# Copyright (C) 2017 Canonical Ltd. # # Author: Ryan Harper # # This file is part of cloud-init. See LICENSE file for license information. import copy import functools import logging import socket import struct import six from cloudinit import util LOG = logging.getLogger(__name__) NETWORK_STATE_VERSION = 1 NETWORK_STATE_REQUIRED_KEYS = { 1: ['version', 'config', 'network_state'], } NETWORK_V2_KEY_FILTER = [ 'addresses', 'dhcp4', 'dhcp6', 'gateway4', 'gateway6', 'interfaces', 'match', 'mtu', 'nameservers', 'renderer', 'set-name', 'wakeonlan' ] NET_CONFIG_TO_V2 = { 'bond': {'bond-ad-select': 'ad-select', 'bond-arp-interval': 'arp-interval', 'bond-arp-ip-target': 'arp-ip-target', 'bond-arp-validate': 'arp-validate', 'bond-downdelay': 'down-delay', 'bond-fail-over-mac': 'fail-over-mac-policy', 'bond-lacp-rate': 'lacp-rate', 'bond-miimon': 'mii-monitor-interval', 'bond-min-links': 'min-links', 'bond-mode': 'mode', 'bond-num-grat-arp': 'gratuitious-arp', 'bond-primary': 'primary', 'bond-primary-reselect': 'primary-reselect-policy', 'bond-updelay': 'up-delay', 'bond-xmit-hash-policy': 'transmit-hash-policy'}, 'bridge': {'bridge_ageing': 'ageing-time', 'bridge_bridgeprio': 'priority', 'bridge_fd': 'forward-delay', 'bridge_gcint': None, 'bridge_hello': 'hello-time', 'bridge_maxage': 'max-age', 'bridge_maxwait': None, 'bridge_pathcost': 'path-cost', 'bridge_portprio': 'port-priority', 'bridge_stp': 'stp', 'bridge_waitport': None}} def parse_net_config_data(net_config, skip_broken=True): """Parses the config, returns NetworkState object :param net_config: curtin network config dict """ state = None version = net_config.get('version') config = net_config.get('config') if version == 2: # v2 does not have explicit 'config' key so we # pass the whole net-config as-is config = net_config if version and config: nsi = NetworkStateInterpreter(version=version, config=config) nsi.parse_config(skip_broken=skip_broken) state = nsi.get_network_state() return state def parse_net_config(path, skip_broken=True): """Parses a curtin network configuration file and return network state""" ns = None net_config = util.read_conf(path) if 'network' in net_config: ns = parse_net_config_data(net_config.get('network'), skip_broken=skip_broken) return ns def from_state_file(state_file): state = util.read_conf(state_file) nsi = NetworkStateInterpreter() nsi.load(state) return nsi def diff_keys(expected, actual): missing = set(expected) for key in actual: missing.discard(key) return missing class InvalidCommand(Exception): pass def ensure_command_keys(required_keys): def wrapper(func): @functools.wraps(func) def decorator(self, command, *args, **kwargs): if required_keys: missing_keys = diff_keys(required_keys, command) if missing_keys: raise InvalidCommand("Command missing %s of required" " keys %s" % (missing_keys, required_keys)) return func(self, command, *args, **kwargs) return decorator return wrapper class CommandHandlerMeta(type): """Metaclass that dynamically creates a 'command_handlers' attribute. This will scan the to-be-created class for methods that start with 'handle_' and on finding those will populate a class attribute mapping so that those methods can be quickly located and called. """ def __new__(cls, name, parents, dct): command_handlers = {} for attr_name, attr in dct.items(): if callable(attr) and attr_name.startswith('handle_'): handles_what = attr_name[len('handle_'):] if handles_what: command_handlers[handles_what] = attr dct['command_handlers'] = command_handlers return super(CommandHandlerMeta, cls).