dhcp_server.py
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dhcp_server.py
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	#!/usr/bin/env python3
	#
	# Copyright (C) 2018 VyOS maintainers and contributors
	#
	# This program is free software; you can redistribute it and/or modify
	# it under the terms of the GNU General Public License version 2 or later as
	# published by the Free Software Foundation.
	#
	# This program is distributed in the hope that it will be useful,
	# but WITHOUT ANY WARRANTY; without even the implied warranty of
	# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
	# GNU General Public License for more details.
	#
	# You should have received a copy of the GNU General Public License
	# along with this program. If not, see <http://www.gnu.org/licenses/>.
	#
	#

	import sys
	import os
	import ipaddress
	import jinja2
	import socket
	import struct
	import netifaces

	from vyos.config import Config
	from vyos import ConfigError

	config_file = r'/etc/dhcp/dhcpd.conf'
	lease_file = r'/config/dhcpd.leases'
	daemon_config_file = r'/etc/default/isc-dhcp-server'

	# Please be careful if you edit the template.
	config_tmpl = """
	### Autogenerated by dhcp_server.py ###

	# For options please consult the following website:
	# https://www.isc.org/wp-content/uploads/2017/08/dhcp43options.html

	log-facility local7;

	{% if hostfile_update %}
	on commit {
	set ClientName = pick-first-value(host-decl-name, option fqdn.hostname, option host-name);
	set ClientIp = binary-to-ascii(10, 8, ".", leased-address);
	set ClientMac = binary-to-ascii(16, 8, ":", substring(hardware, 1, 6));
	set ClientDomain = pick-first-value(config-option domain-name, "..YYZ!");
	execute("/usr/libexec/vyos/system/on-dhcp-event.sh", "commit", ClientName, ClientIp, ClientMac, ClientDomain);
	}

	on release {
	set ClientName = pick-first-value(host-decl-name, option fqdn.hostname, option host-name);
	set ClientIp = binary-to-ascii(10, 8, ".",leased-address);
	set ClientMac = binary-to-ascii(16, 8, ":",substring(hardware, 1, 6));
	set ClientDomain = pick-first-value(config-option domain-name, "..YYZ!");
	execute("/usr/libexec/vyos/system/on-dhcp-event.sh", "release", ClientName, ClientIp, ClientMac, ClientDomain);
	}

	on expiry {
	set ClientName = pick-first-value(host-decl-name, option fqdn.hostname, option host-name);
	set ClientIp = binary-to-ascii(10, 8, ".",leased-address);
	set ClientMac = binary-to-ascii(16, 8, ":",substring(hardware, 1, 6));
	set ClientDomain = pick-first-value(config-option domain-name, "..YYZ!");
	execute("/usr/libexec/vyos/system/on-dhcp-event.sh", "release", ClientName, ClientIp, ClientMac, ClientDomain);
	}
	{% endif %}
	ddns-update-style {% if ddns_enable -%} interim {%- else -%} none {%- endif %};
	{% if static_route -%}
	option rfc3442-static-route code 121 = array of integer 8;
	option windows-static-route code 249 = array of integer 8;
	{%- endif %}
	{% if static_route -%}
	option wpad-url code 252 = text;
	{% endif %}

	{%- if global_parameters %}
	# The following {{ global_parameters \| length }} line(s) were added as global-parameters in the CLI and have not been validated
	{%- for param in global_parameters %}
	{{ param }}
	{%- endfor -%}
	{%- endif %}

	# Failover configuration
	{% for network in shared_network %}
	{%- if not network.disabled -%}
	{%- for subnet in network.subnet %}
	{%- if subnet.failover_name -%}
	failover peer "{{ subnet.failover_name }}" {
	{%- if subnet.failover_status == 'primary' %}
	primary;
	mclt 1800;
	split 128;
	{%- elif subnet.failover_status == 'secondary' %}
	secondary;
	{%- endif %}
	address {{ subnet.failover_local_addr }};
	port 520;
	peer address {{ subnet.failover_peer_addr }};
	peer port 520;
	max-response-delay 30;
	max-unacked-updates 10;
	load balance max seconds 3;
	}
	{% endif -%}
	{% endfor -%}
	{% endif -%}
	{% endfor %}

