About failover management
During availability monitoring, the appliance considers the path to be unavailable after three consecutive unsuccessful pings, and then selects the backup path. Every application has a default and a prioritized set of backup paths. Should the default path be unavailable, the highest-priority backup is instantly used (and then consecutively lower ones, if needed). Operators can block certain types of applications when the primary path becomes unavailable, with a goal of reserving the remaining available bandwidth for more critical applications. As soon as the default path becomes available, traffic is routed back to it.
Fail-to-wire
All SteelHead models and in-path network interface cards support fail-to-wire (also known as bypass) mode. In the event of a failure or loss of power, the appliance goes into bypass mode and traffic passes through unaccelerated. Many in-path network interface cards (NICs) also support a fail-to-block mode. If there’s a failure or loss of power, the appliance LAN and WAN interfaces power down and stop bridging traffic. The default failure mode is fail-to-wire.
If there’s a serious problem with the appliance or it’s not powered on, it goes into bypass mode to prevent a single point of failure. If the appliance is in bypass mode, you are notified by:
• the Intercept/Bypass status light on the bypass card.
• the system health status appears as Critical the appliance Management Console.
• SNMP traps, if configured.
• system logs (syslogs) log the transition to bypass mode.
• email notifications, if configured.
When the fault is corrected, new connections are accelerated; however, connections made during the fault aren’t. Appliances include a kickoff feature, which resets those connections and enables them to be optimized. Generally, connections are short-lived and kickoff is not necessary.
Fail-to-block
In fail-to-block (also known as disconnect) mode, the appliance powers down its LAN and WAN interfaces and stop bridging traffic in the event of failure or power loss.
When this mode is enabled, a failed appliance blocks traffic along its path, forcing traffic to be rerouted onto other paths (where the other SteelHeads are deployed). This is only useful if the network has a routing or switching infrastructure that can automatically divert traffic off of the link once the failed SteelHead blocks it.
You can use this mode with connection-forwarding, the allow-failure command, and an additional SteelHead on another path to the WAN to achieve redundancy.
You set fail-to-block mode in the SteelHead CLI.