Draytek Vigor2620 Series Quick Start Manual page 33

If the 4G / LTE internet connection will be used as the primary connection, set the
Active Mode to Always On
If the connection will be used as a backup internet connection to the DSL / Ethernet
connection, set the Active Mode to Failover
Click OK to save those changes.
Go to [WAN] > [Internet Access], set the Access Mode to 3G/4G LTE Modem (DHCP
Mode) and click the Details Page button:
On the Details Page for the LTE WAN interface, configure the settings for SIM1 &
SIM2, the SIM1 slot is used as the primary SIM, SIM2 is used as a backup if SIM1 is
unable to connect:
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