1. Citate: “By default everyone is given access to the Internet (or the appropriate services in WinGate) until restricted by policies”.
Is this because of NAT enabled, Proxies enabled and binded to internal interfaces and Guest user account enabled by default?
Is disabling Guest prevent users from accessing Internet until specially setting up for it and/or granting access? Or in case client computer has necessary settings (DG + DNS ips for NAT and Proxy address for Proxy) he wil be able to connect to the Internet even after Guest is disabled? (Everything else by default)
This is because the default policies grant access to everyone for NAT, and all proxies. So regardless of how a user connects, there have been no restrictions applied by default. You will need to edit policy to apply restrictions. We strongly recommend against disabling the Guest account, as some internal functions require it to be enabled. If you're using the Windows user database, you can disable Guest in the OS, but have it enabled in WinGate. If you don't want guest access to say a proxy, set rules to require authentication, or use groups and/or policy to specify who can use the system.
If you disable Guest, the access won't be granted to users which are using the Guest account for services. However this can have other undesired issues. You can prevent Guest account from using the WWW proxy (say) without having to disable the account. You need to make the policy not grant access to Guest.
2. How can we restrict users access to Internet connected by pure NAT connection method? Only by port filtering on firewall and websites ban?
You can also use the policies in the Extended Networking section. This allows you more control. Be aware however, that the connection is reported to WinGate after the first packet has been sent through. WinGate then evaluates the policy and decides if the connection can be allowed to live. If policy blocks the connection, the connection is terminated. This means there can be the odd packet sneak through.
3. Is it possible to use AD user database for authorizatuions, and somehow keep using PCs ip based restrictions too (like assumed users). I mean for the same users. E.g., domain user JSmith is allowed to have access to Internet, but only from his PC (192.168.0.11). How can this be done on Wingate?
You need to decide whether the users will authenticate, or be assumed. You can set up policy so that an authenticated user can only access from a certain IP, by setting their IP in the locations tab for the policy that applies only to that user. You would need to set up a policy for each user for this though, or at least for each user that you wish to control in this way.