Salesforce IPv4 and IPv6 support

The IP addresses in a range must be either IPv4 or IPv6. In ranges, IPv4 addresses exist in the IPv4-mapped IPv6 address space ::ffff:0:0 to ::ffff:ffff:ffff, where ::ffff:0:0 is 0.0.0.0 and ::ffff:ffff:ffff is 255.255.255.255. A range can’t include IP addresses both inside and outside of the IPv4-mapped IPv6 address space. Ranges like 255.255.255.255 to ::1:0:0:0 or :: to ::1:0:0:0 aren’t allowed.

In addition to this, we also recommend allow listing the Salesforce Regional IP addresses applicable by region.
https://help.salesforce.com/articleView?id=000321501&type=1&mode=1

Salesforce supports multiple options to configure how your domain is served. Whether you serve content for your domain through Salesforce, Salesforce Content Delivery Network, or an external provider, we strongly recommend using HTTPS.
https://help.salesforce.com/articleView?id=sf.domain_mgmt_domain_config_options.htm&type=5