	# Shared network configration(s)
	{% for network in shared_network %}
	{%- if not network.disabled -%}
	shared-network {{ network.name }} {
	{% if network.authoritative %}authoritative;{% endif %}
	{%- if network.network_parameters %}
	# The following {{ network.network_parameters \| length }} line(s) were added as shared-network-parameters in the CLI and have not been validated
	{%- for param in network.network_parameters %}
	{{ param }}
	{%- endfor -%}
	{%- endif %}
	{%- for subnet in network.subnet %}
	subnet {{ subnet.address }} netmask {{ subnet.netmask }} {
	{%- if subnet.dns_server %}
	option domain-name-servers {{ subnet.dns_server \| join(', ') }};
	{%- endif %}
	{%- if subnet.domain_search %}
	option domain-search {{ subnet.domain_search \| join(', ') }};
	{%- endif %}
	{%- if subnet.ntp_server %}
	option ntp-servers {{ subnet.ntp_server \| join(', ') }};
	{%- endif %}
	{%- if subnet.pop_server %}
	option pop-server {{ subnet.pop_server \| join(', ') }};
	{%- endif %}
	{%- if subnet.smtp_server %}
	option smtp-server {{ subnet.smtp_server \| join(', ') }};
	{%- endif %}
	{%- if subnet.time_server %}
	option time-servers {{ subnet.time_server \| join(', ') }};
	{%- endif %}
	{%- if subnet.wins_server %}
	option netbios-name-servers {{ subnet.wins_server \| join(', ') }};
	{%- endif %}
	{%- if subnet.static_route %}
	option rfc3442-static-route {{ subnet.static_route }};
	option windows-static-route {{ subnet.static_route }};
	{%- endif %}
	{%- if subnet.ip_forwarding %}
	option ip-forwarding true;
	{%- endif -%}
	{%- if subnet.default_router %}
	option routers {{ subnet.default_router }};
	{%- endif -%}
	{%- if subnet.server_identifier %}
	option dhcp-server-identifier {{ subnet.server_identifier }};
	{%- endif -%}
	{%- if subnet.domain_name %}
	option domain-name "{{ subnet.domain_name }}";
	{%- endif -%}
	{%- if subnet.tftp_server %}
	option tftp-server-name "{{ subnet.tftp_server }}";
	{%- endif -%}
	{%- if subnet.bootfile_name %}
	option bootfile-name "{{ subnet.bootfile_name }}";
	filename "{{ subnet.bootfile_name }}";
	{%- endif -%}
	{%- if subnet.bootfile_server %}
	next-server {{ subnet.bootfile_server }};
	{%- endif -%}
	{%- if subnet.time_offset %}
	option time-offset {{ subnet.time_offset }};
	{%- endif -%}
	{%- if subnet.wpad_url %}
	option wpad-url "{{ subnet.wpad_url }}";
	{%- endif -%}
	{%- if subnet.client_prefix_length %}
	option subnet-mask {{ subnet.client_prefix_length }};
	{%- endif -%}
	{% if subnet.lease %}
	default-lease-time {{ subnet.lease }};
	max-lease-time {{ subnet.lease }};
	{%- endif -%}
	{%- for host in subnet.static_mapping %}
	{% if not host.disabled -%}
	host {{ network.name }}_{{ host.name }} {
	fixed-address {{ host.ip_address }};
	hardware ethernet {{ host.mac_address }};
	{%- if host.static_parameters %}
	# The following {{ host.static_parameters \| length }} line(s) were added as static-mapping-parameters in the CLI and have not been validated
	{%- for param in host.static_parameters %}
	{{ param }}
	{%- endfor -%}
	{%- endif %}
	}
	{%- endif %}
	{%- endfor %}
	{%- for range in subnet.range %}
	range {{ range.start }} {{ range.stop }};
	{%- endfor %}
	}
	{%- endfor %}
	on commit { set shared-networkname = "{{ network.name }}"; }
	}
	{%- endif %}
	{% endfor %}
	"""

	daemon_tmpl = """
	### Autogenerated by dhcp_server.py ###

	# sourced by /etc/init.d/isc-dhcp-server

	DHCPD_CONF=/etc/dhcp/dhcpd.conf
	DHCPD_PID=/var/run/dhcpd.pid
	OPTIONS="-4 -lf {{ lease_file }}"
	INTERFACES=""
	"""

	default_config_data = {
	'lease_file': lease_file,
	'disabled': False,
	'ddns_enable': False,
	'global_parameters': [],
	'hostfile_update': False,
	'static_route': False,
	'wpad': False,
	'shared_network': [],
	}

	def get_config():
	dhcp = default_config_data
	conf = Config()
	if not conf.exists('service dhcp-server'):
	return None
	else:
	conf.set_level('service dhcp-server')

