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InetDB/Resolver
This website contains an archive of files for the Acorn Electron, BBC Micro, Acorn Archimedes, Commodore 16 and Commodore 64 computers, which Dominic Ford has rescued from his private collection of floppy disks and cassettes.
Some of these files were originally commercial releases in the 1980s and 1990s, but they are now widely available online. I assume that copyright over them is no longer being asserted. If you own the copyright and would like files to be removed, please contact me.
| Tape/disk: | Home » Personal collection » Acorn hard disk » apps » web |
| Filename: | InetDB/Resolver |
| Read OK: | ✔ |
| File size: | 217D bytes |
| Load address: | 0000 |
| Exec address: | 0000 |
Duplicates
There is 1 duplicate copy of this file in the archive:
- Personal collection » Acorn ADFS disks » Greaseweazled » adfs_1.6M_NetBits.adf » InetDB/Resolver
- Personal collection » Acorn hard disk » apps » web » InetDB/Resolver
File contents
INetDB - Cacheing Resolver
--------------------------
Copyright (c) 1994 Adam Goodfellow
This software is in part based upon source that is
Copyright (c) 1985, 1988 Regents of the University of California.
All rights reserved.
[NOTE: The InetDB module itself is no longer required by ArcWeb. However,
the configuration files used by ArcWeb are the same as those required by
InetDB, thus the instructions are the same]
Introduction
============
The basic Acorn and FreeNet TCP/IP stacks allows names of hosts with which
you want to communicate to be kept in a local file to save you having to
remember the numeric IP address for each host. For small networks this is
generally quite acceptable.
However, for larger networks and especially the Internet, keeping the
hosts file upto date can be very time consuming, if not impossible.
To get round this problem, it is normal for one or more machines on a
network to provide host name and IP address databases that are
accessable on a single machine.
In actual fact, with very large networks, this database (Domain Name
System or DNS) is distributed amongst a number of machines (called
name-servers), each being responsible for pursuing information about
other networks (domains) on behalf of hosts on its local network (in its
local domain), and answering secific queries about its local network
(domain) from systems on other networks (in other domains).
The Resolver provided as part of the INetDB module performs the task of
communicating with nameservers on behalf of many applications written
for the FreeNet and/or Acorn TCP/IP stacks.
Normally, as the name-server is a machine connected to your local
network, the time taken to get a reply from a nameserver is quite short,
a fraction of a second on a lightly loaded network and a lightly loaded
name-server.
However with heavily loaded networks and nameservers, or if the query
has to be sent over serial connection via a modem to a nameserver on the
Internet, the time taken for the response can be quite long, especially
with the recent upsurge in Internet use. Also, in circumstances of heavy
network conjestion, additional queries caused by resending of requests
that have been deemed lost further degrades network performance.
The obvious solution is to somehow reduce the dependancy upon the
name-server for processing queries every time you make a connection to
another named host.
This what sets this resolver apart from the types of resolver commonly
found on desktop computers. It remembers information recently obtained
from a name-server in a cache and so is often able to give an instant
responce to a repeat of recent similar query, making it very appropriate
for use where the nameserver is at the other end of a dial up connection
via a modem.
The cacheing methods used are such that so long as the name-servers are
providing accurate information about the life time of data retrieved,
then the cache will only give upto date information, and will
automatically remove information considered out of date, ensuring a
fresh copy is read from the nameserver.
Setting Up
==========
Resolver configuration is stored in the file "!FreeUser.Files.ResConf".
Options in this file are as follows: (See example)
nameserver
----------
nameserver <ip_address>
Internet address (in dot notation) of a name server that the resolver
should query.
Up to MAXNS (currently 3) name servers may be listed, one per keyword.
If there are multiple servers, the resolver library queries them in the
order listed. If no nameserver entries are present, the default is to
use the name server on the local machine. (The algorithm used is to try
a name server, and if the query times out, try the next, until out of
name servers, then repeat trying all the name servers until a maximum
number of retries are made).
domain
------
Local domain name.
Most queries for names within this domain can use short names relative
to the local domain.
If no domain entry is present, the domain is determined from the local
host name returned by gethostname() the domain part is taken to be
everything after the first '.'.
Finally, if the host name does not contain a domain part, the root
domain is assumed.
search
------
Search list for host-name lookup.
The search list is normally determined from the local domain name; by
default, it begins with the local domain name, then successive parent
domains that have at least two components in their names. This may be
changed by listing the desired domain search path following the
\fIsearch\fP keyword with spaces or tabs separating the names.
Most resolver queries will be attempted using each component of the
search path in turn until a match is found.
Note that this process may be slow and will generate a lot of network
traffic if the servers for the listed domains are not local, and that
queries will time out if no server is available for one of the domains.
The search list is currently limited to six domains
with a total of 256 characters.
sortlist
--------
Sortlist allows addresses returned by gethostbyname to be sorted.
A sortlist is specified by IP address netmask pairs. The netmask is
optional and defaults to the natural netmask of the net. The IP address
and optional network pairs are seperated by slashes. Up to 10 pairs may
be specified.
e.g. sortlist 130.155.160.0/255.255.240.0 130.155.0.0
options
-------
Options allows certain internal resolver variables to be modified.
