Site-to-Site VPN General Question

Hi,

I have a site-to-site VPN setup from a network in Azure to AWS.

For some reason and I'm not entirely sure why, but it doesn't let me communicate end-to-end if the below settings configured on the Site-To-Site VPN Connection are set to anything but:

Local IPv4 network CIDR: 0.0.0.0/0

Remote IPv4 network CIDR 0.0.0.0/0

Perhaps it's my misunderstanding but surely you should set this to the specific networks on each side, for example and using just generic 10 network IP's for arguments sake:

Local IPV4 network CIDR:

10.20.1.0/24 - Let's assume this is the subnet configured on AWS

Remote IPV4 network CIDR:

10.230.1.0/24 - Let's assume this is the subnet configured in the vnet on Azure side.

Surely this would allow traffic from 10.20.1.2/32 (let's say this is an EC2 instance)

to communicate end to with a Windows server at the other end IP:

10.230.1.5/32

Am I misunderstanding this or is there something I've missed, happy to discuss with anyone, I don't see it as an issue but it's bugging me it doesn't work the way I expect it to, Id rather have everything as restricted as possible rather than 0.0.0.0/0 but then again I suppose it is traversing over an IPSEC tunnel so it's not the end of the world..

Thanks in advance for any help,

Zack