Implementation of get_ntp_servers for IOS.

        Returns the NTP servers configuration as dictionary.
        The keys of the dictionary represent the IP Addresses of the servers.
        Inner dictionaries do not have yet any available keys.
        Example::
            {
                '192.168.0.1': {},
                '17.72.148.53': {},
                '37.187.56.220': {},
                '162.158.20.18': {}
            }

def get_ntp_servers(self):
        """Implementation of get_ntp_servers for IOS.

        Returns the NTP servers configuration as dictionary.
        The keys of the dictionary represent the IP Addresses of the servers.
        Inner dictionaries do not have yet any available keys.
        Example::
            {
                '192.168.0.1': {},
                '17.72.148.53': {},
                '37.187.56.220': {},
                '162.158.20.18': {}
            }
        """
        ntp_servers = {}
        command = "show run | include ntp server"
        output = self._send_command(command)

        for line in output.splitlines():
            split_line = line.split()
            if "vrf" == split_line[2]:
                ntp_servers[split_line[4]] = {}
            else:
                ntp_servers[split_line[2]] = {}

        return ntp_servers