Opengear appliances with a secondary network or cellular interface can be configured to use this interface as a failover connection. For all models, the Internal or external PSTN modem can be used for failover (PPP dial-up Internet or RAS account required).
In the event of a disruption to the primary network connection, the Opengear automatically activates the secondary connection to re-establish in- and outbound network access.
When failover is enabled, the Opengear detects failure by periodically sending ICMP ping requests out the primary network interface to a primary and optional secondary probe address. If all of these requests should fail, the primary connection is deemed to have failed. When the primary network connectivity is restored (i.e. the pings succeed again), the Opengear automatically fails forward to the primary connection to resume normal operation.
There are three operation modes:
Always Up Out-Of-Band Mode
This is the default mode when no failover scheme has been configured. Failover detection is disabled. Only inbound connections on the cellular interface are routed back out the cellular interface, to enable OOB access from remote networks (e.g. incoming SSH). Otherwise outbound network connections (e.g. VPN client tunnels, SNMP alerts) are established according to the main static routing table, regardless of network state.
Failover detection is enabled on the primary interface. The secondary interface remains in a down state with no network configuration. When failover is initiated, the secondary network interface is started and configured. If a default route is installed on the secondary interfaces, it takes precedence over the default route on the failed primary interface. Outbound network traffic (e.g. VPN client tunnels, SNMP alerts) are established or re-established out the secondary connection during failover.
The advantage of this mode is the secondary connection is completely inactive during normal operation which may be advantageous where the goal is to keep the interface off the Internet as much as possible, e.g. a cellular plan with expensive data rates and no carrier-grade NAT.
Dormant Failover Mode
This mode (introduced in firmware 3.10.x) combines Always Up and Failover mode. Failover detection is enabled, however the secondary interface is kept in a dormant up state, i.e. activated and configured but with no traffic being actively routed out it. Only inbound connections on the cellular interface are routed back out the cellular interface, to enable OOB access from remote networks (e.g. incoming SSH).
When failover is initiated, the default route of the secondary interface takes precedence over the failed primary interface. Outbound network traffic (e.g. VPN client tunnels, SNMP alerts) are established or re-established out the secondary connection during failover.
The advantage of this mode is the secondary connection is available for inbound out-of-band access during normal operation.
How to Setup Failover
First, configure the secondary connection and test connectivity in the default Always Up mode. For cellular failover, this is under System -> Dial -> Internal Cellular Modem. For Ethernet failover, this is under System -> IP -> Management LAN Interface. For dial-out, it’s under System -> Dial -> Internal Modem or Serial Console for external modems.
Check connectivity under Statistics -> Failover & Out-of-Band -> Connection Status, and confirm other functions (e.g. remote SSH) are working as expected.
If you haven’t already, configure the IP Settings of the primary connection by clicking System -> IP -> Network Interface.
Scroll down the Failover section and under a Primary Probe Address for failover detection by ping, and optional Secondary Probe Address. If you want Dormant Failover, check the box.
Scroll to the bottom and click Apply.
Finally, simulate a failover by disconnecting the primary network cable, or making the probe addresses unavailable in some other way.
A Note about F2C (IP Passthrough)
Failover in F2C (Failover To Cellular) IP Passthrough context is external, and performed by the downstream router. From firmware version 4.1.0 onwards, IP Passthrough mode may be combined with any of the internal failover modes described above.