Search with logon name in AD

OK, GetObject isn't really appropriate for this. This requires quite a bit more code to work properly.

First, your code is hard-coding the directory path to "search", as your code doesn't really do any searching at all. It also hard-codes the IP to use. That's bad because if that server is down or the IP changes, your search is going to fail. Also, if the directory path changes at all, your code has to be changed to accommodate the changes in the directory.

That is easily solved with a simple method:

Function GetDefaultNamingContext() As String
    Dim rootDse As New DirectoryEntry("LDAP://rootDSE")

    Dim domainDn = rootDse.Properties("DefaultNamingContext").Value.ToString

    Return domainDn
End Function

Now, need a method to search for an AD User object by its samAccountName. That's quite a bit more complicated than a single line of code:

Function GetAdObjectForSamAccount(ByVal samAccountName As String)
    ' Validate we have something to search for.
    If [String].IsNullOrEmpty(samAccountName) Then
        Throw New ArgumentNullException(samAccountName)
    End If

    ' Get the directory context to search.
    Dim context As String = GetDefaultNamingContext()

    ' Setup a search for a samAccountName.
    ' First, point to the directory to search.
    Using directory As New DirectoryEntry($"LDAP://{context}")
        ' Create a Searcher to do the work for us.
        Using searcher As New DirectorySearcher(directory, $"samAccountName={samAccountName}")
            ' Search the entire subtree of the directory because
            ' Users can really be stored anywhere in a tree.
            searcher.SearchScope = SearchScope.Subtree

            ' This will store the result of the search
            Dim result As SearchResult

            ' This is going to be the DirectoryEntry object we
            ' return, if any.
            Dim returnObject As DirectoryEntry = Nothing

            ' Search the diroectory for the object we want.
            result = searcher.FindOne

            ' Check if an object result was found.
            If result IsNot Nothing Then
                ' Grab the DirectoryEntry object for the found object.
                returnObject = result.GetDirectoryEntry
            End If

            ' Return whatever we found back to the caller.
            Return returnObject
        End Using
    End Using
End Function

Why do this? Because you can call this method from others that all might work with a User object somehow, but in different ways. Each of those methods can use this method to grab a User object for them just based on the samAccountName.

For example, a method to return the DisplayName for a particular samAccountName, or what you're calling the "logon name".

Function GetDisplayNameForSamAccount(ByVal samAccountName As String) As String
    ' Validate we have something to search for.
    If [String].IsNullOrEmpty(samAccountName) Then
        Throw New ArgumentNullException(samAccountName)
    End If

    Dim displayName As String = String.Empty
    Dim adObject As DirectoryEntry = GetAdObjectForSamAccount(samAccountName)

    If adObject IsNot Nothing Then
        displayName = adObject.Properties("DisplayName")(0).ToString
    End If

    Return displayName
End Function

And to call this and get the full name you're looking for is really easy:

Dim name As String = GetDisplayNameForSamAccount("BCNF0167")

Console.WriteLine($"DisplayName = {name}")