Find who is connected to MS SQL.

Find usernames and IP of connections to Microsoft SQL

SELECT DB_NAME(database_id) as [DB]
    , login_name
    , nt_domain
    , nt_user_name
    , status
    , host_name
    , program_name
    , COUNT(*) AS [Connections]
FROM sys.dm_exec_sessions
WHERE database_id > 0 -- OR 4 for user DBs
GROUP BY database_id, login_name, status, host_name, program_name, nt_domain, nt_user_name;

Function for Powershell to test if TCP port answers

function Test-Port($hostname, $port)
{
    # This works no matter in which form we get $host - hostname or ip address
    try {
        $ip = [System.Net.Dns]::GetHostAddresses($hostname) | 
            select-object IPAddressToString -expandproperty  IPAddressToString
        if($ip.GetType().Name -eq "Object[]")
        {
            #If we have several ip's for that address, let's take first one
            $ip = $ip[0]
        }
    } catch {
        Write-Host "Possibly $hostname is wrong hostname or IP"
        return
    }
    $t = New-Object Net.Sockets.TcpClient
    # We use Try\Catch to remove exception info from console if we can't connect
    try
    {
        $t.Connect($ip,$port)
    } catch {}

    if($t.Connected)
    {
        $t.Close()
       $true
    }
    else
    {
     $false                              
    }

}