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Title: ISDN keeps on building connections

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ISDN keeps on building connections

Symptom:

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

Cause:

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

Solution:

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:

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.

• Name server requests
• Samba (see below)
• Sendmail

Recommendations (check list):

• Make sure that the search order in /etc/host.conf starts with hosts, and then the name server:

  order hosts bind
  multi on
  

• Enter all employed IP addresses in /etc/hosts. In particular: the ISDN computer directly connected to yours, the name server, and your computer's IP address (if it isn't dynamically assigned).
• Don't start routed, instead use static routing.
• Another useful solution is the installation of a caching only name server. For further information see DNS-HOWTO, for example at
  • On the S.u.S.E. server http://www.suse.de/doku/howto/DNS-HOWTO.html.
  • Locally installed: file:/usr/doc/howto/html/DNS-HOWTO.html
• If Samba is installed, see ISDN und Samba

See also:

S.u.S.E. ISDN howto
When booting, ISDN builds a connection for no reason
ISDN and Samba

Keywords: ISDN, SENDMAIL, DIAL, CONNECTION

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

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