Answer by Gabriel Luci for Querying LDAP in C# to get list of computers

You're almost there. A few things:

1. Set the page size to 1000. AD won't give you any more than 1000 at a time, so if you set it to anything over that you'll only get 1000 (if DirectorySearcher doesn't get back what it considers a full page, it'll stop asking)
2. Add the attributes you want to read to the PropertiesToLoad collection. If you don't add anything, it'll give you every attribute with a value, which is a bunch of unnecessary data you won't use. You'll likely only want to see the cn attribute (Common Name).
3. Use FindAll() to get the results. Make sure you wrap this in a using statement to prevent memory leaks (the documentation says so).
4. When you look at the results, every property is presented as an array, whether it is or not in AD. So you'll need to use [0] in most cases. For future reference (not applicable here): if a property is not set in AD, it won't be in the Properties collection at all, so, for optional attributes, you'll have to use Properties.Contains() to see if it's there first.

Working from what you have, here is a method that will return a list of computer names:

public IEnumerable<string> ComputerList(){    DirectoryEntry rootDSE = new DirectoryEntry("LDAP://MyDomain.Local");    DirectorySearcher computerSercher = new DirectorySearcher(rootDSE)    {        PageSize = 1000,        Filter = "(&(objectClass=computer))"    };    computerSercher.PropertiesToLoad.Add("cn");    using (var results = computerSercher.FindAll())    {        foreach (SearchResult result in results)        {            yield return (string) result.Properties["cn"][0];        }    }}

Update: To answer your questions in your comment:

1. The yield basically tells it to "add this item to the collection that will be returned". There is a little more going on in the background, which you can read about here. But in simplest terms, it saves you from having to create your own list, add items to that list and return the list.
2. I changed the return type from string to IEnumerable<string> because you are getting multiple results from your search, so I assume you want to return all of those results. This method will give you a list of computer names, not just one computer name.
3. FindAll() returns a SearchResultCollection. For some reason I don't know, the objects returned from SearchResultCollection in a foreach are presented as object. So you need to cast them to SearchResult explicitly to use them.