TP-Link TL-MR3420 User Manual page 37

 MTU Size - The normal MTU (Maximum Transmission Unit) value for most Ethernet
networks is 1500 Bytes. It is not recommended that you change the default MTU Size
unless required by your ISP.
Primary/Secondary DNS - (Optional) Enter one or two DNS addresses in dotted-decimal

notation provided by your ISP.
3. If your ISP provides a PPPoE connection, select PPPoE/Russia PPPoE option. And you
should enter the following parameters (Figure 4-12):
User Name/Password - Enter the User Name and Password provided by your ISP. These

fields are case-sensitive.
Secondary Connection - It's available only for PPPoE Connection. If your ISP provides an

extra Connection type such as Dynamic/Static IP to connect to a local area network, then
you can check the radio button of Dynamic/Static IP to activate this secondary connection.
Disabled - The Secondary Connection is disabled by default, so there is PPPoE

connection only. This is recommended.
Dynamic IP - You can check this radio button to use Dynamic IP as the secondary

connection to connect to the local area network provided by ISP.
Static IP - You can check this radio button to use Static IP as the secondary

connection to connect to the local area network provided by ISP.
Connect on Demand - In this mode, the Internet connection can be terminated

automatically after a specified inactivity period (Max Idle Time) and be re-established
TL-MR3420
Figure 4-12 WAN - PPPoE
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3G/4G Wireless N Router User Guide