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Title: ISDN keeps on building connections

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ISDN keeps on building connections

Applicable to
S.u.S.E. version: 4.4.1
Kernel version: 2.0.29

Symptom:

The ISDN connection to the provider is configured as Dial-On-Demand, and it works.

During operation, a connection will be automatically generated from time to time, without user intervention.

Cause:

A daemon is using the network connection.

This can also be another computer in the local network, if the ISDN computer is being used as a gateway.

Solution:

First of all, please read When booting, ISDN builds a connection for no reason.

If this doesn't apply, then try testing which daemon wants to build the connection. A (trivial) possibility is to stop all daemons one after the other, until this activity no longer occurs, at which point the bad guy has been found.

Establishing which daemon is building the connection:

Start the command isdnctrl verbose 3.

The ISDN subsystem will then protocol in /var/log/messages why a connection was built each time it occurs.

Examples:

  1. Mar  7 16:48:55 Galois kernel: OPEN: 192.168.102.11 -> 192.168.200.2 TCP, port: 1163 -> 23
    
    Explanation: Here you see which computer (192.168.102.11, which in this case is not the ISDN computer) would like to build a connection to which target address.

    The port number (in this case 23) indicates that a telnet session initiated the connection.
    The port numbers are listed in /etc/services.

  2. Mar  7 17:01:10 Galois kernel: OPEN: 192.168.102.6 -> 192.168.200.9 TCP, port: 513 -> 1023
    
    Explanation: 513 = login

  3. Mar  7 16:57:40 Galois kernel: OPEN: 192.168.102.22 -> 192.168.200.11 TCP, port: 1364 -> 21
    
    Explanation: 21 = ftp

  4. Mar  7 17:19:00 Galois kernel: OPEN: 192.168.102.11 -> 192.168.200.2 UDP, port: 1212 -> 37
    
    Explanation: 37 = time (netdate was started)

  5. OPEN: 194.95.192.145 -> 194.95.192.254 TCP, port: 1242 -> 110
    
    Explanation: Netscape was started, and it regularly tries to obtain mail via POP3 (Port 110).

    Torsten Römer (dode@muenchen.org) writes:
    Then I changed the setting in Options | Mail & News Preferences from Check for Mail every xx Minutes to never. That solved the problem.

Other causes could be: Other experiences (and solutions) are welcome!

Recommendations (check list):

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See also:

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Keywords: ISDN, SENDMAIL, DIAL, CONNECTION

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Feedback welcome: Send Mail to kfr@suse.de (Please give the following subject: SDB-isdn_dial)

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SDB-isdn_dial, Copyright SuSE GmbH, Nuremberg, Germany - Version:
Impressum - Last generated: 24. Feb 1999 14:48:40 by maddin with sdb_gen 1.00.0