LANCOM Support Knowledgebase Document No. 1903.1509.1533.RHOO - V1.10

Backing up an Internet connection with 3G or 4G


This document describes how to set up a redundant Internet connection by configuring a backup based on a UMTS/3G or LTE/4G connection.



A 3G/4G router from LANCOM is employed as the Internet gateway for a company network. The device is set up with a functioning Internet connection via ADSL, SDSL or VDSL.

To ensure that the Internet remains available in case the DSL Internet connection should fail, the LANCOM is set up with a second Internet connection via UMTS/3G or LTE/4G. This is configured to connect automatically if the DSL connection fails.

The 3G/4G connection remains inactive as long as the DSL connection is working, so saving any connection charges and preventing any maximum data transfer volumes from being exceeded.


1) Configuring the UMTS/3G or LTE/4G connection:

This example configuration is based on a LANCOM router with built-in 3G/4G modem (e.g. LANCOM 1781A-3G).

1.1) Launch the Setup Wizard in LANconfig and select the option Set up Internet access.

1.2) We create a new IPv4 connection.

1.3) In the following dialog, select the option Mobile interface (internal modem).

1.4) Set the Country where the 3G/4G modem is to be operated.

1.5) Select your Internet service provider from the list that follows.

1.6) Enter a name for the Internet connection and the dial-up number given to you by your provider.

Please only change the default value for the dial-up number if you have received a different value from your provider.

1.7) Enter your PIN for the 3G/4G connection. Should your provider have communicated a different APN, modify the default value to suit.

Depending on the provider's APN, your 3G/4G connection may be assigned a public IP address or a private IP address. Information on this is available from your provider.

1.8) In the following dialog, accept the default value for the short-hold time.

  • A short-hold time setting of 9999 causes the UMTS/3G or LTE/4G connection to remain connected permanently, and a disconnect will be automatically reconnected.
  • A short-hold time setting of 0 causes the UMTS/3G or LTE/4G connection to remain connected permanently, but a disconnect is not automatically reconnected.
  • If you want your 3G/4G connection to be disconnected when inactive, enter an appropriate value for the short-hold time (e.g. 300 seconds).

1.9) In the next dialog, select the option Leave the current default route, as the already configured DSL Internet connection is to remain the primary Internet connection.

1.10) Click on Finish to write the configuration back to the LANCOM router.

2) Setting up the back-up function:

2.1) Open you the LANCOM router's configuration and go to the menu Configuration -> Communication -> Call management -> Backup table.

2.2) Click on the Add... button to create a new entry.

2.3) Set the Remote site as the configured DSL Internet connection.

2.4) In the field Backup list, enter the 3G/4G connection (in this example: KPN). Now close the dialog windows with the OK button.

2.5) By default a backup connection will be established 20 seconds after failure of the main Internet connection. You can change the value, but we recommend that you do not enter a value of less than 10 seconds.


The failure of an Internet connection is detected when there is no response to the line polling. Line polling involves the regular transmission of ICMP packets to a public IP address. If the LANCOM router receives no response to its line polling , it assumes that the Internet connection has failed.

For Internet connections where the LANCOM router handles the authentication with the provider, then an entry is required in the PPP list with a value for the line polling, among other things. Check that line polling is configured for the DSL Internet connection.

For Internet connections managed by another upstream router, the connection between the LANCOM router and the upstream router must be configured as a DSL Internet connection via a plain Ethernet connection (IPoE) (also see Database 'SP Knowledgebase', View '03. Edit Documents\by Responsible, Status', Document 'Setting up Internet access via an IPoE (plain Ethernet) connection').

For this type of configuration, line polling for the DSL Internet connection must be configured subsequently.
  • Open the menu Configuration -> Communication -> Protocols -> Polling table and click on Add....
  • Set the Remote site as your DSL Internet connection.
  • In the field IP address 1 enter the public IP address of an Internet remote site (e.g. In the fields IP addresses 2 – 4 you can enter other public IP addresses.
  • In the fields Ping interval and Retries you can retain the default settings. The default settings are a ping interval of 20 seconds and 5 retries.

2.6) Write the configuration back to the LANCOM router. This concludes the configuration.

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