Telnet...

[Jonathan I. Kamens]

In article <22331 at watdragon.waterloo.edu>, sppao at dahlia.waterloo.edu
(Peter Pao) writes:
> I can telnet from "Writer.yorku.ca" to my machine.  Does anyone know why I
> couldn't telnet back from my machine to "Writer.yorku.ca" ?

  The problem is not the machine itself, but rather with the address you
are trying to use to connect to it.

  "Writer.yorku.ca" does not have an internet address assigned to it,
according to the Internet domain nameserver for the yorku.ca domain. 
Instead, the nameserver has a "Mail Exchange" (MX) record for that host.

  A Mail Exchange record in a nameserver is used by mailers to find out
which machine handles mail for the host in question -- the MX record
specifies another machine name which *does* have an internet address,
and the mailer then sends the mail to that address, assuming that it
will be correctly forwarded to the machine with the MX record.

  The fact that you can connect *from* writer.yorku.ca to another
machine implies that the machine writer.yorku.ca is on *some* network
between you and it; this means one of two things:

1. There is a special network, not accessible from the general Internet,
which connects dahlia.waterloo.edu to writer.yorku.edu.  Since this
network is not accessible from the Internet (i.e. is not part of the
general Internet), writer.yorku.ca doesn't have an Internet address.

2. Writer.yorku.ca IS connected to the Internet.  However, Either its
Internet address is registered under another name, or the address isn't
registered at all, so you would have to know the IP address yourself in
order to connect to it.

The best way to find out which of these is the case would be to ask
someone there, not to ask the entire world :-).  Possibly, if
writer.yorku.ca is running Unix, the file /etc/rc.conf, /etc/rc, or
/etc/rc.net will mention the network address somewhere in it, if the
machine is on the Internet.

Jonathan Kamens			              USnail:
MIT Project Athena				11 Ashford Terrace
jik at Athena.MIT.EDU				Allston, MA  02134
Office: 617-253-8495			      Home: 617-782-0710