	# check for global disable of DHCP service
	if conf.exists('disable'):
	dhcp['disabled'] = True

	# check for global dynamic DNS upste
	if conf.exists('dynamic-dns-update'):
	dhcp['ddns_enable'] = True

	# HACKS AND TRICKS
	#
	# check for global 'raw' ISC DHCP parameters configured by users
	# actually this is a bad idea in general to pass raw parameters from any user
	if conf.exists('global-parameters'):
	dhcp['global_parameters'] = conf.return_values('global-parameters')

	# check for global DHCP server updating /etc/host per lease
	if conf.exists('hostfile-update'):
	dhcp['hostfile_update'] = True

	# check for multiple, shared networks served with DHCP addresses
	if conf.exists('shared-network-name'):
	for network in conf.list_nodes('shared-network-name'):
	conf.set_level('service dhcp-server shared-network-name {0}'.format(network))
	config = {
	'name': network,
	'authoritative': False,
	'description': '',
	'disabled': False,
	'network_parameters': [],
	'subnet': []
	}
	# check if DHCP server should be authoritative on this network
	if conf.exists('authoritative'):
	config['authoritative'] = True

	# A description for this given network
	if conf.exists('description'):
	config['description'] = conf.return_value('description')

	# If disabled, the shared-network configuration becomes inactive in
	# the running DHCP server instance
	if conf.exists('disable'):
	config['disabled'] = True

	# HACKS AND TRICKS
	#
	# check for 'raw' ISC DHCP parameters configured by users
	# actually this is a bad idea in general to pass raw parameters
	# from any user
	#
	# deprecate this and issue a warning like we do for DNS forwarding?
	if conf.exists('shared-network-parameters'):
	config['network_parameters'] = conf.return_values('shared-network-parameters')

	# check for multiple subnet configurations in a shared network
	# config segment
	if conf.exists('subnet'):
	for net in conf.list_nodes('subnet'):
	conf.set_level('service dhcp-server shared-network-name {0} subnet {1}'.format(network, net))
	subnet = {
	'network': net,
	'address': str(ipaddress.ip_network(net).network_address),
	'netmask': str(ipaddress.ip_network(net).netmask),
	'bootfile_name': '',
	'bootfile_server': '',
	'client_prefix_length': '',
	'default_router': '',
	'dns_server': [],
	'domain_name': '',
	'domain_search': [],
	'exclude': [],
	'failover_local_addr': '',
	'failover_name': '',
	'failover_peer_addr': '',
	'failover_status': '',
	'ip_forwarding': False,
	'lease': '86400',
	'ntp_server': [],
	'pop_server': [],
	'server_identifier': '',
	'smtp_server': [],
	'range': [],
	'static_mapping': [],
	'static_subnet': '',
	'static_router': '',
	'static_route': '',
	'subnet_parameters': [],
	'tftp_server': '',
	'time_offset': '',
	'time_server': [],
	'wins_server': [],
	'wpad_url': ''
	}

	# Used to identify a bootstrap file
	if conf.exists('bootfile-name'):
	subnet['bootfile_name'] = conf.return_value('bootfile-name')

	# Specify host address of the server from which the initial boot file
	# (specified above) is to be loaded. Should be a numeric IP address or
	# domain name.
	if conf.exists('bootfile-server'):
	subnet['bootfile_server'] = conf.return_value('bootfile-server')

	# The subnet mask option specifies the client's subnet mask as per RFC 950. If no subnet
	# mask option is provided anywhere in scope, as a last resort dhcpd will use the subnet
	# mask from the subnet declaration for the network on which an address is being assigned.
	if conf.exists('client-prefix-length'):
	# snippet borrowed from https://stackoverflow.com/questions/33750233/convert-cidr-to-subnet-mask-in-python
	host_bits = 32 - int(conf.return_value('client-prefix-length'))
	subnet['client_prefix_length'] = socket.inet_ntoa(struct.pack('!I', (1 << 32) - (1 << host_bits)))

