You can configure network location policies to control access to SharePoint Online based on IP addresses. If you enable this option, you can enter IP addresses as specific addresses or as Classless Inter-Domain Routing (CIDR) blocks.
Configuring IP restrictions for SharePoint Online will affect all the services that use Office 365 Groups and SharePoint Online sites (such as OneDrive for Business and Teams).
If you configure this option, you'll want to include all of your organization's public NAT IP addresses. If you fail to configure your organization's addresses, you will lock yourself out of SharePoint Online administration and will need to open a support ticket to resolve the issue.
In addition, configuring IP address restrictions will probably have significant impacts on external site sharing and mobile application use.