__new__(cls, name, parents, dct) class NetworkState(object): def __init__(self, network_state, version=NETWORK_STATE_VERSION): self._network_state = copy.deepcopy(network_state) self._version = version self.use_ipv6 = network_state.get('use_ipv6', False) @property def config(self): return self._network_state['config'] @property def version(self): return self._version def iter_routes(self, filter_func=None): for route in self._network_state.get('routes', []): if filter_func is not None: if filter_func(route): yield route else: yield route @property def dns_nameservers(self): try: return self._network_state['dns']['nameservers'] except KeyError: return [] @property def dns_searchdomains(self): try: return self._network_state['dns']['search'] except KeyError: return [] def iter_interfaces(self, filter_func=None): ifaces = self._network_state.get('interfaces', {}) for iface in six.itervalues(ifaces): if filter_func is None: yield iface else: if filter_func(iface): yield iface @six.add_metaclass(CommandHandlerMeta) class NetworkStateInterpreter(object): initial_network_state = { 'interfaces': {}, 'routes': [], 'dns': { 'nameservers': [], 'search': [], }, 'use_ipv6': False, 'config': None, } def __init__(self, version=NETWORK_STATE_VERSION, config=None): self._version = version self._config = config self._network_state = copy.deepcopy(self.initial_network_state) self._network_state['config'] = config self._parsed = False @property def network_state(self): return NetworkState(self._network_state, version=self._version) @property def use_ipv6(self): return self._network_state.get('use_ipv6') @use_ipv6.setter def use_ipv6(self, val): self._network_state.update({'use_ipv6': val}) def dump(self): state = { 'version': self._version, 'config': self._config, 'network_state': self._network_state, } return util.yaml_dumps(state) def load(self, state): if 'version' not in state: LOG.error('Invalid state, missing version field') raise ValueError('Invalid state, missing version field') required_keys = NETWORK_STATE_REQUIRED_KEYS[state['version']] missing_keys = diff_keys(required_keys, state) if missing_keys: msg = 'Invalid state, missing keys: %s' % (missing_keys) LOG.error(msg) raise ValueError(msg) # v1 - direct attr mapping, except version for key in [k for k in required_keys if k not in ['version']]: setattr(self, key, state[key]) def dump_network_state(self): return util.yaml_dumps(self._network_state) def as_dict(self): return {'version': self._version, 'config': self._config} def get_network_state(self): ns = self.network_state return ns def parse_config(self, skip_broken=True): if self._version == 1: self.parse_config_v1(skip_broken=skip_broken) self._parsed = True elif self._version == 2: self.parse_config_v2(skip_broken=skip_broken) self._parsed = True def parse_config_v1(self, skip_broken=True): for command in self._config: command_type = command['type'] try: handler = self.command_handlers[command_type] except KeyError: raise RuntimeError("No handler found for" " command '%s'" % command_type) try: handler(self, command) except InvalidCommand: if not skip_broken: raise else: LOG.warning("Skipping invalid command: %s", command, exc_info=True) LOG.debug(self.dump_network_state()) def parse_config_v2(self, skip_broken=True): for command_type, command in self._config.items(): if command_type == 'version': continue try: handler = self.command_handlers[command_type] except KeyError: raise RuntimeError("No handler found for" " command '%s'" % command_type) try: handler(self, command) self._v2_common(command) except InvalidCommand: if not skip_broken: raise else: LOG.warning("Skipping invalid command: %s", command, exc_info=True) LOG.debug(self.dump_network_state()) @ensure_command_keys(['name']) def handle_loopback(self, command): return self.handle_physical(command) @ensure_command_keys(['name']) def handle_physical(self, command): ''' command = { 'type': 'physical', 'mac_address': 'c0:d6:9f:2c:e8:80', 'name': 'eth0', 'subnets': [ {'type': 'dhcp4'} ] } ''' interfaces = self._network_state.get('interfaces', {}) iface = interfaces.get(command['name'], {}) for param, val in command.get('params', {}).items(): iface.update({param: val}) # convert subnet ipv6 netmask to cidr as needed subnets = _normalize_subnets(command.get('subnets')) # automatically set 'use_ipv6' if