Following are some of the common seen reasons for this problem:

• A host left a Netscape open but not borwsing.
• A host with an application to the Internet left open, such
  as PCN (PointCast), PING, ftp...etc.
• A Win95 or NT host with an incorrect IP address or netmask setup
  (NetBUI broadcast packets will be sent to Prestige and cause Prestige to outcall.)
• A workstation with wrong domain name setup or wrong Domain Name
  Server IP address setup.
• A host with incorrect IP address or subnet setup.

It is very easy to capture which packet that actually trigger the outcall,
and then identify the problem:

• Go to SMT Menu 24.1
• Stop all the Internet Access application
• Clear all the counters and packet triggered the call field, and let the system sit still.
• When the call is triggerred by some unknown reason, then you can see which type
  of packet that trigger the call. If it is IP, then you can tell which station sends the packet.

Here's how to read the packet for IP

• First make sure the Type is IP.
• Check the protocol field ( bold in above example ):

0x01: ICMP
0x06: TCP
0x11: UDP

• Check which station trigger the outcall ( underline numbers in above example )
    

  CC F7 CB B4	204.247.203.180 is the IP address of the workstation that triggered the outcall. This is the source address in the packet
  CC D9 00 02	204.247.203.180 is the IP address of the workstation that triggered the outcall. This is the destination address in the packet.
  ( Note: you can use 'nslookup' in Unix to verify who 204.217.0.2 is! )

• If the protcol is TCP (6) or UDP ( 0x11), then check the port field ( mark with ^^^^ )
    

  04 1C	port 0x41c ( 1052 ), is the source port
  00 15	port 0x15 ( 21 ), is the destination port. Some common seen ports are: 0x15  ( 21 ):  FTP 0x17  ( 23 ):  Telnet 0x19  ( 25 ):  SMTP 0x35  ( 53 ):  Domain Name Server 0x4F  ( 79 ):  Finger 0x50  ( 80 ):  WWW Http 0x89  ( 137 ): NetBios Name Service 0x8A  ( 138 ): NetBios Datagram Service 0x8B  ( 139 ): NetBios Session Service 0xA1  ( 161 ): SNMP 0xA2  ( 162 ): SNMP Trap 0x202 ( 514 ): syslog

• For the above example, you can interpret as:
  
  Workstation 204.247.203.180 was trying to ftp to 204.217.0.2, 
  and that triggered the outcall.

NetBIOS-Filter

The following filters prevent, that a NetBIOS Call (Broadcast) on the network triggers a connection with the Internet.

Netbios WAN (Filter Set 1)

This Filter must be inserted in Menu 11.1 (Internet Access Setup)

• Without ZyNOS (Firmware <= Version 1.50)

* Enter the number of the NetBIOS Filter at this position

• With ZyNOS (Firmware > Version 2.20)

Troubleshooting Example

The Zyxel Prestige Router opens a connection every minute, but nobody is using the Prestige.
Verify which process or services triggers the call.

In the Menu 24.1 we find, that the workstation 192.168.136.10 triggers a SQL*NET call to the workstation 193.72.194.28.

In the Menu 24.1 we find, that the workstation 192.168.136.11 triggers a NetBIOS call to the workstation 193.72.194.134.