ZyXEL Communications Prestige 128 Plus User Manual page 194

Prestige 128+ ISDN Router
16-4
If the remote dial-in user is negotiating IP, verify that the IP
address is supplied correctly in Menu 13. Check that either the
remote dial-in user is supplying a valid IP address, or that the
Prestige is assigning a valid address from the IP pool.
If the remote dial-in user is negotiating IPX, verify that the IPX
network number is valid from the IPX pool (if it is being used).
Troubleshooting