any addresses are ipv6 if not self.use_ipv6: for subnet in subnets: if (subnet.get('type').endswith('6') or is_ipv6_addr(subnet.get('address'))): self.use_ipv6 = True break iface.update({ 'name': command.get('name'), 'type': command.get('type'), 'mac_address': command.get('mac_address'), 'inet': 'inet', 'mode': 'manual', 'mtu': command.get('mtu'), 'address': None, 'gateway': None, 'subnets': subnets, }) self._network_state['interfaces'].update({command.get('name'): iface}) self.dump_network_state() @ensure_command_keys(['name', 'vlan_id', 'vlan_link']) def handle_vlan(self, command): ''' auto eth0.222 iface eth0.222 inet static address 10.10.10.1 netmask 255.255.255.0 hwaddress ether BC:76:4E:06:96:B3 vlan-raw-device eth0 ''' interfaces = self._network_state.get('interfaces', {}) self.handle_physical(command) iface = interfaces.get(command.get('name'), {}) iface['vlan-raw-device'] = command.get('vlan_link') iface['vlan_id'] = command.get('vlan_id') interfaces.update({iface['name']: iface}) @ensure_command_keys(['name', 'bond_interfaces', 'params']) def handle_bond(self, command): ''' #/etc/network/interfaces auto eth0 iface eth0 inet manual bond-master bond0 bond-mode 802.3ad auto eth1 iface eth1 inet manual bond-master bond0 bond-mode 802.3ad auto bond0 iface bond0 inet static address 192.168.0.10 gateway 192.168.0.1 netmask 255.255.255.0 bond-slaves none bond-mode 802.3ad bond-miimon 100 bond-downdelay 200 bond-updelay 200 bond-lacp-rate 4 ''' self.handle_physical(command) interfaces = self._network_state.get('interfaces') iface = interfaces.get(command.get('name'), {}) for param, val in command.get('params').items(): iface.update({param: val}) iface.update({'bond-slaves': 'none'}) self._network_state['interfaces'].update({iface['name']: iface}) # handle bond slaves for ifname in command.get('bond_interfaces'): if ifname not in interfaces: cmd = { 'name': ifname, 'type': 'bond', } # inject placeholder self.handle_physical(cmd) interfaces = self._network_state.get('interfaces', {}) bond_if = interfaces.get(ifname) bond_if['bond-master'] = command.get('name') # copy in bond config into slave for param, val in command.get('params').items(): bond_if.update({param: val}) self._network_state['interfaces'].update({ifname: bond_if}) @ensure_command_keys(['name', 'bridge_interfaces']) def handle_bridge(self, command): ''' auto br0 iface br0 inet static address 10.10.10.1 netmask 255.255.255.0 bridge_ports eth0 eth1 bridge_stp off bridge_fd 0 bridge_maxwait 0 bridge_params = [ "bridge_ports", "bridge_ageing", "bridge_bridgeprio", "bridge_fd", "bridge_gcint", "bridge_hello", "bridge_hw", "bridge_maxage", "bridge_maxwait", "bridge_pathcost", "bridge_portprio", "bridge_stp", "bridge_waitport", ] ''' # find one of the bridge port ifaces to get mac_addr # handle bridge_slaves interfaces = self._network_state.get('interfaces', {}) for ifname in command.get('bridge_interfaces'): if ifname in interfaces: continue cmd = { 'name': ifname, } # inject placeholder self.handle_physical(cmd) interfaces = self._network_state.get('interfaces', {}) self.handle_physical(command) iface = interfaces.get(command.get('name'), {}) iface['bridge_ports'] = command['bridge_interfaces'] for param, val in command.get('params', {}).items(): iface.update({param: val}) # convert value to boolean bridge_stp = iface.get('bridge_stp') if bridge_stp is not None and type(bridge_stp) != bool: if bridge_stp in ['on', '1', 1]: bridge_stp = True elif bridge_stp in ['off', '0', 0]: bridge_stp = False else: raise ValueError( 'Cannot convert bridge_stp value ({stp}) to' ' boolean'.format(stp=bridge_stp)) iface.update({'bridge_stp': bridge_stp}) interfaces.update({iface['name']: iface}) @ensure_command_keys(['name']) def handle_infiniband(self, command): self.handle_physical(command) @ensure_command_keys(['address']) def handle_nameserver(self, command): dns = self._network_state.get('dns') if 'address' in