retrieve all the groups a user is memberOf from active directory?

Hi, Sorry if the top is not closely PHP related. But I need to accomplish it using PHP. I can query the attribute 'memberOf' of a user from the active directory server with no problem. The challenge I'm facing now is how to obtain all the groups a user is member of. In many cases, a user can be in many groups which could be nested. Say, user is a member of group B which is a member of group A. So user should be member of group A implicitly. But in active directory, user's account only has memberOf: CN=Group_B,OU=security groups,OU=Users,OU=Coll,DC=some,DC=edu I can then check if Group_B's LDAP entry has any 'memberOf' attribute, so on and so on. If user's LDAP entry has multiple 'memberOf' attributes, I have to check each one to see if each group has any parent groups. Anybody ever had to deal with such a kind of issue and would like to shed some light (better with some code samples) how it should be done effectively? Any ideas would be greatly appreciated. Thanks, Bing