Operation Manual

Configuring ISDN Call Destinations 133
24. Check the IPX Message Filter .
When a problem occurs on a NetWare server (e.g. "Server out of
disk space") or when a client issues a message (e.g. "Send to all"),
the corresponding warning or message is sent to all clients that
are logged in to that server. Afterwards, so-called "IPX Broadcast
Message Waiting" packets are sent to these clients in 2 second
intervals, until this warning or message is confirmed by the
clients. This does not cause any problems within a LAN, but
when two LANs are connected over ISDN, the following situa-
tion may appear:
Clients log in to a server over ISDN and Watchdog Spoofing is
enabled on the local router. Watchdog packets that poll the status
of IPX clients are consequently confirmed on the router as long
as the clients connected over ISDN are registered to be logged in
to the server. If the user of such a client forgets to log out before
switching the PC off and leaving the office (a quite common
behaviour), the client is still registered to be logged in. Or, users
of clients connected over ISDN leave their desks for hours. In
both cases, IPX Broadcast Message Waiting packets cause the
ISDN line to stay up all the time because they are not confirmed
until the clients log in to the server the next day or the users
return to their desks.
Another method, entering "castoff", has been reported not to
work on Windows clients under certain conditions and has a
major disadvantage: no messages are sent to those clients at all.
Thus, the IPX Broadcast Message Waiting Filter enhances espe-
cially your LAN-LAN links in two ways:
Users at their clients will receive such messages/warnings. The
IPX Broadcast Message Filter starts counting the subsequent "IPX
Broadcast Message Waiting" packets issued over ISDN to clients
as soon as no data packets are concurrently transferred over such
an ISDN link and starts filtering after five of these packets have
passed (after ten seconds, if the default polling interval of 2
seconds is used). As soon as the Inactivity Timeout expires, the
ISDN link is cleared physically. If the ISDN line is set up again to
transmit data, this filter is reset and begins to count anew as
described above.
For Remote Node-LAN connections with NetWAYS/ISDN, the
situations described are very unlikely to cause such ISDN links
to stay up because of Disconnect Timeout and other mechanisms