Subnet router failover
When using subnet routers in large networks, you may want to provide a failover subnet router (also called a HA subnet router or high-availability subnet router) to ensure users of your network can continue to access resources if one routing device goes offline.
Step 1: Set up multiple subnet routers
Follow our guide to configure subnet routers, exposing the same routes on the same network on 2+ devices. For example, to expose 10.0.0.0/24,10.1.0.0/24, you’ll want to run a command like this on 2+ devices.
sudo tailscale up --advertise-routes=10.0.0.0/24,10.1.0.0/24
You can configure as many subnet routers as you want to act as a failover.
Only matching advertised routes will be configured for failover. Route prefixes are not expanded for failover.
For example, if multiple subnet routers are configured with
--advertise-routes=10.0.0.0/24,10.0.100.0/24, both routes can be used
for failover, whereas one subnet router configured with
--advertise-routes=10.0.0.0/24,10.0.100.0/24 and another configured with
--advertise-routes=10.0.0.0/16 will not be used for failover.
Subnet routers can advertise matching but disparate routes and be used for failover for the matching routes, but in practice this is not recommended.
Step 2: Activate the subnet routers in the admin console
Open the Machines page of the admin console, locate your subnet router and using the 
menu at the end of the table, select Review subnet routes. This will open up the Subnet settings.
Click Enable on your routes so that Tailscale distributes the subnet routes to the rest of the nodes on your Tailscale network.
Step 3: Done!
Once you have 2+ subnet routers exposing the same route on the same network, the Tailscale control server will automatically manage the failover between the different routers. Currently, if a subnet router is disconnected from the control plane for more than 15 seconds, traffic will be routed to another subnet router.