telnet/ftp NOT DNS problem

telnet/ftp NOT DNS problem

Post by Alex Heiphet » Wed, 27 Jan 1999 04:00:00



Problem:
I can't telnet or ftp to FreeBSD box although I can work out of it fine,
ping, traceroute, etc. The connection just hangs for a couple minutes,
then tells me "cannot telnet..."

When I run trafshow on the server, I do see request for telnet/ftp coming,
but inetd (which _is_ running) does not react. (conf files are OK,
telent and ftp are among allowed services).

I looked over archives, it seem some people had very similar problem
when reverse DNS lookup didn't work and FreeBSD couldn't lookup
client. It is not the case, I can't telnet from hosts that can be
nslookuped fine.

Another person had the same problem and was advised to set tcp_extensions
to "NO" in /etc/rc.conf It didn't help me :-(

In other words, i searched up and low and cose to the end of the rope.
Your help is greatly appreaciated.

Regards,
A.Heiphetz
P.S. FreeBSD -3.0 -RELEASE.
...I used to run 2.2.6 and didn't have this problem there :-)

 
 
 

1. Slow ftp-telnet connect, but NOT a dns problem

hello, who knows what changed from 1995 to the last
netkit versions ?
Problem: telnet and ftp connect with kernel versions 2.xxx
over a firewall.
There is a delay about 8 seconds until the login prompt.
The host tries to send two pakets which are blocked by the firewall.
I can only say, that old linux version (from 1995 - kernel around 1.1xx)
dont do it.
This is tcpdump of the two pakets, which get rejected by the firewall:
15:40:01.500000 0:40:5:38:cb:cd 0:40:5:34:b5:35 0800 60:
195.88.189.125.23 > 195.88.189.136.4664: . ack 31 win 16338 (DF) (ttl
63, id 997)
this are the two pakets
---------
15:40:04.430000 0:80:ad:83:51:5a 0:40:5:33:3c:e3 0800 60:
195.88.189.125.1173 > 195.88.189.136.113: S 3232699201:3232699201(0) win
16060 <mss 1460> (ttl 6
3, id 998)
15:40:10.430000 0:80:ad:83:51:5a 0:40:5:33:3c:e3 0800 60:
195.88.189.125.1173 > 195.88.189.136.113: S 3232699201:3232699201(0) win
16060 <mss 1460> (ttl 6
3, id 999)
-----------
15:40:11.480000 0:40:5:38:cb:cd 0:40:5:34:b5:35 0800 60:
195.88.189.125.23 > 195.88.189.136.4664: P 1:4(3) ack 31 win 16338 (DF)
(ttl 63, id 1000)
----------
the firewall rejects any packets from outside without ack set.
Old linux versions dont send these two pakets. I tried to look into
telnetd
and the telnetlib but did not find the meaning of this pakets.

Has anyone an idea why the host generates such pakets ?

kind regards
--
+------------------------+---------------------------+

+------------------------+---------------------------+
| RDE Network Systems    | phone: +49 611 95031-0    |
| ISP + PoP Wiesbaden    | fax:   +49 611 95031-555  |
| Kirchbornstrasse 2     | www1:  http://www.ipw.net |
| D-65191 Wiesb./Germany | www2:  http://www.rde.net |
+------------------------+---------------------------+

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