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Why is my ISDN router making too many calls ?

Vigor 2600
Vigor 2800

If you are using a router on an ISDN (dialup) line, it is a 'dial on demand' device. It will make a call whenever something on the network tries to data to the Internet. The call will then be ended after your set period of inactivity. Once you install the router, and your PCs are all set up to assume a permanent internet connection, those PCs might start sending data out when you're not expecting it - not the PCs themselves, but installed software. As such, when you first install the router, keep an eye on things and watch for abnormal activity on the B1/B2 channels (e.g. the line being online when no-one is surfing or sending email.

Windows Netbios DNS lookups are the most common cause, but these are normally trapped by default filters on the Vigor. Other suspects are software which updates itself automatically (e.g. virus software) or sometimes downright spyware or trojans/viruses.

To locate the source of a rogue call, you should cease all Internet activity; make sure no-one is surfing and that no email servers (etc.) are running. Then wait until the router goes online (B1 or B2 LED lights up) for "no apparent reason". You can then examine the router menu called Diagnostic Tools -> Triggered Packet Header where the data packet which triggered the last call is always shown. Be sure that it's not a legitimate call which was last made. The decoded packet will tell you the IP address of the PC on your LAN which triggered the call and also the IP address of the destination (somewhere on the Internet, commonly a DNS server). You will also see some port numbers - these give an additional clue of the service type.

ISDN Call Trigger

If you are using only Broadband, but not setting it to 'Always-On' the above information is also available for your Broadband triggered connections.

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