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NOSVIEW
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DOMAIN
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====== NOSview [301]
domain
======
The 'domain' commands control the-name-to-Internet-address
mapping software.
NOS translates domain names (e.g. "ns9bob.ampr.org.") to IP
addresses (e.g. "44.199.41.1") through the use of an Internet
Domain Name resolver and a local "cache" file, /domain.txt.
Whenever the user specifies a domain name, the local cache is
searched for the desired entry. If it is present, it is used; if
not, and if domain name server(s) have been configured, a query
is sent over the network to the current server.
If the server responds, the answer is added to the /domain.txt
file for future use. If the server does not respond, any
additional servers on the list are tried in a round-robin fashion
until one responds, or the retry limit is reached (see the
'domain retry' command).
If /domain.txt does not contain the desired entry and there are
no configured domain name servers, then the request immediately
fails.
If a domain name server is available, and if all references to
hosts in /autoexec.nos are in IP address format, then it is
possible to start with a completely empty /domain.txt file and
have NOS build it for you.
However, you may wish to add your own entries to /domain.txt,
either because you prefer to use symbolic domain names in your
/autoexec.nos file or you don't have access to a domain server
and you need to create entries for all of the hosts you may wish
to access.
Address Records
---------------
Each entry in /domain.txt takes one line, and the fields are
separated by any combination of tabs or spaces. For example:
ns9bob.ampr.org. IN A 44.199.41.1
The host "ns9bob" is in domain ".ampr.org.".
"IN" is the class of the record. It means Internet, and it will
be found in all entries.
"A" is the type of the record, and it means that this is an
address record. Domain name "ns9bob.ampr.org" therefore has
Internet address 44.199.41.1.
By setting the default domain to ampr.org. (with the command
'domain suffix ampr.org.') you can then talk to Bob with commands
like 'telnet ns9bob' or 'finger ns9bob'.
Canonical Name Records
----------------------
Another possible entry in /domain.txt is the "CNAME" (Canonical
Name) record. For example:
bob.ampr.org. IN CNAME ns9bob.ampr.org.
This says that domain name "bob" is actually an alias (or
"nickname") for the primary (or "canonical") domain name
"ns9bob". When a domain name having a CNAME record is given to
NOS, the system automatically follows the reference to the
canonical name and returns the IP address associated with that
entry.
Thus if you wish to use Bob's BBS, you may say either 'telnet
ns9bob' or 'telnet bob'.
Mail Exchanger Records
----------------------
Yet another type of entry supported by NOS is the "MX" (Mail
Exchanger) record. For example:
ns9zzz.ampr.org. IN MX 0 ns9mhb.ampr.org.
This states that mail addressed to ns9zzz is to be sent to ns9mhb
for onward transmission. The parameter "0" is the preference
value. Zero means highest preference.
There could be several records for ns9zzz, each with a different
preference value, and the mail forwarding program will attempt to
send the mail in order of preference. For example:
ns9zzz.ampr.org. IN MX 0 ns9mhb.ampr.org.
IN MX 10 ns9gwb.ampr.org.
IN MX 20 ns9gwc.ampr.org.
You can also use wildcards in these entries. For example:
ns9zzz.ampr.org. IN MX 0 ns9mhb.ampr.org.
*.ns9zzz.ampr.org. IN MX 0 ns9mhb.ampr.org.
The first entry handles mail addressed to ns9zzz, and the second
entry handles other hosts at ns9zzz (e.g. "pc.ns9zzz.ampr.org.").
**** In order to use MX entries, you need to give the command
**** 'smtp usemx on'.
Other Record Types
------------------
Additional types of records, include NS (name server) and SOA
(start of authority) may appear in /domain.txt from remote server
responses. These are not currently used by NOS but are retained
for future development (such as the incorporation of a domain
name server into NOS itself).
Time-to-Live
------------
Entries added automatically by NOS will have an additional field
between the domain name and the class (IN) field. For example:
ns9ken.ampr.org. 3600 IN A 44.199.41.2
This is the time-to-live value, in seconds, associated with the
record received from the server. Clients (such as NOS) caching
these records are supposed to delete them after the time-to-live
interval has expired, allowing for the possibility that the
information in the record may become out of date.
Most implementations of NOS will decrement the TTL to zero, but
will not delete the record unless the "clean" flag is on (see the
'domain cache clean' command).
When a remote server is not available, the old entry will be
used.
When the TTL value is missing, the record will never expire, and
must be managed by hand. Since /domain.txt is a plain text file,
it may be easily edited by the user to add, change or delete
records.
The 'domain' commands are now described:
_________________________________________________________________
domain addserver <host> [<host> ... ]
_________________________________________________________________
Add one or more domain name servers to the list of name servers.
Note that when this command is given in /autoexec.nos, the 'ip
address' command should given before any 'domain' commands are
used. (If not, no IP address is known to specify in the "from IP
address" and an answer will never be recognized, or worse, just
plain hangs the system).
>> Example: domain addserver ns9srv
_________________________________________________________________
domain cache clean [off|on] Default: off
_________________________________________________________________
Display or set the discarding of expired resource records.