The syntax is
options <option> ...
where <option> is one of the following:
debug sets RES_DEBUG in _res.options.
ndots sets a threshold for the number of dots which must appear in a
name given to res_query (see resolver) before an initial
absolute query will be made. The default for n is 1, meaning
that if there are any dots in a name, the name will be tried
first as an absolute name before any search list elements are
appended to it.
cachesize
---------
Enables the RR cache. Values may be given as <n> bytes, or <n>k kbytes.
Size less than 1024 are rounded upto 1024.
cacheload
---------
Read RRs from one or more file into the cache. If you are saving the
cache at shutdown, then one of thes files should be the cache file.
for eg:
cacheload resboot rescache
cachesave
---------
This sets where the cache is saved to at shutdown.
retry
-----
This sets the number of retries attempted to each nameserver (default 4)
timeout
-------
This sets the min and max timeouts between retrying the same nameserver again.
After each retry, the timeout is doubled upto the max value.
Nameserver retries are dstributed through the timeout period, so if the
timeout period is 6 seconds, and 3 nameservers have be specified, the
next nameserver is tried 2 seconds after the first.
----
The domain and search keywords are mutually exclusive. If more than one
instance of these keywords is present, the last instance wins.
The search keyword of a system's resolv.conf file can be overridden on a
per-process basis by setting the environment variable LOCALDOMAIN to a
space-separated list of search domains.
The options keyword of a system's resolv.conf file can be amended on a
per-process basis by setting the environment variable RES_OPTIONS to a
space-separated list of resolver options as explained above under
options.
The keyword and value must appear on a single line, and the keyword
(e.g. nameserver) must start the line. The value follows the keyword,
separated by white space.
Programmer Interface
====================
This file is incomplete, there are also a few *commands, some of which
are implemented.
The SWI Interface is as follows:
SWI Internet_GetHostByName &46000
On entry:
R0 = 0
R1 = -> host name
On exit:
R1 = pointer to hostent structure or NULL if not found
SWI Internet_GetHostByAddr &46001
On entry:
R0 = 0
R1 = -> host addr
R2 = len of addr
R3 = type of addr
On exit:
R1 = pointer to hostent structure, or NULL if not found
Where the hostent stucture is defined as below. Note that all addresses
are given in net byte order (the reverse of the normal Acorn byte order).
struct hostent {
char *h_name; /* Official name of host */
char **h_aliases; /* Alternative names for host */
int h_addrtype; /* Host address type */
int h_length; /* Length of each address */
char **h_addr_list; /* List of addresses for host */
#define h_addr h_addr_list[0] /* Address, for back compatability */
};
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00000010 67 20 52 65 73 6f 6c 76 65 72 0a 2d 2d 2d 2d 2d |g Resolver.-----|
00000020 2d 2d 2d 2d 2d 2d 2d 2d 2d 2d 2d 2d 2d 2d 2d 2d |----------------|
00000030 2d 2d 2d 2d 2d 0a 0a 20 20 20 43 6f 70 79 72 69 |-----.. Copyri|
00000040 67 68 74 20 28 63 29 20 31 39 39 34 20 41 64 61 |ght (c) 1994 Ada|
00000050 6d 20 47 6f 6f 64 66 65 6c 6c 6f 77 0a 0a 54 68 |m Goodfellow..Th|
00000060 69 73 20 73 6f 66 74 77 61 72 65 20 69 73 20 69 |is software is i|
00000070 6e 20 70 61 72 74 20 62 61 73 65 64 20 75 70 6f |n part based upo|
00000080 6e 20 73 6f 75 72 63 65 20 74 68 61 74 20 69 73 |n source that is|
00000090 20 0a 20 0a 20 20 20 43 6f 70 79 72 69 67 68 74 | . . Copyright|
000000a0 20 28 63 29 20 31 39 38 35 2c 20 31 39 38 38 20 | (c) 1985, 1988 |
000000b0 52 65 67 65 6e 74 73 20 6f 66 20 74 68 65 20 55 |Regents of the U|
000000c0 6e 69 76 65 72 73 69 74 79 20 6f 66 20 43 61 6c |niversity of Cal|
000000d0 69 66 6f 72 6e 69 61 2e 0a 20 20 20 41 6c 6c 20 |ifornia.. All |
000000e0 72 69 67 68 74 73 20 72 65 73 65 72 76 65 64 2e |rights reserved.|
000000f0 0a 0a 0a 5b 4e 4f 54 45 3a 20 20 54 68 65 20 49 |...[NOTE: The I|
00000100 6e 65 74 44 42 20 6d 6f 64 75 6c 65 20 69 74 73 |netDB module its|
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00000160 72 63 57 65 62 20 61 72 65 20 74 68 65 20 73 61 |rcWeb are the sa|
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000001c0 6e 0a 3d 3d 3d 3d 3d 3d 3d 3d 3d 3d 3d 3d 0a 0a |n.============..|
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0000217d 
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