telnet

[Rick Stevens]

Ted Potter wrote:
> On Tue, 2005-03-29 at 09:23, roland brouwers wrote:
[snip]
>>Now, as to why ME behaves differently, I suspect it has to do with the
>>terminal emulation in its telnet protocol.  One of the last things a
>>login does is set the prompt string and many systems will "eat" the
>>first prompt, just due to the way they set up the connections.  I'll bet
>>that it's not necessary for a "CTRL-C", but a simple "ENTER" would get
>>you the prompt.
>>
>>Can you fix it?  Probably not.

>>As I told you before "ENTER" doesn't work and it is getting worse. It is
>>like eating my network. More and more workstations, even XP are waiting
>>on telnet. If you wait long enough they continue. Some workstations that
>>hat this problem do not anymore. What is this, PACKMAN?

It's "PacMan" (no "k").  :-)

First, let's do some preliminary stuff.  Get on the Linux machine and do
some network probing.  Start out with "netstat -an | grep :23" to see
how many current telnet sessions you have running.  By default, you're
limited to 60 concurrent connetions.

Next, by default, the system will try to log the remote hostname.  If
your DNS isn't doing reverse lookups or you don't have the Windows
boxes' IP addresses and hostnames in the Linux server's /etc/hosts file,
the system will wait for DNS to time out before allowing the session to
continue.

Ok, how to fix?  Well, if you have more than 60 concurrent sessions, you
have to ask yourself if that's a legitimate use (60 telnet sessions is
a LOT, but it depends on your usage).  If you need more, you need to go
into /etc/xinetd.d and edit the "telnet" file.  If you need, say, 100
concurrent telnet sessions, add in a line that reads:

	instances             = 100

If you are having DNS issues, you can disable DNS-related things by
changing the line:

	log_on_failure        += USERID

to:

	log_on_failure        =

Also, add a line:

	log_on_success        -= HOST

If you started with the original /etc/xinetd.d/telnet file, it should
look sort of like this after all the editing:

# default: on
# description: The telnet server serves telnet sessions; it uses \
#       unencrypted username/password pairs for authentication.
service telnet
{
         disable = no
	instances       = 100
         flags           = REUSE
         socket_type     = stream
         wait            = no
         user            = root
         server          = /usr/sbin/in.telnetd
         log_on_failure  =
	log_on_success  -= HOST
}

Once you're done with editing the file, save it and execute:

	/etc/rc.d/init.d/xinetd restart

to make xinetd use the new data.
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- Rick Stevens, Senior Systems Engineer     rstevens at vitalstream.com -
- VitalStream, Inc.                       http://www.vitalstream.com -
-                                                                    -
-      On a scale of 1 to 10 I'd say...  oh, somewhere in there.     -
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