Telnet connection closes immediately upon connecting

[Kristoffer Knigga]

Hello all,

I have a legacy application that I have running on a couple of RHEL AS
4.5 servers that requires telnet connections. We are currently in the
process of fixing this requirement, but I digress. This weekend we
rolled out a new server with this application and soon after users
started hitting it this morning telnetd started dropping new connections
as soon as they were made. By all accounts, existing telnet sessions
and ssh were unaffected.

Example:
$ telnet localhost
Trying 127.0.0.1...
Connected to localhost.localdomain (127.0.0.1).
Escape character is '^]'.
Connection closed by foreign host.

This can be fixed by simply restarting xinetd, but it's kind of
annoying. I haven't been able to find a pattern yet as to what triggers
this, either. I've checked iptables and tcp wrappers, but neither
looked to be the culprit. /var/log/messages looks clean, too.

Any thoughts on either how to resolve this or get more information?

Kris


____________________________________________
Kristoffer Knigga
Systems Administrator
Arrow Financial Services
***@arrow-financial.com
847-324-7962

[m***@rcn.com]

Date: Mon, 15 Oct 2007 15:14:13 -0500
Subject: Telnet connection closes immediately upon connecting

<snip>
weekend we

rolled out a new server with this application and soon after users
started hitting it this morning telnetd started dropping new connections
as soon as they were made. By all accounts, existing telnet sessions
and ssh were unaffected.
$ telnet localhost
Trying 127.0.0.1...
Connected to localhost.localdomain (127.0.0.1).
Escape character is '^]'.
Connection closed by foreign host.

<snip>
Looks to me as though someone has shut down or firewalled telnet, to block new incoming connections. I'd want to look at the logs on the host, both messages and secure.

mark

[Geofrey Rainey]

I've seen this exact result too from a transparent proxy sitting in the
way - though
The output looked as though the TCP packets were reaching the server, it
was the
Transparent proxy doing it.


-----Original Message-----
From: redhat-list-***@redhat.com
[mailto:redhat-list-***@redhat.com] On Behalf Of Gaddis, Jeremy L.
Sent: Tuesday, 16 October 2007 9:53 a.m.
To: General Red Hat Linux discussion list
Subject: Re: Telnet connection closes immediately upon connecting

Post by m***@rcn.com
Looks to me as though someone has shut down or firewalled telnet, to

block new incoming connections. I'd want to look at the logs on the
host, both messages and secure.

If that were the case, the server would never respond to the initial
SYN, preventing the connection from ever being established.

I'd look a bit more closely at my TCP wrappers configuration,
Kristoffer. This is exactly the result you'll see if TCP wrappers is
preventing the connection.

--
Jeremy L. Gaddis
http://www.jeremygaddis.com/

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[Gaddis, Jeremy L.]

Post by Geofrey Rainey
I've seen this exact result too from a transparent proxy sitting in the
way - though
The output looked as though the TCP packets were reaching the server, it
was the
Transparent proxy doing it.

tcpdump to the rescue! =)

[Kristoffer Knigga]

From: Geofrey Rainey
Sent: Monday, October 15, 2007 3:58 PM
I've seen this exact result too from a transparent proxy sitting in the
way - though The output looked as though the TCP packets were reaching
the server, it was the Transparent proxy doing it.


Why would it pass connections at first, and then stop? And why would
restarting xinetd fix it?


From: Gaddis, Jeremy L.
Sent: Monday, October 15, 2007 3:53 PM
I'd look a bit more closely at my TCP wrappers configuration,
Kristoffer. This is exactly the result you'll see if TCP wrappers is
preventing the connection.


Both hosts.allow and hosts.deny are blank. I will try explicitly
allowing our network and see if that works.


From: Allen, Jack
Sent: Monday, October 15, 2007 3:49 PM
Add "instances = unlimited" or what ever number you want to limit the
number of telnet connections to in the /etc/xinetd.d/telnet file. I
forget what the default limit is.


I'll give this a shot, too.


Thank you all for the suggestions.

Kris

[Geofrey Rainey]

Just to clarify, this was on port 80 - a web proxy, and it wasn't
immediately closing the connection. The output from the proxy led me to
believe that the packets were reaching the web server when they weren't,
so it was rather confusing when I wasn't seeing any TCP connection on
the server (xinetd is not relevant in this case).

-----Original Message-----
From: redhat-list-***@redhat.com
[mailto:redhat-list-***@redhat.com] On Behalf Of Kristoffer Knigga
Sent: Tuesday, 16 October 2007 10:08 a.m.
To: General Red Hat Linux discussion list
Subject: RE: Telnet connection closes immediately upon connecting

From: Geofrey Rainey
Sent: Monday, October 15, 2007 3:58 PM
I've seen this exact result too from a transparent proxy sitting in the
way - though The output looked as though the TCP packets were reaching
the server, it was the Transparent proxy doing it.


Why would it pass connections at first, and then stop? And why would
restarting xinetd fix it?


From: Gaddis, Jeremy L.
Sent: Monday, October 15, 2007 3:53 PM
I'd look a bit more closely at my TCP wrappers configuration,
Kristoffer. This is exactly the result you'll see if TCP wrappers is
preventing the connection.