	# Default router IP address on the client's subnet
	if conf.exists('default-router'):
	subnet['default_router'] = conf.return_value('default-router')

	# Specifies a list of Domain Name System (STD 13, RFC 1035) name servers available to
	# the client. Servers should be listed in order of preference.
	if conf.exists('dns-server'):
	subnet['dns_server'] = conf.return_values('dns-server')

	# Option specifies the domain name that client should use when resolving hostnames
	# via the Domain Name System.
	if conf.exists('domain-name'):
	subnet['domain_name'] = conf.return_value('domain-name')

	# The domain-search option specifies a 'search list' of Domain Names to be used
	# by the client to locate not-fully-qualified domain names.
	if conf.exists('domain-search'):
	for domain in conf.return_values('domain-search'):
	subnet['domain_search'].append('"' + domain + '"')

	# IP address (local) for failover peer to connect
	if conf.exists('failover local-address'):
	subnet['failover_local_addr'] = conf.return_value('failover local-address')

	# DHCP failover peer name
	if conf.exists('failover name'):
	subnet['failover_name'] = conf.return_value('failover name')

	# IP address (remote) of failover peer
	if conf.exists('failover peer-address'):
	subnet['failover_peer_addr'] = conf.return_value('failover peer-address')

	# DHCP failover peer status (primary\|secondary)
	if conf.exists('failover status'):
	subnet['failover_status'] = conf.return_value('failover status')

	# Option specifies whether the client should configure its IP layer for packet
	# forwarding
	if conf.exists('ip-forwarding'):
	subnet['ip_forwarding'] = True

	# Time should be the length in seconds that will be assigned to a lease if the
	# client requesting the lease does not ask for a specific expiration time
	if conf.exists('lease'):
	subnet['lease'] = conf.return_value('lease')

	# Specifies a list of IP addresses indicating NTP (RFC 5905) servers available
	# to the client.
	if conf.exists('ntp-server'):
	subnet['ntp_server'] = conf.return_values('ntp-server')

	# POP3 server option specifies a list of POP3 servers available to the client.
	# Servers should be listed in order of preference.
	if conf.exists('pop-server'):
	subnet['pop_server'] = conf.return_values('pop-server')

	# DHCP servers include this option in the DHCPOFFER in order to allow the client
	# to distinguish between lease offers. DHCP clients use the contents of the
	# 'server identifier' field as the destination address for any DHCP messages
	# unicast to the DHCP server
	if conf.exists('server-identifier'):
	subnet['server_identifier'] = conf.return_value('server-identifier')

	# SMTP server option specifies a list of SMTP servers available to the client.
	# Servers should be listed in order of preference.
	if conf.exists('smtp-server'):
	subnet['smtp_server'] = conf.return_values('smtp-server')

	# For any subnet on which addresses will be assigned dynamically, there must be at
	# least one range statement. The range statement gives the lowest and highest IP
	# addresses in a range. All IP addresses in the range should be in the subnet in
	# which the range statement is declared.
	if conf.exists('range'):
	for range in conf.list_nodes('range'):
	range = {
	'start': conf.return_value('range {0} start'.format(range)),
	'stop': conf.return_value('range {0} stop'.format(range))
	}
	subnet['range'].append(range)

	# IP address that needs to be excluded from DHCP lease range
	if conf.exists('exclude'):
	# We have no need to store the exclude addresses. Exclude addresses
	# are recalculated into several ranges
	exclude = []
	subnet['exclude'] = conf.return_values('exclude')
	for addr in subnet['exclude']:
	exclude.append(ipaddress.ip_address(addr))

	# sort excluded IP addresses ascending
	exclude = sorted(exclude)

	# calculate multipe ranges based on the excluded IP addresses
	output = []
	for range in subnet['range']:
	range_start = range['start']
	range_stop = range['stop']

	for i in exclude:
	# Excluded IP address must be in out specified range
	if (i >= ipaddress.ip_address(range_start)) and (i <= ipaddress.ip_address(range_stop)):
	# Build up new IP address range ending one IP address before
	# our exclude address
	range = {
	'start': str(range_start),
	'stop': str(i - 1)
	}
	# Our next IP address range will start one address after
	# our exclude address
	range_start = i + 1
	output.append(range)

