How to get AD User Groups for user in Asp.Net?

ArrayList groups = new ArrayList();
foreach (System.Security.Principal.IdentityReference group in System.Web.HttpContext.Current.Request.LogonUserIdentity.Groups)
    groups.Add(group.Translate(typeof(System.Security.Principal.NTAccount)));

DirectoryEntry dirEnt = new DirectoryEntry("LDAP://my_domain_controller");
DirectorySearcher srch = new DirectorySearcher(dirEnt);
srch.Filter = "(objectClass=Group)";
var results = srch.FindAll();