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Increase the reliability and performance of your network

Reliability of network services will depend on both reliable network hardware as well as the Internet connections. DrayTek Multi-WAN routers offer both hardware redundancy as well as multiple internet connectivity options to provide maximum up-time. These features are High Availability, WAN Load Balance and Failover. In this article we will discuss each of these features.

High Availability

High Availability is required in mission critical network installations where network services cannot be interrupted due to a hardware failure. Organisations such as company headquarters, hospitals, utility companies, data centres etc. will benefit from High Availability as any outage will cause significant interruption and/or losses.


The High Availability Feature in DrayTek routers provide uninterrupted network access should a hardware failure occur. It does this by using Hardware redundancy to provide maximum up-time for critical installations.  Here a High Availability group is created consisting of the primary router and one or more secondary routers. If the primary router suffers a hardware failure, then the secondary backup router will come on-line and take over the network connections. Since the secondary router is synchronised to the primary router there will be minimal disruption to users and network operations including firewall protection, VPN connectivity, etc. Depending on the mode used, this can happen from a number of milliseconds to a number of seconds.

High Availability utilizes the Common Address Redundancy Protocol (CARP) which allows multiple hosts on the same local area network to share a set of IP addresses. Its primary purpose is to provide Failover redundancy, especially when used with firewalls and routers.  There are 2 modes: Hot Standby and Active Standby. In Hot Standby mode, a secondary router is connected but not active, whereas in Active Standby mode, the secondary routers are active and can take traffic for some of the LAN clients.

With DrayTek routers configured for High Availability, a common Virtual IP address is shared between all routers in the High Availability group. This virtual IP address is used by the all LAN clients in the network as the default gateway. The LAN clients do not have to be re-configured with a new default gateway should the primary router fails. So the LAN clients will only see a broadcast from the router to update the MAC address for the default gateway which is the virtual IP address. This results in minimum interruption for LAN clients.


With the latest firmware for the Vigor2960 and Vigor3900 only a single virtual IP address is required for High Availability and this simplifies the configuration of High Availability for these routers.


DrayTek routers supporting High Availability are shown below. These include the Vigor3900, Vigor2960, Vigor2860, Vigor2925, Vigor2952 and Vigor3220 routers.


More information is available in the application note:  What is High Availability?

Configuration examples are available in the following application notes:

WAN Load Balance

Network reliability can also be increased by using the WAN Load Balance feature of Dual WAN and Multi-WAN routers. There are a number of benefits of using WAN Load Balance, including:

  1. Reduced reliance on a single service provider
  2. Increased bandwidth capacity to the Internet
  3. Increased Internet speed using Session Based Load Balance
  4. Ability to use VPN Load Balance feature in supported routers

WAN Load Balance is supported over any combination of WAN connections. These can be ADSL, VDSL2, Ethernet WAN, Optic Fibre, 3G/4G via USB 3G/4G modem or LTE connection in the LTE routers.

When using WAN Load Balance, dual WAN and multi-WAN routers allow you to connect each WAN interface to a different service provider and maintain Internet connectivity.  For example you can subscribe to two different service providers, and if Internet connectivity through one service provider goes down, you can still have continuous Internet connectivity through the other service provider.

It does not matter that the data connection was through the WAN connection that failed since the session will be re-established through the other WAN connection.

Internet traffic is distributed over each WAN connection using one of two algorithms which are based by the line speed of each WAN Internet connection. There are two options for Load Balance Mode. These are:

  • “Auto Weight” where the router automatically determines the traffic distribution
  • “According to Line Speed” where the traffic distribution is determined by the pre-configured line speed setting for each WAN connection.


More details on the difference between “Auto Weight” and “According to Line Speed” Load Balance mode are available in the following application note:

An advantage of WAN Load Balance is that on a network with a large number of users, the Internet bandwidth is effectively increased since Internet traffic from each computer is sent over more than one WAN connection.

Session Based WAN Load Balance

For businesses requiring greater Internet speed, a new feature has been introduced recently in dual and Multi-WAN routers known as Session Based Load Balance. This feature provides WAN aggregation through session based Load Balance.

This feature is discussed in the Blog article: “How to double your Internet speed” which is available at:

The diagram below illustrates that Internet traffic from the LAN client is sent over both WAN 1 and WAN 2 through the Vigor router.




VPN Load Balance

A feature of using WAN Load Balance is the ability to enable VPN Load Balance in supported routers. Here a VPN tunnel to a remote site can be established over multiple WAN connections. This has the advantage of increased bandwidth over the combined VPN tunnel to the remote site as well has providing redundancy should a WAN connection fail. This also ensures that the VPN tunnel can keep running without interruption hence minimising interruption to business activities.

An application note covering VPN Load Balance between two Vigor routers is available at:

In addition a video that describes VPN Load Balance is available at:

WAN Failover

WAN failover is used where a business may have one or more primary WAN connections to the Internet and require minimal interruption to network services. This feature is available on single WAN, dual WAN or Multi-WAN routers.

A business with an Internet connection as the primary link may have a second WAN connection such as another ADSL line or a 3G/4G USB modem which they only want to come on-line when the primary connection goes down.  For example they may have a prepaid 4G modem with no ongoing costs attached to the router in standby mode. In case the primary WAN goes down, the router will be automatically triggered to bring up the backup connection. It can take up to 10 seconds for the backup link to come on-line so there will be a brief interruption during this process.  This is a little longer than when using WAN Load Balance mode where all WAN connections are active.

Even with single WAN routers such as the Vigor2760 and Vigor2120 you still have the option of WAN Failover to a 3G/4G USB modem.


On Multi-WAN routers you can select when you want the backup WAN to come on-line. The options are shown in the image below from the Vigor2860 router. The options are to failover when:

  • Any of the selected WANs are disconnected
  • All of the selected WANs are disconnected


More information on WAN Load Balance and failover is available in the application note:

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