	# Take care of last IP address range spanning from the last exclude
	# address (+1) to the end of the initial configured range
	if i is exclude[-1]:
	last = {
	'start': str(i + 1),
	'stop': str(range_stop)
	}
	output.append(last)
	else:
	# IP address not inside search range, take range is it is
	output.append(range)

	# We successfully build up a new list containing several IP address
	# ranges, replace IP address range in our dictionary
	subnet['range'] = output

	# Static DHCP leases
	if conf.exists('static-mapping'):
	for mapping in conf.list_nodes('static-mapping'):
	conf.set_level('service dhcp-server shared-network-name {0} subnet {1} static-mapping {2}'.format(network, net, mapping))
	mapping = {
	'name': mapping,
	'disabled': False,
	'ip_address': '',
	'mac_address': '',
	'static_parameters': []
	}

	# This static lease is disabled
	if conf.exists('disable'):
	mapping['disabled'] = True

	# IP address used for this DHCP client
	if conf.exists('ip-address'):
	mapping['ip_address'] = conf.return_value('ip-address')

	# MAC address of requesting DHCP client
	if conf.exists('mac-address'):
	mapping['mac_address'] = conf.return_value('mac-address')

	# HACKS AND TRICKS
	#
	# check for 'raw' ISC DHCP parameters configured by users
	# actually this is a bad idea in general to pass raw parameters
	# from any user
	#
	# deprecate this and issue a warning like we do for DNS forwarding?
	if conf.exists('static-mapping-parameters'):
	mapping['static_parameters'] = conf.return_values('static-mapping-parameters')

	# append static-mapping configuration to subnet list
	subnet['static_mapping'].append(mapping)

	# Reset config level to matching hirachy
	conf.set_level('service dhcp-server shared-network-name {0} subnet {1}'.format(network, net))

	# This option specifies a list of static routes that the client should install in its routing
	# cache. If multiple routes to the same destination are specified, they are listed in descending
	# order of priority.
	if conf.exists('static-route destination-subnet'):
	subnet['static_subnet'] = conf.return_value('static-route destination-subnet')
	# Required for global config section
	dhcp['static_route'] = True

	if conf.exists('static-route router'):
	subnet['static_router'] = conf.return_value('static-route router')

	if subnet['static_router'] and subnet['static_subnet']:
	# https://ercpe.de/blog/pushing-static-routes-with-isc-dhcp-server
	# Option format is:
	# <netmask>, <network-byte1>, <network-byte2>, <network-byte3>, <router-byte1>, <router-byte2>, <router-byte3>
	# where bytes with the value 0 are omitted.
	net = ipaddress.ip_network(subnet['static_subnet'])
	# add netmask
	string = str(net.prefixlen) + ','
	# add network bytes
	bytes = str(net.network_address).split('.')
	for b in bytes:
	if b != '0':
	string += b + ','

	# add router bytes
	bytes = subnet['static_router'].split('.')
	for b in bytes:
	if b != '0':
	string += b
	if b is not bytes[-1]:
	string += ','

	subnet['static_route'] = string

	# HACKS AND TRICKS
	#
	# check for 'raw' ISC DHCP parameters configured by users
	# actually this is a bad idea in general to pass raw parameters
	# from any user
	#
	# deprecate this and issue a warning like we do for DNS forwarding?
	if conf.exists('subnet-parameters'):
	config['subnet_parameters'] = conf.return_values('subnet-parameters')

	# This option is used to identify a TFTP server and, if supported by the client, should have
	# the same effect as the server-name declaration. BOOTP clients are unlikely to support this
	# option. Some DHCP clients will support it, and others actually require it.
	if conf.exists('tftp-server-name'):
	subnet['tftp_server'] = conf.return_value('tftp-server-name')

	# The time-offset option specifies the offset of the client’s subnet in seconds from
	# Coordinated Universal Time (UTC).
	if conf.exists('time-offset'):
	subnet['time_offset'] = conf.return_value('time-offset')

	# The time-server option specifies a list of RFC 868 time servers available to the client.
	# Servers should be listed in order of preference.
	if conf.exists('time-server'):
	subnet['time_server'] = conf.return_values('time-server')