command: addrs = command['address'] if not type(addrs) == list: addrs = [addrs] for addr in addrs: dns['nameservers'].append(addr) if 'search' in command: paths = command['search'] if not isinstance(paths, list): paths = [paths] for path in paths: dns['search'].append(path) @ensure_command_keys(['destination']) def handle_route(self, command): self._network_state['routes'].append(_normalize_route(command)) # V2 handlers def handle_bonds(self, command): ''' v2_command = { bond0: { 'interfaces': ['interface0', 'interface1'], 'parameters': { 'mii-monitor-interval': 100, 'mode': '802.3ad', 'xmit_hash_policy': 'layer3+4'}}, bond1: { 'bond-slaves': ['interface2', 'interface7'], 'parameters': { 'mode': 1, } } } v1_command = { 'type': 'bond' 'name': 'bond0', 'bond_interfaces': [interface0, interface1], 'params': { 'bond-mode': '802.3ad', 'bond_miimon: 100, 'bond_xmit_hash_policy': 'layer3+4', } } ''' self._handle_bond_bridge(command, cmd_type='bond') def handle_bridges(self, command): ''' v2_command = { br0: { 'interfaces': ['interface0', 'interface1'], 'forward-delay': 0, 'stp': False, 'maxwait': 0, } } v1_command = { 'type': 'bridge' 'name': 'br0', 'bridge_interfaces': [interface0, interface1], 'params': { 'bridge_stp': 'off', 'bridge_fd: 0, 'bridge_maxwait': 0 } } ''' self._handle_bond_bridge(command, cmd_type='bridge') def handle_ethernets(self, command): ''' ethernets: eno1: match: macaddress: 00:11:22:33:44:55 wakeonlan: true dhcp4: true dhcp6: false addresses: - 192.168.14.2/24 - 2001:1::1/64 gateway4: 192.168.14.1 gateway6: 2001:1::2 nameservers: search: [foo.local, bar.local] addresses: [8.8.8.8, 8.8.4.4] lom: match: driver: ixgbe set-name: lom1 dhcp6: true switchports: match: name: enp2* mtu: 1280 command = { 'type': 'physical', 'mac_address': 'c0:d6:9f:2c:e8:80', 'name': 'eth0', 'subnets': [ {'type': 'dhcp4'} ] } ''' for eth, cfg in command.items(): phy_cmd = { 'type': 'physical', 'name': cfg.get('set-name', eth), } mac_address = cfg.get('match', {}).get('macaddress', None) if not mac_address: LOG.debug('NetworkState Version2: missing "macaddress" info ' 'in config entry: %s: %s', eth, str(cfg)) phy_cmd.update({'mac_address': mac_address}) for key in ['mtu', 'match', 'wakeonlan']: if key in cfg: phy_cmd.update({key: cfg.get(key)}) subnets = self._v2_to_v1_ipcfg(cfg) if len(subnets) > 0: phy_cmd.update({'subnets': subnets}) LOG.debug('v2(ethernets) -> v1(physical):\n%s', phy_cmd) self.handle_physical(phy_cmd) def handle_vlans(self, command): ''' v2_vlans = { 'eth0.123': { 'id': 123, 'link': 'eth0', 'dhcp4': True, } } v1_command = { 'type': 'vlan', 'name': 'eth0.123', 'vlan_link': 'eth0', 'vlan_id': 123, 'subnets': [{'type': 'dhcp4'}], } ''' for vlan, cfg in command.items(): vlan_cmd = { 'type': 'vlan', 'name': vlan, 'vlan_id': cfg.get('id'), 'vlan_link': cfg.get('link'), } subnets = self._v2_to_v1_ipcfg(cfg) if len(subnets) > 0: vlan_cmd.update({'subnets': subnets}) LOG.debug('v2(vlans) -> v1(vlan):\n%s', vlan_cmd) self.handle_vlan(vlan_cmd) def handle_wifis(self, command): LOG.warning('Wifi configuration is only available to distros with' 'netplan rendering support.') def _v2_common(self, cfg): LOG.debug('v2_common: handling config:\n%s', cfg) if 'nameservers' in cfg: search = cfg.get('nameservers').get('search', []) dns = cfg.get('nameservers').get('addresses', []) name_cmd = {'type': 'nameserver'} if len(search) > 0: name_cmd.update({'search': search}) if len(dns) > 0: name_cmd.update({'addresses': dns}) LOG.debug('v2(nameserver) -> v1(nameserver):\n%s', name_cmd) self.handle_nameserver(name_cmd) def _handle_bond_bridge(self, command, cmd_type=None): """Common handler for bond and bridge types""" # inverse mapping for v2 keynames to v1 keynames v2key_to_v1 = dict((v, k) for k, v in NET_CONFIG_TO_V2.get(cmd_type).items()) for item_name, item_cfg in command.items(): item_params = dict((key, value) for (key, value) in item_cfg.items() if key not in NETWORK_V2_KEY_FILTER) v1_cmd = { 'type': cmd_type, 'name': item_name, cmd_type + '_interfaces': item_cfg.get('interfaces'), 'params': dict((v2key_to_v1[k], v) for k, v in item_params.get('parameters', {}).items()) } subnets = self._v2_to_v1_ipcfg(item_cfg) if len(subnets) > 0: v1_cmd.update({'subnets': subnets}) LOG.debug('v2(%s) -> v1(%s):\n%s', cmd_type, cmd_type, v1_cmd) if cmd_type == "bridge": self.handle_bridge(v1_cmd) elif cmd_type == "bond": self.handle_bond(v1_cmd) else: raise ValueError('Unknown command type: {cmd_type}'.format( cmd_type=cmd_type)) def _v2_to_v1_ipcfg(self, cfg): """Common ipconfig extraction from v2 to v1 subnets array.""" subnets = [] if 'dhcp4' in cfg: subnets.append({'type': 'dhcp4'}) if 'dhcp6' in cfg: self.use_ipv6 = True subnets.append({'type': 'dhcp6'}) gateway4 = None gateway6 = None nameservers = {} for address in cfg.get('addresses', []): subnet = { 'type': 'static', 'address': address, } if ":" in address: if 'gateway6' in cfg and gateway6 is None: gateway6 = cfg.get('gateway6') subnet.update({'gateway': gateway6}) else: if 'gateway4' in cfg and gateway4 is None: gateway4 = cfg.get('gateway4') subnet.update({'gateway': gateway4}) if 'nameservers' in cfg and not nameservers: addresses = cfg.get('nameservers').get('addresses') if addresses: nameservers['dns_nameservers'] = addresses search = cfg.get('nameservers').get('search') if search: nameservers['dns_search'] = search subnet.update(nameservers) subnets.append(subnet) routes = [] for route in cfg.get('routes', []): routes.append(_normalize_route( {'destination': route.get('to'), 'gateway': route.get('via')})) # v2 routes are bound to the interface, in v1 we add them under # the first subnet since there isn't an equivalent interface level. if len(subnets) and len(routes): subnets[0]['routes'] = routes return subnets def _normalize_subnet(subnet): # Prune all keys with None values. subnet = copy.deepcopy(subnet) normal_subnet = dict((k, v) for k, v in subnet.items() if v) if subnet.get('type') in ('static', 'static6'): normal_subnet.update( _normalize_net_keys(normal_subnet, address_keys=('address',))) normal_subnet['routes'] = [_normalize_route(r) for r in subnet.get('routes', [])] def listify(snet, name): if name in snet and not isinstance(snet[name], list): snet[name] = snet[name].split() for k in ('dns_search', 'dns_nameservers'): listify(normal_subnet, k) return normal_subnet def _normalize_net_keys(network, address_keys=()): """Normalize dictionary network keys returning prefix and address keys. @param network: A dict of network-related definition containing prefix, netmask and address_keys. @param address_keys: A tuple of keys to search for representing the address or cidr. The first address_key discovered will be used for normalization. @returns: A dict containing normalized prefix and matching addr_key. """ net = dict((k, v) for k, v in network.items() if v) addr_key = None for key in address_keys: if net.get(key): addr_key = key break if not addr_key: message = ( 'No config network address keys [%s] found in %s' % (','.join(address_keys), network)) LOG.error(message) raise ValueError(message) addr = net.get(addr_key) ipv6 = is_ipv6_addr(addr) netmask = net.get('netmask') if "/" in addr: addr_part, _, maybe_prefix = addr.partition("/") net[addr_key] = addr_part try: prefix = int(maybe_prefix) except ValueError: # this supports input of
/255.255.255.0 prefix = mask_to_net_prefix(maybe_prefix) elif netmask: prefix = mask_to_net_prefix(netmask) elif 'prefix' in net: prefix = int(net['prefix']) else: prefix = 64 if ipv6 else 24 if 'prefix' in net and str(net['prefix']) != str(prefix): LOG.warning("Overwriting existing 'prefix' with '%s' in " "network info: %s", prefix, net) net['prefix'] = prefix if ipv6: # TODO: we could/maybe should add this back with the very uncommon # 'netmask' for ipv6. We need a 'net_prefix_to_ipv6_mask' for that. if 'netmask' in net: del net['netmask'] else: net['netmask'] = net_prefix_to_ipv4_mask(net['prefix']) return net def _normalize_route(route): """normalize a route. return a dictionary with only: 'type': 'route' (only present if it was present in input) 'network': the network portion of the route as a string. 