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vrf.py
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vrf.py
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#!/usr/bin/env python3
#
# Copyright (C) 2020-2022 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 sys import exit
from json import loads
from vyos.config import Config
from vyos.configdict import node_changed
from vyos.ifconfig import Interface
from vyos.template import render
from vyos.util import call
from vyos.util import cmd
from vyos.util import dict_search
from vyos.util import get_interface_config
from vyos.util import popen
from vyos.util import run
from vyos.util import sysctl
from vyos import ConfigError
from vyos import frr
from vyos import airbag
airbag.enable()
config_file = '/etc/iproute2/rt_tables.d/vyos-vrf.conf'
nft_vrf_config = '/tmp/nftables-vrf-zones'
def has_rule(af : str, priority : int, table : str):
""" Check if a given ip rule exists """
if af not in ['-4', '-6']:
raise ValueError()
command = f'ip -j {af} rule show'
for tmp in loads(cmd(command)):
if {'priority', 'table'} <= set(tmp):
if tmp['priority'] == priority and tmp['table'] == table:
return True
return False
def vrf_interfaces(c, match):
matched = []
old_level = c.get_level()
c.set_level(['interfaces'])
section = c.get_config_dict([], get_first_key=True)
for type in section:
interfaces = section[type]
for name in interfaces:
interface = interfaces[name]
if 'vrf' in interface:
v = interface.get('vrf', '')
if v == match:
matched.append(name)
c.set_level(old_level)
return matched
def vrf_routing(c, match):
matched = []
old_level = c.get_level()
c.set_level(['protocols', 'vrf'])
if match in c.list_nodes([]):
matched.append(match)
c.set_level(old_level)
return matched
def get_config(config=None):
if config:
conf = config
else:
conf = Config()
base = ['vrf']
vrf = conf.get_config_dict(base, get_first_key=True)
# determine which VRF has been removed
for name in node_changed(conf, base + ['name']):
if 'vrf_remove' not in vrf:
vrf.update({'vrf_remove' : {}})
vrf['vrf_remove'][name] = {}
# get VRF bound interfaces
interfaces = vrf_interfaces(conf, name)
if interfaces: vrf['vrf_remove'][name]['interface'] = interfaces
# get VRF bound routing instances
routes = vrf_routing(conf, name)
if routes: vrf['vrf_remove'][name]['route'] = routes
return vrf
def verify(vrf):
# ensure VRF is not assigned to any interface
if 'vrf_remove' in vrf:
for name, config in vrf['vrf_remove'].items():
if 'interface' in config:
raise ConfigError(f'Can not remove VRF "{name}", it still has '\
f'member interfaces!')
if 'route' in config:
raise ConfigError(f'Can not remove VRF "{name}", it still has '\
f'static routes installed!')
if 'name' in vrf:
table_ids = []
for name, config in vrf['name'].items():
# table id is mandatory
if 'table' not in config:
raise ConfigError(f'VRF "{name}" table id is mandatory!')
# routing table id can't be changed - OS restriction
if os.path.isdir(f'/sys/class/net/{name}'):
tmp = str(dict_search('linkinfo.info_data.table', get_interface_config(name)))
if tmp and tmp != config['table']:
raise ConfigError(f'VRF "{name}" table id modification not possible!')
# VRf routing table ID must be unique on the system
if config['table'] in table_ids:
raise ConfigError(f'VRF "{name}" table id is not unique!')