	# The NetBIOS name server (NBNS) option specifies a list of RFC 1001/1002 NBNS name servers
	# listed in order of preference. NetBIOS Name Service is currently more commonly referred to
	# as WINS. WINS servers can be specified using the netbios-name-servers option.
	if conf.exists('wins-server'):
	subnet['wins_server'] = conf.return_values('wins-server')

	# URL for Web Proxy Autodiscovery Protocol
	if conf.exists('wpad-url'):
	subnet['wpad_url'] = conf.return_value('wpad-url')
	# Required for global config section
	dhcp['wpad'] = True

	# append subnet configuration to shared network subnet list
	config['subnet'].append(subnet)

	# append shared network configuration to config dictionary
	dhcp['shared_network'].append(config)

	return dhcp

	def verify(dhcp):
	if (dhcp is None) or (dhcp['disabled'] is True):
	return None

	# If DHCP is enabled we need one share-network
	if len(dhcp['shared_network']) == 0:
	raise ConfigError('No DHCP shared networks configured.\n'
	'At least one DHCP shared network must be configured.')

	# A shared-network requires a subnet definition
	for network in dhcp['shared_network']:
	if len(network['subnet']) == 0:
	raise ConfigError('No DHCP lease subnets configured for "{0}". At least one\n'
	'lease subnet must be configured for each shared network.'.format(network['name']))

	# Inspect our subnet configuration
	failover_names = []
	listen_ok = False
	subnets = []
	for network in dhcp['shared_network']:
	for subnet in network['subnet']:
	# Subnet static route declaration requires destination and router
	if subnet['static_subnet'] or subnet['static_router']:
	if not (subnet['static_subnet'] and subnet['static_router']):
	raise ConfigError('Please specify the missing DHCP static-route parameter: destination-subnet \| router')

	# Failover requires all 4 parameters set
	if subnet['failover_local_addr'] or subnet['failover_peer_addr'] or subnet['failover_name'] or subnet['failover_status']:
	if not (subnet['failover_local_addr'] and subnet['failover_peer_addr'] and subnet['failover_name'] and subnet['failover_status']):
	raise ConfigError('Please set one or more of the missing DHCP failover parameters: local-address \| peer-address \| name \| status')

	# Failover names must be uniquie
	if subnet['failover_name'] in failover_names:
	raise ConfigError('Failover names should be unique: "{0}" has already been configured.'.format(subnet['failover_name']))
	else:
	failover_names.append(subnet['failover_name'])

	# Failover requires start/stop ranges for pool
	if (len(subnet['range']) == 0):
	raise ConfigError('Atleast one start-stop range must be configured for "{0}" to set up DHCP failover.'.format(subnet['network']))

	# Check if DHCP address range is inside configured subnet declaration
	range_start = []
	range_stop = []
	for range in subnet['range']:
	# DHCP stop IP required after start IP
	if range['start'] and not range['stop']:
	raise ConfigError('DHCP range stop IP not defined for range start IP "{0}".'.format(range['start']))

	# Start address must be inside network
	if not ipaddress.ip_address(range['start']) in ipaddress.ip_network(subnet['network']):
	raise ConfigError('DHCP range start IP "{0}" is not in subnet "{1}" specified in network "{2}."'.format(range['start'], subnet['network'], network['name']))

	# Stop address must be inside network
	if not ipaddress.ip_address(range['stop']) in ipaddress.ip_network(subnet['network']):
	raise ConfigError('DHCP range stop IP "{0}" is not in subnet "{1}" specified in network "{2}."'.format(range['stop'], subnet['network'], network['name']))

	# Stop address must be greater or equal to start address
	if not ipaddress.ip_address(range['stop']) >= ipaddress.ip_address(range['start']):
	raise ConfigError('DHCP range stop IP "{0}" should be an address greater or equal to the start address "{1}".'.format(range['stop'], range['start']))

	# Range start address must be unique
	if range['start'] in range_start:
	raise ConfigError('Conflicting DHCP lease ranges: Pool start address "{0}" defined multipe times'.format(range['start']))
	else:
	range_start.append(range['start'])

	# Range stop address must be unique
	if range['stop'] in range_stop:
	raise ConfigError('Conflicting DHCP lease ranges: Pool stop address "{0}" defined multipe times'.format(range['stop']))
	else:
	range_stop.append(range['stop'])