Both hosts.allow and hosts.deny are blank. I will try explicitly
allowing our network and see if that works.


From: Allen, Jack
Sent: Monday, October 15, 2007 3:49 PM
Add "instances = unlimited" or what ever number you want to limit the
number of telnet connections to in the /etc/xinetd.d/telnet file. I
forget what the default limit is.


I'll give this a shot, too.


Thank you all for the suggestions.

Kris

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[Kristoffer Knigga]

I just checked /var/log/secure (thanks, Mark) and noticed this:
xinetd[14216]: FAIL: telnet service_limit

What is the default limit on RHEL 4? I'm not expecting any more than
200 or so connections.

I guess I need to set that "instances = unlimited" option (thanks,
Jack).

Thank you all for your help!

Kris




-----Original Message-----
From: redhat-list-***@redhat.com
[mailto:redhat-list-***@redhat.com] On Behalf Of ***@rcn.com
Sent: Monday, October 15, 2007 3:44 PM
To: General Red Hat Linux discussion list
Subject: Re: Telnet connection closes immediately upon connecting

Date: Mon, 15 Oct 2007 15:14:13 -0500
Subject: Telnet connection closes immediately upon connecting

<snip>
weekend we

rolled out a new server with this application and soon after users
started hitting it this morning telnetd started dropping new
connections as soon as they were made. By all accounts, existing
telnet sessions and ssh were unaffected.
$ telnet localhost
Trying 127.0.0.1...
Connected to localhost.localdomain (127.0.0.1).
Escape character is '^]'.
Connection closed by foreign host.

<snip>
Looks to me as though someone has shut down or firewalled telnet, to
block new incoming connections. I'd want to look at the logs on the
host, both messages and secure.

mark

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[Greg Wiggill]

Cant seem to find tape control tools tctl or mt on Red Hat 5 ?

Is there something different now ?

[Steve Phillips]

Post by Greg Wiggill
Cant seem to find tape control tools tctl or mt on Red Hat 5 ?
Is there something different now ?

[***@wibble etc]# man -k tape
rmt (8) - remote magtape protocol module
rmt (rpm) - Provides certain programs with access to
remote tape devices
smbtar (1) - shell script for backing up SMB/CIFS shares
directly to UNIX tape drives
st (4) - SCSI tape device
stapex (5) - systemtap examples

[Cameron Simpson]

On 18Oct2007 09:54, Greg Wiggill <***@pronto.com.au> wrote:
| Cant seem to find tape control tools tctl or mt on Red Hat 5 ?
| Is there something different now ?

The package is probably just not installed. Here:

[/u/cameron]finola*> rpm -qf $(which mt)
mt-st-0.9b-3.fc7

So try installing mt-st.

Dunno about tctl. There's a libtctl package.
--
Cameron Simpson <***@zip.com.au> DoD#743
http://www.cskk.ezoshosting.com/cs/

The four types of homicide:
1. Felonious 2. Accidental 3. Justifiable 4. Praiseworthy
- Ambrose Bierce (1842-1914)

Type 4 was expanded upon by Faulkner, who, writing the screenplay for Philip
Marlowe - Humphrey Bogart - commented thus: "Some murders could be listed in
the newspaper under Civic Improvements."

[Gaddis, Jeremy L.]

Post by m***@rcn.com
Looks to me as though someone has shut down or firewalled telnet, to block new incoming connections. I'd want to look at the logs on the host, both messages and secure.

If that were the case, the server would never respond to the initial
SYN, preventing the connection from ever being established.

I'd look a bit more closely at my TCP wrappers configuration,
Kristoffer. This is exactly the result you'll see if TCP wrappers is
preventing the connection.

[Allen, Jack]

Add "instances = unlimited" or what ever number you want to
limit the number of telnet connections to in the /etc/xinetd.d/telnet
file. I forget what the default limit is.

---
Jack Allen


-----Original Message-----
From: Kristoffer Knigga [mailto:***@arrow-financial.com]
Sent: Monday, October 15, 2007 4:14 PM
To: redhat-***@redhat.com
Cc: Andy Plamann; Corey Reichle
Subject: Telnet connection closes immediately upon connecting

Hello all,

I have a legacy application that I have running on a couple of RHEL AS
4.5 servers that requires telnet connections. We are currently in the
process of fixing this requirement, but I digress. This weekend we
rolled out a new server with this application and soon after users
started hitting it this morning telnetd started dropping new connections
as soon as they were made. By all accounts, existing telnet sessions
and ssh were unaffected.

Example:
$ telnet localhost
Trying 127.0.0.1...
Connected to localhost.localdomain (127.0.0.1).
Escape character is '^]'.
Connection closed by foreign host.

This can be fixed by simply restarting xinetd, but it's kind of
annoying. I haven't been able to find a pattern yet as to what triggers
this, either. I've checked iptables and tcp wrappers, but neither
looked to be the culprit. /var/log/messages looks clean, too.

Any thoughts on either how to resolve this or get more information?

Kris


____________________________________________
Kristoffer Knigga
Systems Administrator
Arrow Financial Services
***@arrow-financial.com
847-324-7962
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