addresses because they are much more readily remembered by humans.

Host Table

The Host Table is the name of the table displayed in the Primary Zone Page of the DNS Web Pages.

IP Address

IP Addresses (or Internet Protocol Addresses) are the internet address assigned to Hosts. They are usually represented in the Internet dot notation (e.g., 127.0.0.1 ), and are typically assigned to a particular host by a network administrator.

Machine Name

The Machine Name was originally intended to to identify a Host hardware type (from the list on page 82, MACHINE NAMES in RFC 1340 ) but this list is out of date. In practice the Machine Name is used to hold any information a Network Administrator chooses to record. Machine Names are automatically quoted (with double quotes) after being entered into the DNS Web Pages. Therefore, Machine Names may contain a space (" "), but must not contain a double quote (" " ").

Mail Exchanger

Mail Exchangers are the records used by the Internet Mail Service to specify the best destination for mail sent to a particular Host.

Master Server

A Master Server is a Domain Name Server that is used to load zone information into other Domain Name Servers. A Master Server may serve both Primary Zones or Secondary Zones (loaded from some other Master Server).

Minimum Time-To-Live

The Minimum TTL value is included by a Domain Name Server in the response to any query requesting a record from this Server. The Minimum TTL tells the sender of the query how long it is acceptable to cache this record.

Precedence

Each Mail Exchanger is assigned a precendence indicating the order in which the Mail Exchangers should be used when sending mail to a particular Host. Mail Exchangers with the lowest precedence are used first, and if they are unavailable to receive the mail, Mail Exchangers with the next lowest precedence are use next, and so on.

Primary Zone

A Primary Zone is a Zone that a Domain Name Server serves from its local database.

Refresh

The Refresh value tells a Secondary Name Server how long to wait before checking with its Master Server for changes in the Master Server's database.

Resource Records

Resource Records is the name assigned to the collection of information or records that the Domain Name System manages.

Retry

The Retry value tells a Secondary Name Server how long to wait before trying to reestablish a connection with its Master Server if the Secondary failed to contact the Master Server at the end of the Refresh period.

Reverse Lookup Zone

A Reverse Lookup Zone is a Zone that contains the "reverse" mappings of IP Addresses to Host Names. Reverse Lookup Zones are easy to identify because their Domain Names always ends with " .in-addr.arpa. ".

Reverse Lookup Zones may be either Primary Zones or Secondary Zones. Primary Reverse Lookup Zones are handled automatically by the DNS Web pages, and do not appear in the table of Primary Zones. Secondary Reverse Lookup Zones are handled exactly like normal Secondary Zones, and do appear in the table of Secondary Zones.

Secondary Zone

A Secondary Zone is a Zone that a Domain Name Server loads from some other Domain Name Server, called a Master Server.

Serial Number

Each DNS Zone database file is assigned a serial number. When Web Ten modifies a Zone, it increments the serial number in the SOA record in the Zone file. Secondary name servers recognize updates in Zone files by comparing the serial number of the local copy of the Zone file against the Master's serial number.

Start of Authority

Start of Authority is the name given to the information with governs how often Name Servers communicate with each other to ensure that the information they are serving is up to date.

The Start of Authority values for a Primary Zone on this system control how often other Domain Name Servers check with this system to verify that any cached information about this Zone is current.

The Serial Number, Refresh, Retry, and Expire values are used by other Domain Name Servers if they are acting as Secondary Servers for this Zone. These values control how ofter to check with the Master Server, how long to wait if the Master Server is unavaliable, and how long to keep serving any cached information if the Master Server remains unavailable.

The Minimum-Time-To-Live or Min TTL value is used by all Domain Name Servers that queries any piece of data within this Zone. The Min TTL tells these other Servers how long they may cache the data before checking back with this Server to see if the data has changed.

System Name

The System Name was originally intended to to identify a Host Operating System (from the list on page 86, SYSTEM NAMES in RFC 1340 ) but this list is out of date. In practice, the System Name is used to hold any information a Network Administrator chooses to record. System Names are automatically quoted (with double quotes) after being entered into the DNS Web Pages. Therefore, System Names may contain a space (" "), but must not contain a double quote (" " ").

Zone

A Zone is the portion of a Domain that is managed on a single Domain Name Server.

A Zone may comprise an entire Domain, or only a part of a Domain, but a Zone is the smallest or atomic unit (within Domains) that Domain Name Servers manage.