	# Exclude addresses must be in bound
	for exclude in subnet['exclude']:
	if not ipaddress.ip_address(exclude) in ipaddress.ip_network(subnet['network']):
	raise ConfigError('Exclude IP "{0}" is outside of the DHCP lease network "{1}" under shared network "{2}".'.format(exclude, subnet['network'], network['name']))

	# At least one DHCP address range or static-mapping required
	active_mapping = False
	if (len(subnet['range']) == 0):
	for mapping in subnet['static_mapping']:
	# we need at least one active mapping
	if (not active_mapping) and (not mapping['disabled']):
	active_mapping = True
	else:
	active_mapping = True

	if not active_mapping:
	raise ConfigError('No DHCP address range or active static-mapping set for subnet "{0}".'.format(subnet['network']))

	# Static IP address mappings require both an IP address and MAC address
	for mapping in subnet['static_mapping']:
	# Static IP address must be configured
	if not mapping['ip_address']:
	raise ConfigError('No static lease IP address specified for static mapping "{0}" under shared network name "{1}".'.format(mapping['name'], network['name']))

	# Static IP address must be in bound
	if not ipaddress.ip_address(mapping['ip_address']) in ipaddress.ip_network(subnet['network']):
	raise ConfigError('Static DHCP lease IP "{0}" under static mapping "{1}" in shared network "{2}" is outside DHCP lease network "{3}".'.format(mapping['ip_address'], mapping['name'], network['name'], subnet['network'], ))

	# Static mapping requires MAC address
	if not mapping['mac_address']:
	raise ConfigError('No static lease MAC address specified for static mapping "{0}" under shared network name "{1}".'.format(mapping['name'], network['name']))

	#
	# There must be one subnet connected to a real interface
	#
	for interface in netifaces.interfaces():
	# Test if IPv4 addresses are configured at all
	if netifaces.AF_INET in netifaces.ifaddresses(interface).keys():
	# An interface can have multiple addresses, but ISC DHCP only supports the first :(
	ip = netifaces.ifaddresses(interface)[netifaces.AF_INET][0]['addr']
	if ipaddress.ip_address(ip) in ipaddress.ip_network(subnet['network']):
	# Bingo! At least one subnet connected to an interface on this machine
	listen_ok = True

	#
	# Subnets must be non overlapping
	#
	if subnet['network'] in subnets:
	raise ConfigError('Subnets must be unique! "{0}" defined multiple times.'.format(subnet))
	else:
	subnets.append(subnet['network'])

	#
	# Check for overlapping subnets
	#
	net = ipaddress.ip_network(subnet['network'])
	for n in subnets:
	net2 = ipaddress.ip_network(n)
	if (net.compare_networks(net2) != 0):
	if net.overlaps(net2):
	raise ConfigError('Conflicting subnet ranges: "{0}" overlaps "{1}"'.format(net, net2))

	if not listen_ok:
	raise ConfigError('None of the DHCP lease subnets are inside any configured subnet on\n' \
	'broadcast interfaces. At least one lease subnet must be set such that\n' \
	'DHCP server listens on a one broadcast interface')

	return None

	def generate(dhcp):
	if dhcp is None:
	return None

	if dhcp['disabled'] is True:
	print('Warning: DHCP server will be deactivated because it is disabled')
	return None

	tmpl = jinja2.Template(config_tmpl)
	config_text = tmpl.render(dhcp)
	with open(config_file, 'w') as f:
	f.write(config_text)

	tmpl = jinja2.Template(daemon_tmpl)
	config_text = tmpl.render(dhcp)
	with open(daemon_config_file, 'w') as f:
	f.write(config_text)

	return None

	def apply(dhcp):
	if (dhcp is None) or dhcp['disabled']:
	# DHCP server is removed in the commit
	os.system('sudo systemctl stop isc-dhcp-server.service')
	if os.path.exists(config_file):
	os.unlink(config_file)
	if os.path.exists(daemon_config_file):
	os.unlink(daemon_config_file)
	else:
	# If our file holding DHCP leases does yet not exist - create it
	if not os.path.exists(lease_file):
	os.mknod(lease_file)

	os.system('sudo systemctl restart isc-dhcp-server.service')

	return None

	if __name__ == '__main__':
	try:
	c = get_config()
	verify(c)
	generate(c)
	apply(c)
	except ConfigError as e:
	print(e)
	sys.exit(1)

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