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Transparent failover to a dial-out connection
Any console server, once configured with a dial-out connection option (i.e. an internal or external V.90 or 3G modem) can be set up to offer failover. In this mode, in the event of a disruption to the main network connection, a dial-out connection will be set up and access will switched transparently to this network connection. Then when the main network connection is restored, access is switched back. With this service enabled:
- the console server continually pings nominated probe addresses over the main network connection
- in the event of ping failure the console server dilas out and sets up a dial-out ppp over the land line or cellular modem
- access is switched to failover network
- the console server then is only accessible over the failover OoB modem connection. By default only SSH access is enabled on this connection. However in firmware versions later than 3.0.1 HTTPS access is also enabled (as is SSH accees to the serial ports)
- the administrator can then SSH (or HTTPS) connect to the console server and diagnose/ rectify the problem
- in the event that the problem is rectified and the pings are successful, access switches back to the main network connection and the dial-out connection terminated
You set up transparent failover when configuring the Network 1 (eth0) connection in System: IP:
- Specify the Failover Interface to be used when a fault has been detected with Network 1 (eth0). This can be the Internal Modem (for IM42xx or ACM5003-M models) or the Dial Serial DB9 (if you are using an external serial modem on the Console port - which all console servers support) or the PC Card (if you have an IM4004-5 with a Zoom Modem PC Card inserted) or the Internal 3G modem (for ACM5004-G)
- Specify the Probe Addresses of two sites (the Primary and Secondary) that the console server is to ping to determine if Network 1 (eth0) is still operational
- To set up the dial out modem:
- select the System: Dial menu option and the port to be configured (Serial DB9 Port or Internal Modem Port)
- in the Serial Settings sub-menu select the Baud Rate and Flow Control that will communicate with the modem
- in the Dial-Out Settings (FailOver) sub-menu check Enable Dial-Out and enter the access details for the remote PPP server to be called
Refer faq 354 for details on configuring the internal 3G modem on the ACM5004-G
With this mode configured, in the event the main network Network 1 (eth0) becomes unavailable for any reason, a dialout connection to the remote PPP server will automatically be set up. If the PPP connection is to the enterprize you will be provided with secure SSH connection to the console server. If the dial PPP connection is to an ISP who allocates you a dynamic Public IP address (and most generally do) you will also need to configure a Dynamic DNS service (refer faq348) to be able to access the console server.
By default, console servers with V3.1.0 firmware and later support automatic failure-recovery. So the console server continually pings probe addresses whilst in original and failover states. The original state will automatically be set as a priority and reestablished following three successful pings of the probe addresses (over the during failover. The failover state will be removed once the original state has been re-established.
Note: For firmware pre V3.1.0 the advanced console server does not support automatic failure-recovery back to the original state prior to the failover. So to restore networking to a recovered state the following command then needs to be run:
rm -f /var/run/*-failed-over && config -r ipconfig
If required, you can run a custom bash script when the device fails over. It is possible to use this script to implement automatic failure recovery, depending on your network setup. The script to create is:
/etc/config/scripts/interface-failover-alert
Failover and automatic failure recovery also can be configured to work with secondary broadband connections. Refer faq 273
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