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Hot-Stanby Mode vs. Active-Standby Mode

Published On: May 25, 2016 

High Availability (HA) is a simple solution for business downtime caused by hardware failure. When HA is enabled, the network administrator can have a second router on the network to deliver full routing services during the downtime of the main router. Virtual IP is used for LAN clients' gateway IP, so there is no configuration change required when the backup router takes place.

DrayTek High Availability (HA) feature offers two modes, Hot-Standby and Active-Standby, this article explains the difference between them.

 Hot-Standby Mode

Primary and Secondary router share the same WAN source. Usually, only the Primary is online. When Primary goes down, Secondary comes up, dial up the same WAN line, and continue to provide Internet service to LAN clients. If there is a LAN does not set to have the hardware redundancy, it will not be able to access the internet after the primary router goes down.

an illustration of network topology with two routers

For the figure above,

  • LAN1 is the High Availability Management LAN
  • LAN2 and LAN3 are set to have the hardware redundancy. They will access the Internet through V2925_A normally. If V2925_A go down, these two LANs will access the internet through V2925_B.
  • LAN4 does not have the hardware redundancy. It will access the Internet through V2925_A only. If V2925_A goes down, this LAN lost Internet connection.

Active-Standby Mode

In the Active-Standby mode, the Primary and Secondary router connect to different WAN sources; also, the Secondary will always be online. The clients of the LAN which is configured to have the hardware redundancy (LAN2 and LAN3 in the following topology) will access the Internet through the primary router normally. When the primary router goes down, these clients will access the Internet through the secondary router. The clients of the LAN not having the hardware redundancy setup (LAN4 and LAN5 in the following topology) will access the Internet through the router which they connect to; when their router goes down, they lost Internet connection.

an illustration of network topology with two routers

For the figure above,

  • LAN1 is the High Availability Management LAN.
  • LAN2 and LAN3 are set to have the hardware redundancy, and they will access the internet through V2925_A normally. If the V2925_A goes down, they will access the internet through V2925_B.
  • LAN4 and LAN5 do not have the hardware redundancy, so they will access the internet through the router they connect to only. If the router they connect to goes down, these LANs lost the Internet connection.

Hot-Standby Mode

The primary and secondary router use the same public IP address for Internet Access. The secondary device will automatically synchronize the configurations from the primary router. In fact, the configuration of both routers cannot be different. The secondary router is always idle when the primary router is working. Only when the primary device is down or detecting no active switch port on LAN or WAN interface, will the secondary device will be up and take over the primary router's role.

an illustration of Vigor3900 HA in Hot-Standby Mode

Active-Standby mode

The primary and the secondary router use different public IP addresses for Internet Access. The secondary router has its configuration, which can be different from the primary router. Both routers will operate at the same time. However, when one of the routers fails, the other can take over the traffic.

an illustration of Vigor3900 HA in Active-Standby Mode

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