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Old 06-23-2005, 11:00 AM   #1
LQ Newbie
Registered: Jun 2005
Posts: 26

Rep: Reputation: 15
Angry dport 113


I have three PCs:A,B,C.

PC A: OS:red hat 7.3 (IP: SERVER:telnetd,ftpd
PC B: OS:red hat 9.0 (IP: SERVER:telnetd,ftpd
PC C: OS:Windows 2000 (IP:; installed software: firewall

from C telnet A, firewall on C display:
Code: attempt connect to localhost's port 113 [Auther Idnet]
           TCP flagS
           deny connect!
from C telnet B, firewall on C no messages about "deny"

PC B and C's configure file about telnetd be same. look:
$ more /etc/xinetd.d/telnet
# default: on
# description: The telnet server serves telnet sessions; it uses \
#       unencrypted username/password pairs for authentication.
service telnet
        disable = no
        flags           = REUSE
        socket_type     = stream
        wait            = no
        user            = root
        server          = /usr/sbin/in.telnetd
        log_on_failure  += USERID
On PC A,B,C , run "netstat -an", I am not find "port 113"
On PC A, run `cat /proc/net/ip_conntrack |grep "port=113"`,display:
 tcp      6 114 SYN_SENT src= dst= sport=36915 dport=113 [UNREPLIED] 

src= dst= sport=113 dport=36915 use=1
My question:

Why PC A send tcp data to PC C's port 113 ?
How disable?
Old 06-23-2005, 02:07 PM   #2
Registered: Apr 2001
Location: Bremen, Germany
Distribution: Debian
Posts: 303

Rep: Reputation: 30
Originally posted by yoursmile

My question:

Why PC A send tcp data to PC C's port 113 ?
How disable?
Presumably the default authmode was changed in the two telnetd implematations and the box that triggers the ident request on port 113 is run with -a [valid|user] whereas the other box is not. This is nothing to worry about though. What is worrying is that you use telnet at all. Switch to ssh!!
Old 06-23-2005, 09:58 PM   #3
LQ Newbie
Registered: Jun 2005
Posts: 26

Original Poster
Rep: Reputation: 15
demian , thank you for your reply!

On PC A, according to "man telnetd" , display:
"Note that this option is only use ful if telnetd has been compiled with support for authentication, which is not available in the current version."

# /usr/sbin/in.telnetd --help
/usr/sbin/in.telnetd: invalid option -- -
Usage: telnetd [-debug] [-D (options|report|exercise|netdata|ptydata)]   
    [-h] [-L login_program] [-n] [port]
So I think telnetd's authmode is close.

Last edited by yoursmile; 06-23-2005 at 10:02 PM.


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