DOMAIN.SYS

Name

DOMAIN.SYS -- Hostname Resolution File.

Description

This optional file is used to "resolve" host names such as "g8jvm.ampr.org" and aliases such as "lgsbbs" into their corresponding IP addresses.

It is the first place XRPi looks when resolving a hostname. If the file is not present, or the hostname is not found in in the file, XRPi queries a DNS (Domain Name Server) to obtain the information (in order for this to work, either Linux or XRPi must have a network connection to a DNS).

If no DNS is available, and the hostname is not found in DOMAIN.SYS, you will have to enter the full IP address of the target host when using the PING, TELNET, TTY, and FINGER commands.

Name resolution using a Packet Radio DNS is quite slow, so if you are using this mode you should add entries to this file for frequently contacted hosts whose addresses are stable. Externally resolved names are added automatically to DOMAIN.SYS at regular intervals, and expired entries are purged.

File format

Each host is listed on a separate line. Each field must be separated by one or more spaces or tabs. Comments, spaces, tabs and blank lines are permissible to aid clarity. The records are case-insensitive, but most people use lower case for hostnames. The format of each record is as follows:

	<hostname> [ttl] IN A <ip-address>

	<alias>    [ttl] IN CNAME <hostname>
             
	<hostname> [ttl] IN MX [pref] <hostname>

The first form maps a hostname to an IP address, and the second and third forms map alternative hostnames to a host that is already defined.

For example, the IP address for the GB7PZT mailbox is 44.131.91.2 so it would have an Internet Address (IN A) record like so:

	gb7pzt  IN   A    44.131.91.2

But gb7pzt is also known locally as "pztbbs", and "kdrbbs". There is nothing to stop you adding further "IN A" records for gb7pzt, one for each alias, but you could instead use the second form shown above, the CNAME or "Canonical Name" record like so:

	pztbbs. IN CNAME  gb7pzt
	kdrbbs. IN CNAME  gb7pzt

Thus if the user types "TEL pztbbs" or "TEL kdrbbs", the gb7pzt record is used. This removes the need to keep repeating the IP address in multiple "A" records, and makes it easier if the IP address is changed.

The MX or "Mail Exchange" records are usually used for defining alternate names for mail servers, but as XRouter is not concerned with mail you can use them in the same way as CNAME entries, although there would be no point in doing so. The format of the additional records would be:

	pztbbs.   IN   MX   gb7pzt
	kdrbbs.   IN   MX   gb7pzt

The optional "preference" field of MX records is ignored.

The optional [ttl] field in all types of entry is the "time to live" of the entry in seconds, used to expire records whose addresses are liable to change. If omitted or set to zero, the record has an unlimited lifetime.

In order to simplify the file, the ".ampr.org" is usually omitted from the records, and appended automatically when the file is read. However, hostnames which contain or end with a dot will not be extended in this manner. Thus "gb7pzt" would be extended to "gb7pzt.ampr.org", whereas "lgs." and "ns.cyberphile.co.uk" would not be modified.

Notes

Although DOMAIN.SYS was originally designed to be simpler than the more standard DOMAIN.TXT format, Xrouter is capable of understanding both formats, so you may use an existing DOMAIN.TXT simply by renaming it to DOMAIN.SYS.

Files

DOMAIN.SYS is located in the same directory as XRPi.EXE.

Limitations

XRouter's DNS server currently responds only to type A queries.

See also

DNS(2) -- DNS Configuration Commands.