Did you try the steps from Check Point 600/700 Appliances Administration Guide R77.20.80 p. 154 ?
To add an Active Directory domain:
1. In the Active Directory section, click New.
The Add new Domain window opens.
2. Enter this information:
• Domain - The domain name.
• IP address - The IP address of one of the domain controllers of your domain.
Note - 600 appliances only support IPv4 addresses. 700 appliances support both IPv4 and IPv6 servers.
• User name - The user must have administrator privileges to ease the configuration process and create a user based policy using the users defined in the Active Directory.
• Password - The user's password. You cannot use these characters when you enter a password or shared secret: { } [ ] ` ~ | ‘ " # + \
• User DN - Click Discover for automatic discovery of the DN of the object that represents that user or enter the user DN manually. For example: CN=John James,OU=RnD,OU=Germany,O=Europe,DC=Acme,DC=com
3. Select Use user groups from specific branch only if you want to use only part of the user database defined in the Active Directory. Enter the branch in the Branch full DN in the text field.
4. Click Apply.
When an Active Directory is defined, you can select it from the table and choose Edit or Delete when necessary.
When you edit, note that the Domain information is read-only and cannot be changed.
When you add a new Active Directory domain, you cannot create another object using an existing domain.
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