'prefix': the network prefix for address as an integer. 'metric': integer metric (only if present in input). 'netmask': netmask (string) equivalent to prefix iff network is ipv4. """ # Prune None-value keys. Specifically allow 0 (a valid metric). normal_route = dict((k, v) for k, v in route.items() if v not in ("", None)) if 'destination' in normal_route: normal_route['network'] = normal_route['destination'] del normal_route['destination'] normal_route.update( _normalize_net_keys( normal_route, address_keys=('network', 'destination'))) metric = normal_route.get('metric') if metric: try: normal_route['metric'] = int(metric) except ValueError: raise TypeError( 'Route config metric {} is not an integer'.format(metric)) return normal_route def _normalize_subnets(subnets): if not subnets: subnets = [] return [_normalize_subnet(s) for s in subnets] def is_ipv6_addr(address): if not address: return False return ":" in str(address) def subnet_is_ipv6(subnet): """Common helper for checking network_state subnets for ipv6.""" # 'static6' or 'dhcp6' if subnet['type'].endswith('6'): # This is a request for DHCPv6. return True elif subnet['type'] == 'static' and is_ipv6_addr(subnet.get('address')): return True return False def net_prefix_to_ipv4_mask(prefix): """Convert a network prefix to an ipv4 netmask. This is the inverse of ipv4_mask_to_net_prefix. 24 -> "255.255.255.0" Also supports input as a string.""" mask = socket.inet_ntoa( struct.pack(">I", (0xffffffff << (32 - int(prefix)) & 0xffffffff))) return mask def ipv4_mask_to_net_prefix(mask): """Convert an ipv4 netmask into a network prefix length. If the input is already an integer or a string representation of an integer, then int(mask) will be returned. "255.255.255.0" => 24 str(24) => 24 "24" => 24 """ if isinstance(mask, int): return mask if isinstance(mask, six.string_types): try: return int(mask) except ValueError: pass else: raise TypeError("mask '%s' is not a string or int") if '.' not in mask: raise ValueError("netmask '%s' does not contain a '.'" % mask) toks = mask.split(".") if len(toks) != 4: raise ValueError("netmask '%s' had only %d parts" % (mask, len(toks))) return sum([bin(int(x)).count('1') for x in toks]) def ipv6_mask_to_net_prefix(mask): """Convert an ipv6 netmask (very uncommon) or prefix (64) to prefix. If 'mask' is an integer or string representation of one then int(mask) will be returned. """ if isinstance(mask, int): return mask if isinstance(mask, six.string_types): try: return int(mask) except ValueError: pass else: raise TypeError("mask '%s' is not a string or int") if ':' not in mask: raise ValueError("mask '%s' does not have a ':'") bitCount = [0, 0x8000, 0xc000, 0xe000, 0xf000, 0xf800, 0xfc00, 0xfe00, 0xff00, 0xff80, 0xffc0, 0xffe0, 0xfff0, 0xfff8, 0xfffc, 0xfffe, 0xffff] prefix = 0 for word in mask.split(':'): if not word or int(word, 16) == 0: break prefix += bitCount.index(int(word, 16)) return prefix def mask_to_net_prefix(mask): """Return the network prefix for the netmask provided. Supports ipv4 or ipv6 netmasks.""" try: # if 'mask' is a prefix that is an integer. # then just return it. return int(mask) except ValueError: pass if is_ipv6_addr(mask): return ipv6_mask_to_net_prefix(mask) else: return ipv4_mask_to_net_prefix(mask) def mask_and_ipv4_to_bcast_addr(mask, ip): """Calculate the broadcast address from the subnet mask and ip addr. Supports ipv4 only.""" ip_bin = int(''.join([bin(int(x) + 256)[3:] for x in ip.split('.')]), 2) mask_dec = ipv4_mask_to_net_prefix(mask) bcast_bin = ip_bin | (2**(32 - mask_dec) - 1) bcast_str = '.'.join([str(bcast_bin >> (i << 3) & 0xFF) for i in range(4)[::-1]]) return bcast_str # vi: ts=4 expandtab