从搜索中排除域控制器

Question

我正在尝试列出用户是Active Directory中成员的组。该程序工作正常，但是，我需要确保该程序从其搜索中排除某些DC服务器（特别是备份DC）。如果有帮助，备份DC都以字母INT开头。

这是我的代码中的相对剪辑 -

using System.DirectoryServices.AccountManagement;
using System.DirectoryServices.ActiveDirectory;
...

    public List<GroupPrincipal> GetGroups(string userName)
    {
        List<GroupPrincipal> result = new List<GroupPrincipal>();

        UserPrincipal user = null;
        try
        {
            user = UserPrincipal.FindByIdentity(ctx, userName);
        }
        catch 
        {
            System.Windows.Forms.MessageBox.Show("Invalid User");
        }

        if (user != null)
        {
            //---need to exclude a subset of Domain Controllers from the---
            //---following search---
            PrincipalSearchResult<Principal> groups = user.GetGroups();

            foreach (Principal p in groups)
            {
                if (ckbissecuritygroup.Checked == true) {
                    if (p is GroupPrincipal)
                    {
                        GroupPrincipal gp = (p as GroupPrincipal);
                        if (gp.IsSecurityGroup == true)
                        {
                            result.Add((GroupPrincipal)p);
                        }
                    }
                }
                else
                {
                    if (p is GroupPrincipal)
                    {
                        result.Add((GroupPrincipal)p);
                    }
                }
            }
            return result.OrderBy(x => x.Name).ToList();
        }
        else
        {
            System.Windows.Forms.MessageBox.Show("Invalid User: " + userName);
            return result;
        }
    }

我对C＃很新，所以我希望这相对容易。有什么想法吗？