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2 MANUAL INSTALLATION
DMS-CTC-20111123-0002 v1.0
2.5.2 Configuring a Backup Mobile Connection
Dial-On-Demand
By enabling the Dial-on-Demand (DoD) function when setting up the PPP interface, the new 2G / 3G connection will
function as a backup connection:

The “doddelay” (DoD delay) timer is the amount of time the MediaAccess Gateway waits before triggering the mobile
connection.

After injecting the mobile connection interfaces in the routing table, you will also notice a trigger interface (for default
routes) appearing (with according metric) in the routing table. When the main WAN interface goes down and the mobile
connection establishes, this trigger interface will disappear.

As long the main WAN connection is down, traffic will go over the mobile connection (routes with the higher metrics).
When the main WAN connection comes up again, DoD will injecting the DNS and routes with lower metric of the main
WAN connection in the routing table. According to the routing principles this will cause traffic to go over the main WAN
connection again.

The “Idletime” timer is the amount of time the MediaAccess Gateway waits before removing the DNS and routes of the
mobile connection once no more traffic is detected on this connection. During this time-out, two identical routes will exist
in the routing table, yet with different metrics. The lowest metric will be used according to routing principles.
Procedure
To configure the backup connection, complete the following steps:
Step 1: To set up a PPP interface
Step 2: Enable NAT address translation for the new PPP interface
Step 3: Save your changes!
Step 1: To set up a PPP interface
Proceed as follows:
1 To add a PPP interface, execute the following command:
2 Configure this PPP interface with a higher metric than the main WAN connection and enable the DoD function. The
user name and password are used for CHAP / PAP authentication for a specific APN:
3 Configure the route to add to the routing table when this interface comes up:
After starting up your MediaAccess Gateway, it might take some time until the main WAN connection comes up.
If this parameter is put to 0 an immediate parallel 2G / 3G connection will start up and disconnect immediately
when the main WAN connection has come up.
If this parameter is set to 0 and there is very few traffic over the 3G connection, each time new traffic is detected
on the 3G connection, the MediaAccess Gateway will attempt to switch back to its prioritized main WAN
connection.
:ppp ifadd intf=3G-Backup
:ppp ifconfig intf=3G-Backup dest=mobile_usb user=dummy password=dummy demanddial=enabled
idletime=60 doddelay=30 dnsmetric=20
:ppp rtadd intf=3G-Backup dst=0.0.0.0 metric=30
Your PPP interface can only be configured if it is detached.