User`s manual

Appendix
190 TCP/IP AX3000 User's Manual
A.5 - THE DNS PROTOCOL
The DNS protocol (Domain Name System) allows names to be 'resolved' by the
AX3000. Resolving is retrieving an IP address associated with a name.
A.5.1 - Overview
A domain (computer network) can be considered as a tree, with branches
(nodes) such as hubs, switches, routers, print servers etc, and leafs, for
example PCs, terminals and printers.
The domain system makes no distinction between the use of interior nodes and
the leafs, and this documentation uses the term "nodes" to refer to both. (i.e.
any network resource).
Each node has a name (Label) which must be unique to other nodes at the
same level, but not necessarily unique within the whole network.
Label syntax:
- Permissible characters are letters (a..z to A..Z), numbers (0..9) and the
hyphen (-).
- A Label must begin by a letter and be ended by a letter or a number.
- The resolution is not case-sensitive.
The domain name of a node is the list of the labels on the path from the node to
the root of the tree. A dot is used to separate each label. Two types of host
names can be distinguished within the AX3000:
- A full name: one or more dots are included in the name.
Example: "www.axel.com"
- An incomplete name: no dots are used. The resolution procedure
concatenates, another character string to this name (the default DNS
domain name). For more information see Chapter 3.2.2.
Example: "as400" is concatenated with "servers.axel.com" to create a full
name of "as400.servers.axel.com"
A host name is only resolved if the IP address is needed. (i.e. to open a session
or to ping).
Note: a name is resolved for each connection attempt, even if its IP address