High Availability with More Than Two Physical WAN Uplinks
Although only two active uplinks are supported at a time on an active/primary MX, additional uplinks should be utilized for tertiary failover on the secondary MX. One or two additional uplinks may be utilized on the secondary MX, and will become active when all uplinks on the primary MX fail or when a hardware failure occurs on the primary MX. These additional uplinks connected to the secondary MX can be part of a different IP subnet than the uplinks on the primary MX.
If there is a problem with the routed HA configuration, there may be various symptoms that will affect the network, and it may not be obvious that the root cause is routed HA. This section outlines what issues with HA typically look like, as well as recommended troubleshooting steps.
The most common sign of a problem with routed HA is a dual active scenario where both the primary and spare MX report in the dashboard as being active. This can be observed in the dashboard under Security & SD-WAN > Monitor > Appliance status and by comparing the current state of each appliance.
This will occur if the primary MX is online and sending heartbeats that aren't seen by the spare, resulting in the spare thinking that the primary is down. If both the primary and spare are in the active state, this will cause various issues with the network, affecting DHCP, routing, VPN, etc.
If network issues are occurring that appear to be related to routed HA, the following troubleshooting steps should be taken to identify the root cause: