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Appendix A: Difference between IP addresses and hostnames
There are 2 different types of INTERNET addresses, NAME addresses and
NUMERIC addresses. NAME addresses look like ENGLISH words (and indeed
they are ENGLISH words that refer to a given host). A NAME address looks
like "tolsun.oulu.fi" - and that particular address refers to the machine
named TOLSUN in Finland. It is a UNIQUE address because no other machine
in the world has its NAME address the same as "tolsun.oulu.fi". Anytime
you say "telnet tolsun.oulu.fi" - you would always connect to TOLSUN in
Finland. NUMERIC addresses refer to those addresses that are made up of
NUMBERS for example "128.214.5.6" is the NUMERIC address for TOLSUN. This
address is also UNIQUE in that no other machine in the world will be use
those NUMERIC numbers. The NUMERIC address is usually more reliable than
the NAME address because not all sites can recognize and translate the
NAME address into it's numeric counterpart. NUMERIC always seems to work
best, but use a NAME address when you can because it is easier to tell
what host you are connected to.
Every Unix machine has a file called "/etc/hosts" on it. This file
contains NAME and NUMERIC addresses. When you supply IRC with a NAME
address it will at first try to find it in /etc/hosts, and then (if it's
really smart), use the local Domain Name Server (DNS) to find the NUMERIC
address for the host you want to connect to. Thus if you plan to use NAME
addresses keep in mind that on SOME sites the entry for the TARGET machine
must be found in /etc/hosts or the NAME address will fail. A typical
entry in /etc/hosts looks like this:
130.253.1.15 orion.cair.du.edu orion.du.edu orion # BSD 4.3
This particular example is the Host ORION at the University of Denver.
Notice that on the far left is the NUMERIC Address for orion. The
next few ENGLISH words are the NAME addresses that can be used for orion,
"orion.cair.du.edu", "orion.du.edu", "orion". ALL of these NAME addresses
will return the NUMERIC address "130.253.1.15" which IRC will use to
connect to the TARGET UNIX. (when I say TARGET UNIX I am refering to the
UNIX you want to connect to for IRC). Any futher questions about
/etc/hosts should be directed to "man hosts".
Appendix B: Enabling Summon Messages
+-----------------------------------------------------------------------+
| E N A B L I N G / S U M M O N M E S S A G E S |
+-----------------------------------------------------------------------+
*NOTE* You must have ROOT or special access to the GROUP tty ('/dev')
to do this. If you want to allow users around the world to summon
users at your site to irc, then you should make sure that summon works.
The "IRCD" program needs access to the GROUP of '/dev'. This
directory is where user TTY's are stored (as UNIX treats each Terminal
as a FILE!) IRCD needs GROUP ACCESS to /dev so that users can be
SUMMONED to the program by others users that are *in* the program.
This allows people from other Universities around the world to SUMMON
your users to IRC so that they can chat with them. Berkeley, SUN, HP-UX
and most of the newer versions of UNIX check to see if a USER is
accepting MESSAGES via the GROUP access rights on their TTY listing
in the /dev directory. For example an entry in '/dev' looks like this:
(Unix Path on BSD 4.3 UNIX is: /dev/ttyp0)
crw------- 1 jtrim 20, 0 Apr 29 10:35 ttyp0
You will note that 'jtrim' OWNS this terminal and can READ/WRITE to this
terminal as well (which makes sense because I am ENTERING DATA and
RECEIVEING DATA back from the UNIX). I logged into this particular
UNIX on "April 29th" at "10:35am" and my TTY is "ttyp0". But further
of *note* is that I do not have my MESSAGES ON! (mesg n) -- This is
how my terminal would look with MESSAGES ON (mesg y):
crw--w---- 1 jtrim 20, 0 Apr 29 10:35 ttyp0
With my MESSAGES ON (mesg y) I can receive TALK(1) requests, use the
UNIX WRITE(1) command and other commands that allow users to talk
to one another. In IRC this would also allow me to get IRC /SUMMON
messages. To set up the "IRCD" program to work with /SUMMON type
the following: (using ROOT or an account that has access to '/dev').
% chgrp tty ircd
% chmod 6111 ircd
The above commands read: "Give IRCD access to GROUP tty (which is /dev)
and then when ANYONE runs the IRCD allow SETUID and SETGID priviliges
so that they can use the /SUMMON command.
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