access active directory frm another network using c#

Active directory configure on the  different network and I want to access this active directory from another network ,how we can do this using c#.

Active directory is configured on the Network1 and we want to access this active directory from the ntework2

I have done the below code ant it is working fine with in the same network.

   public bool IsUserAuthenticated(string domain, string userName)        {            try            {                DirectorySearcher dssearch = new DirectorySearcher(domain);                dssearch.Filter = string.Format("(&(objectClass=user)(sAMAccountName={0}))", userName);                //LDAP://CN=TestRahul Bhatnagar,CN=Users,DC=krishnas,DC=com                SearchResult sresult = dssearch.FindOne();                if (sresult == null)                {                    return false;                }            }            catch (Exception ex)            {                return false;            }            return true;        }