Updated
Apr 13th, 2012
First Posted
Apr 13th, 2012

ET/BWMGR Failover System

Emerging Technologies bandwidth management appliances can be equipped with the optional but highly recommended hardware "failover" module. The Failover System is a must-have for any critical network segment, as it allows for a nearly seamless transition to the bypass state, allowing traffic to pass unrestricted when a failure condition occurs, or the system is taken down for maintenance or rebooted during an upgrade.
Conditions that trigger the Bypass State
• Loss of power • Hardware failure (power supply, HDD, MB) • Software crashes or panics • Administrator elects to bypass the unit

How does it work?

The 2-port Failover System has two states - Closed (Bypass State), and Open. When the appliance is powered down, the card is in Bypass mode, which means the two ports are "closed", and the two ports are physically connected through a series of relays. In this state, the two ports act as a passive coupler. The diagram above illustrates the setup of the appliance when configured with the failover option. As shown, this 2-port failover card is set up as a bridge, which functions like a 2-port switch. One port is connected to the outside / upstream connection (Internet), and the other port is connected to the inside network, usually a switch. Also plugged into the same inside switch is the management interface, which is typically an on-board ethernet port that is not involved in bridging or bandwidth management. When the appliance is powered on, the Failover card will remain in the Closed state until the bridge is configured and the ET/BWMGR has started. Once the appliance is able to pass and manage traffic, the bypassd daemon is started, which opens the relays, allowing the OS access to the individual ports, and then initializes the Watchdog Timer (WDT). The bypassd daemon then is responsible for "touching" the WDT on the Failover card. If the system goes down, the daemon will cease communication with the WDT. Within seconds (immediately if power is lost,) the Failover System will respond by enabling Bypass mode, allowing traffic to flow on your network as if the bandwidth management appliance wasn't there.

Why a third port?

Some might ask why the additional management port is necessary. The answer is that it's not strictly required, but allows for much more efficient bridging of traffic at higher throughputs vs. having an address on the bridge, and also enables the administrator to put the appliance into bypass mode while still being able to access the GUI and CLI remotely. This also gives the administrator the ability to take an appliance out of bypass mode in the unlikely event that a "false failover" occurs. For these reasons, a 3-port setup is the default on all ET/BWMGR Hardware Appliances sold with the Failover option.

How much traffic can the Failover pass?

The ET/Failover series cards are available to manage up to 10Gb/s of traffic. The ET/GigFailover and ET/GigFailover 82575 cards support 10/100/1000 Mb/s modes via RJ45 connectors, while the ET/10GigFailover supports 10000Mb/s modes with either RJ45 or CX4 connector, depending on which version you order. Also available are a 4-port 10/100/1000Mb/s failover cards, which have two pairs of linked ports - during bypass, ports 0 and 1 are coupled, and ports 2 and 3 are also coupled as a separate link. This allows for independent bridging for multiple egress paths or bonded links.

Failover Hardware from Emerging Technologies

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