Expired records have their timeout value decremented to zero.
Normally resource records get a default timeout value of 1800
seconds. After this time they are considered "old" and if
referenced again the domain name resolver should be enquired
again.
When 'clean' is off, expired records will be retained; if no
replacement can be obtained from another domain name server,
these records will continue to be used.
When 'clean' is on, expired records will be removed from the file
whenever any new record is added to the file.
>> Example: domain cache clean on
_________________________________________________________________
domain cache list
_________________________________________________________________
List the current contents of the local in-memory cache.
>> Example of output from the 'domain cache list' command:
..............................................................
: ns9mhb.ampr.org. IN A 44.199.41.6 :
: ns9zzz.ampr.org. IN MX 0 ns9mhb.ampr.org. :
: ns9gwa.ampr.org. IN A 44.199.41.4 :
: ns9bob.ampr.org. IN A 44.199.41.1 :
: nosland.ampr.org. IN A 44.199.0.0 :
:............................................................:
_________________________________________________________________
domain cache size [<entries>] Default: 20
_________________________________________________________________
Display or set the nominal maximum size of the local memory
cache.
Note: The cache may be temporarily larger when waiting for new
records to be written to /domain.txt.
>> Example: domain cache size 30
_________________________________________________________________
domain cache wait <seconds> Default: 300
_________________________________________________________________
Display or set the interval to wait for additional activity
before updating /domain.txt.
>> Example: domain cache wait 600
_________________________________________________________________
domain dropserver <host> [<host> ...]
_________________________________________________________________
Remove one or more domain name server(s) from the list of name
servers. You are warned when you delete the last name server.
>> Example: domain dropserver ns9srv
_________________________________________________________________
domain list
_________________________________________________________________
List the currently configured domain name servers, along with
statistics on how many queries and replies have been exchanged
with each one, response times, etc.
_________________________________________________________________
domain maxwait <seconds> Default: 60
_________________________________________________________________
This sets a timeout value (1 to 255 seconds) to a query or domain
name server. This is not set for an already defined server, but
will be used for a newly defined name server. Also the value is
used for domain nslookups. Note that name servers can have (PC-
based) trouble finding records in an large database.
>> Example: domain maxwait 120
_________________________________________________________________
domain query <host>
_________________________________________________________________
Send a query to a domain server asking for all resource records
associated with this <host>, and list the records.
>> Example: domain query ns9srv
________________________________________________________________
domain remote add <host> [<host> ...]
________________________________________________________________
Same as 'domain addserver'
_________________________________________________________________
domain remote drop <host> [<host> ...]
________________________________________________________________
Same as 'domain dropserver'
_________________________________________________________________
domain remote list
_________________________________________________________________
Same as 'domain list'.
_________________________________________________________________
domain remote retry [<n>] Default: 2
_________________________________________________________________
Same as 'domain retry'
_________________________________________________________________
domain remote trace [on|off] Default: off
_________________________________________________________________
Same as 'domain trace'
_________________________________________________________________
domain retry [<n>] Default: 2
_________________________________________________________________
Display or set the number of attempts to reach each server on the
list during one call to the resolver. If this count is exceeded,
a failure indication is returned.
If set to 0, the list will cycle forever; this may be useful for
unattended operation.
>> Example: domain retry 10
_________________________________________________________________
domain suffix [<domain_suffix>] Default: ampr.org.
_________________________________________________________________
Display or specify the default domain name suffix to be appended
to a host name when it contains no dots.
For example, if the suffix is set to ampr.org. and the user
enters 'telnet ns9bob', the domain resolver will attempt to find
ns9bob.ampr.org.
If the host name being sought contains one or more dots, however,
the default suffix is NOT applied (e.g. 'telnet foo.bar' would
NOT be turned into foo.bar.ampr.org).
If the suffix is an empty string, with no dot, the current suffix
is cleared.
>> Example: domain suffix ampr.org.
_________________________________________________________________
domain trace [on|off] Default: off
_________________________________________________________________
Display or set the flag controlling the tracing of domain server
requests and responses. Trace messages will be seen only if a
domain name being sought is not found in the local cache file,
/domain.txt.
>> Example: domain trace on
_________________________________________________________________
domain translate [on|off] Default: on
_________________________________________________________________
Display or set the domain translate mode. When set to 'on',
hosts are displayed as names. This is the more useful setting
(but unfortunately some versions of NOS are broken, so that even
if translate is set to 'on', no translation takes place).
When set to 'off', hosts are displayed as IP addresses.
>> Example: domain translate off
_________________________________________________________________
domain verbose [on|off] Default: off
_________________________________________________________________
Display or set the domain verbose mode. When set to 'off', only
the host name is displayed, without the domain suffix. This is
the more useful setting.
When set to 'on', the full host name with suffix is displayed.
>> Example: domain verbose on
_________________________________________________________________
domain xyzzy
_________________________________________________________________
This is a magic word to enable domain queries to outside domain
servers when reading commands from the startup file. This should
only be used by those who have reliable access to a domain name
system server.