table_ids.append(config['table'])
return None
def generate(vrf):
render(config_file, 'vrf/vrf.conf.tmpl', vrf)
# Render nftables zones config
render(nft_vrf_config, 'firewall/nftables-vrf-zones.tmpl', vrf)
return None
def apply(vrf):
# Documentation
#
# - https://github.com/torvalds/linux/blob/master/Documentation/networking/vrf.txt
# - https://github.com/Mellanox/mlxsw/wiki/Virtual-Routing-and-Forwarding-(VRF)
# - https://github.com/Mellanox/mlxsw/wiki/L3-Tunneling
# - https://netdevconf.info/1.1/proceedings/slides/ahern-vrf-tutorial.pdf
# - https://netdevconf.info/1.2/slides/oct6/02_ahern_what_is_l3mdev_slides.pdf
# set the default VRF global behaviour
bind_all = '0'
if 'bind-to-all' in vrf:
bind_all = '1'
sysctl('net.ipv4.tcp_l3mdev_accept', bind_all)
sysctl('net.ipv4.udp_l3mdev_accept', bind_all)
for tmp in (dict_search('vrf_remove', vrf) or []):
if os.path.isdir(f'/sys/class/net/{tmp}'):
call(f'ip link delete dev {tmp}')
# Remove nftables conntrack zone map item
nft_del_element = f'delete element inet vrf_zones ct_iface_map {{ "{tmp}" }}'
cmd(f'nft {nft_del_element}')
if 'name' in vrf:
# Separate VRFs in conntrack table
# check if table already exists
_, err = popen('nft list table inet vrf_zones')
# If not, create a table
if err and os.path.exists(nft_vrf_config):
cmd(f'nft -f {nft_vrf_config}')
os.unlink(nft_vrf_config)
# Linux routing uses rules to find tables - routing targets are then
# looked up in those tables. If the lookup got a matching route, the
# process ends.
#
# TL;DR; first table with a matching entry wins!
#
# You can see your routing table lookup rules using "ip rule", sadly the
# local lookup is hit before any VRF lookup. Pinging an addresses from the
# VRF will usually find a hit in the local table, and never reach the VRF
# routing table - this is usually not what you want. Thus we will
# re-arrange the tables and move the local lookup further down once VRFs
# are enabled.
#
# Thanks to https://stbuehler.de/blog/article/2020/02/29/using_vrf__virtual_routing_and_forwarding__on_linux.html
for afi in ['-4', '-6']:
# move lookup local to pref 32765 (from 0)
if not has_rule(afi, 32765, 'local'):
call(f'ip {afi} rule add pref 32765 table local')
if has_rule(afi, 0, 'local'):
call(f'ip {afi} rule del pref 0')
# make sure that in VRFs after failed lookup in the VRF specific table
# nothing else is reached
if not has_rule(afi, 1000, 'l3mdev'):
# this should be added by the kernel when a VRF is created
# add it here for completeness
call(f'ip {afi} rule add pref 1000 l3mdev protocol kernel')
# add another rule with an unreachable target which only triggers in VRF context
# if a route could not be reached
if not has_rule(afi, 2000, 'l3mdev'):
call(f'ip {afi} rule add pref 2000 l3mdev unreachable')
for name, config in vrf['name'].items():
table = config['table']
if not os.path.isdir(f'/sys/class/net/{name}'):
# For each VRF apart from your default context create a VRF
# interface with a separate routing table
call(f'ip link add {name} type vrf table {table}')
# set VRF description for e.g. SNMP monitoring
vrf_if = Interface(name)
# We also should add proper loopback IP addresses to the newly
# created VRFs for services bound to the loopback address (SNMP, NTP)
vrf_if.add_addr('127.0.0.1/8')
vrf_if.add_addr('::1/128')
# add VRF description if available
vrf_if.set_alias(config.get('description', ''))
# Enable/Disable of an interface must always be done at the end of the
# derived class to make use of the ref-counting set_admin_state()
# function. We will only enable the interface if 'up' was called as
# often as 'down'. This is required by some interface implementations
# as certain parameters can only be changed when the interface is
# in admin-down state. This ensures the link does not flap during
# reconfiguration.
state = 'down' if 'disable' in config else 'up'
vrf_if.set_admin_state(state)
# Add nftables conntrack zone map item
nft_add_element = f'add element inet vrf_zones ct_iface_map {{ "{name}" : {table} }}'
cmd(f'nft {nft_add_element}')
# return to default lookup preference when no VRF is configured
if 'name' not in vrf:
# Remove VRF zones table from nftables
tmp = run('nft list table inet vrf_zones')
if tmp == 0:
cmd('nft delete table inet vrf_zones')
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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