If a connection to a WAN interface is lost for any reason, the Connect EZ 16/32 device will immediately fail over to the next WAN or WWAN interface, based on WAN priority. See Configure WAN/WWAN priority and default route metrics for more information about WAN priority.
Active vs. passive failure detection
There are two ways to detect WAN or WWAN failure: active detection and passive detection.
- Active detection uses Digi SureLink technology to send probe tests to a target host or to test the status of the interface. The WAN/WWAN is considered to be down if there are no responses for a configured amount of time. See Configure SureLink active recovery to detect WAN/WWAN failures for more information about active failure detection.
- Passive detection involves detecting the WAN going down by monitoring its link status by some means other than active detection. For example, if an Ethernet cable is disconnected
Default Digi SureLink configuration
Surelink is enabled by default for IPv4 on all WAN and WWAN interfaces, and is configured to perform two tests on these interfaces:
- Interface connectivity.
- DNS query to the DNS servers for interface's the network connection.
DNS servers are typically received as part of the interface's DHCP client connection, although you can manually configure the DNS servers that will be used by SureLink.
Note If your device is operating on a private APN or on wired network with firewall restrictions, ensure that the DNS servers on your private network allow DNS lookups for https://remotemanager.digi.com; otherwise, the SureLink DNS query test will fail and the Connect EZ 16/32 device will determine that the interface is down.
By default, these tests will be performed every 15 minutes, with a response timeout of 15 seconds. If the tests fail three consecutive times, the device will reset the network interface to attempt to recover the connection.
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