To reach the network the ZeroTier client A is in from other ZeroTier clients, add a route to the network via the ZeroTier client A's IP address on the ZeroTier network on the ZeroTier Central web page. ZeroTier clients will automatically get this route on their routing table which will allow them to reach the network.

For the devices on the network to reach back to the ZeroTier clients, the source IP address of the frames that the devices on the network receive must be of the ZeroTier client A's IP address on the network. To achieve this, do masquerading (NAT) on the interface that connects to the network.

Example configuration on /etc/config/firewall for OpenWrt:

config zone
	option name 'lan'
	option output 'ACCEPT'
	option forward 'ACCEPT'
	option masq '1'
	option input 'ACCEPT'
	option network 'lan_dhcp'