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dhcp_relay.py
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dhcp_relay.py
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#!/usr/bin/env python3
#
# Copyright (C) 2018-2020 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 os
from jinja2 import FileSystemLoader, Environment
from sys import exit
from vyos.config import Config
from vyos.defaults import directories as vyos_data_dir
from vyos import ConfigError
from vyos.util import run
config_file = r'/etc/default/isc-dhcp-relay'
default_config_data = {
'interface': [],
'server': [],
'options': [],
'hop_count': '10',
'relay_agent_packets': 'forward'
}
def get_config():
relay = default_config_data
conf = Config()
if not conf.exists(['service', 'dhcp-relay']):
return None
else:
conf.set_level(['service', 'dhcp-relay'])
# Network interfaces to listen on
if conf.exists(['interface']):
relay['interface'] = conf.return_values(['interface'])
# Servers equal to the address of the DHCP server(s)
if conf.exists(['server']):
relay['server'] = conf.return_values(['server'])
conf.set_level(['service', 'dhcp-relay', 'relay-options'])
if conf.exists(['hop-count']):
count = '-c ' + conf.return_value(['hop-count'])
relay['options'].append(count)
# Specify the maximum packet size to send to a DHCPv4/BOOTP server.
# This might be done to allow sufficient space for addition of relay agent
# options while still fitting into the Ethernet MTU size.
#
# Available in DHCPv4 mode only:
if conf.exists(['max-size']):
size = '-A ' + conf.return_value(['max-size'])
relay['options'].append(size)
# Control the handling of incoming DHCPv4 packets which already contain
# relay agent options. If such a packet does not have giaddr set in its
# header, the DHCP standard requires that the packet be discarded. However,
# if giaddr is set, the relay agent may handle the situation in four ways:
# It may append its own set of relay options to the packet, leaving the
# supplied option field intact; it may replace the existing agent option
# field; it may forward the packet unchanged; or, it may discard it.
#
# Available in DHCPv4 mode only:
if conf.exists(['relay-agents-packets']):
pkt = '-a -m ' + conf.return_value(['relay-agents-packets'])
relay['options'].append(pkt)
return relay
def verify(relay):
# bail out early - looks like removal from running config
if relay is None:
return None
if 'lo' in relay['interface']:
raise ConfigError('DHCP relay does not support the loopback interface.')
if len(relay['server']) == 0:
raise ConfigError('No DHCP relay server(s) configured.\n' \
'At least one DHCP relay server required.')
return None
def generate(relay):
# bail out early - looks like removal from running config
if relay is None:
return None
# Prepare Jinja2 template loader from files
tmpl_path = os.path.join(vyos_data_dir['data'], 'templates', 'dhcp-relay')
fs_loader = FileSystemLoader(tmpl_path)
env = Environment(loader=fs_loader)
tmpl = env.get_template('config.tmpl')
config_text = tmpl.render(relay)
with open(config_file, 'w') as f:
f.write(config_text)
return None
def apply(relay):
if relay is not None:
run('sudo systemctl restart isc-dhcp-relay.service')
else:
# DHCP relay support is removed in the commit
run('sudo systemctl stop isc-dhcp-relay.service')
os.unlink(config_file)
return None
if __name__ == '__main__':
try:
c = get_config()
verify(c)
generate(c)
apply(c)
except ConfigError as e:
print(e)
exit(1)

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