$vpnName     = "connection mane"
$vpnUsername = "user"
$vpnPassword = "password `$ with escaped dollar sign"
$ip          = "10.10.10.51" # some site in vpn to test access to

$result = gwmi -query "SELECT * FROM Win32_PingStatus WHERE Address = '$ip'"
if ($result.StatusCode -eq 0) {
    Write-Host "$ip is up."
}
else{
    Write-Host "$ip is down."
    Write-Host "Disconnecting..."
    rasdial.exe $vpnName /DISCONNECT
    Write-Host "Connecting..."
    rasdial.exe $vpnName $vpnUsername $vpnPassword
}