Draytek Vigor2120 series User Manual page 263

Mutual Authentication
(PAP)
Assigned IP Start
After finishing all the settings here, please click OK to save the configuration.
The Mutual Authentication function is mainly used to
communicate with other routers or clients who need
bi-directional authentication in order to provide stronger
security, for example, Cisco routers. So you should enable
this function when your peer router requires mutual
authentication. You should further specify the Username
and Password of the mutual authentication peer.
The length of the name/password is limited to 23/19
characters.
Enter a start IP address for the dial-in PPP connection. You
should choose an IP address from the local private network.
For example, if the local private network is
192.168.1.0/255.255.255.0, you could choose
192.168.1.200 as the Start IP Address.
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Vigor2120 Series User's Guide