Dual-WAN Configurations
The SR-series router is a Dual-WAN device, meaning it has two interfaces capable of providing Internet access by default -- its WAN Ethernet port and the plug-in cellular modem -- though additional LAN ports may even be reconfigured for supplemental Internet access. Active WAN connections can provide both failover and load balancing per user-defined parameters
Failover
By default, this allows the plug-in modem to serve as a secondary (backup) WAN that becomes the active connection once the Ethernet WAN port is detected as offline. The router then monitors the offline connection to see when it comes back online, which prompts the backup interface to once again become inactive.
Each interface has a Metric value associated with its IPv4 configuration. The example on the left of this page is associated with the WAN interface, which will take priority over all other interfaces by default (as seen by its Metric value of "1").
Connectivity Monitoring
Both tests are set via the default group config in Accelerated View -- it is not built into the firmware.
Devices that have not synced with AView will not have these tests enabled by default.
To properly trigger a failover (or failback) scenario, test parameters must be defined to monitor the primary connection. Both a Ping and HTTP test come built into the SR's WAN port configuration by default. After 4 failed attempts, the secondary connection will take over Internet access for the router. Similarly, the monitoring tests trigger the restoration of the primary WAN connection when they detect that the interface with a higher metric has come back up. Note: 2 different tests are recommended to prevent false positives
NOTE: Best practices dictate that redundant tests (with divergent failure conditions) will be the best way to ensure proper connectivity monitoring/active recovery. With only a single test type, false positives could be reported.
Carrier Smart Select™
If one of the SIM cards requires a custom or unique APN, you will need to add this APN into the router's config under the Modem > APN Option
By default, the SR-series' plug-in modem is setup for automatic SIM selection. Meaning, if the router is unable to connect with the SIM in slot 1, after a specified number of failures (5 by default) the SR will automatically switch to use the SIM in slot 2. For this setup, you will need two SIM cards enabled, provisioned, and installed in the plug-in modem's SIM slots. The two cards can be from the same carrier or from different carriers.
Load Balancing
Traffic can be balanced between the Ethernet and Cellular WAN interfaces. This feature, often referred to as "load balancing," uses an interface's Weight value -- this is defined under the IPv4 expandable menu. The interfaces being balanced must share the same Metric value.
It is important to note that the two SIM slots cannot be leveraged simultaneously for load balancing; the load must be shared between the cellular modem and the wireline Internet connection. The Weight of an interface establishes its proportional contribution relative to the weight of its complimentary interface.
For example, setting the Ethernet WAN to a weight of "20" and the Cellular WAN to a weight of "5" establishes a 4:1 ratio -- the Ethernet interface will handle 4x the amount of data with this configuration.