If you use a dedicated gateway, you can specify either an IP address that belongs to the same subnet where the gateway is deployed, or the private address of a local data center connected to the gateway through Direct Connect.

Unsupported network segments:

0.0.0.0/8
10.0.0.0/8
100.125.0.0/16
127.0.0.0/8
169.254.0.0/16
172.16.0.0/12
192.0.0.0/24
192.0.2.0/24
192.88.99.0/24
192.168.0.0/16
198.18.0.0/15
198.51.100.0/24
203.0.113.0/24
224.0.0.0/4
240.0.0.0/4
255.255.255.255/32

Can I Specify the Backend Address as a Subnet IP Address?