Bridge или как обьединять сетевые интерфейсы

Бридж (англ. bridge, мост) - это способ соединения двух сегментов Ethernet на канальном уровне, т.е. без использования протоколов более высокого уровня, таких как IP. Пакеты передаются на основе Ethernet-адресов, а не IP-адресов (как в маршрутизаторе). Поскольку передача выполняется на канальном уровне (уровень 2 модели OSI), все протоколы более высокого уровня прозрачно проходят через мост.

Термины коммутатор, мост и бридж могут использоваться на данной странице как взаимознаменяемые.

Код bridge в Linux является частичной реализацией стандарта ANSI/IEEE 802.1d. Впервые бриджинг в Linux появился в 2.2, затем код был переписан Леннертом Буйтенхеком (Lennert Buytenhek). Код bridge интегрирован в ядра серий 2.4 и 2.6. Железо - Intel Pentum 133 - RAM 32 mb - hdd 1024 mb - 2 сетевые карты 100 Mbps или 1000 Mbps (можно и больше, но желательно одинаковые).

Установка ПО Ставим Linux Debian с минимумом пакетов, сеть не настраиваем. После установки Debian ставим несколько необходимых пакетов:

Код:

# apt-get mc
# apt-get install bridge-utils
# apt-get install iproute
# apt-get install iftop
# apt-get install bmon
# apt-get install openssh-server
# apt-get install iperf

Настройка моста Узнаем где наши сетевые карты Код:

# ifconfig
eth1      Link encap:Ethernet  HWaddr 00:19:5B:88:B2:85
          inet6 addr: fe80::219:5bff:fe88:c287/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:3871824 errors:0 dropped:0 overruns:0 frame:0
          TX packets:4707022 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:1031462268 (983.6 MiB)  TX bytes:1375550080 (1.2 GiB)
          Interrupt:10 Base address:0x6200

eth2      Link encap:Ethernet  HWaddr 00:19:5B:88:C7:86
          inet6 addr: fe80::219:5bff:fe88:c288/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:4707923 errors:0 dropped:0 overruns:0 frame:0
          TX packets:3855788 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:1377378066 (1.2 GiB)  TX bytes:1020322438 (973.0 MiB)
          Interrupt:9 Base address:0x6300

lo        Link encap:Local Loopback
          inet addr:127.0.0.1  Mask:255.0.0.0
          inet6 addr: ::1/128 Scope:Host
          UP LOOPBACK RUNNING  MTU:16436  Metric:1
          RX packets:56 errors:0 dropped:0 overruns:0 frame:0
          TX packets:56 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0
          RX bytes:4396 (4.2 KiB)  TX bytes:4396 (4.2 KiB)

Настройки сети в Linux Debian находятся в файле /etc/network/interfaces У меня на мосте он имеет такой вид: Код:

1. The loopback network interface

auto lo
iface lo inet loopback

Создаём скрипт /etc/network/if-up.d/bridge Код:

#!/bin/sh

1. Чистим настройки от предыдущего запуска скрипта

ifconfig br0 down # Отключаем интерфейс моста
ifconfig eth1 down # Отключаем сетевую карту eth1
ifconfig eth2 down # Отключаем сетевую карту eth2
brctl delbr br0 # Удаляем имя моста

1. Запускаем бридж

brctl addbr br0 # Задаём имя бриджу
brctl addif br0 eth1 # Указываем какие интерфейсы
brctl addif br0 eth2 # работают в режиме моста.

brctl stp br0 off # Отключаем режим STP

# brctl setfd br0 15 # Актуально только при
# brctl setageing br0 60 # использовании STP

1. Задаём IP моста, для дальнейшего управления им через ssh

ifconfig br0 192.168.110.251 netmask 255.255.0.0 broadcast 192.168.255.255

1. Удаляем IP сетевых карт

ifconfig eth1 0.0.0.0
ifconfig eth2 0.0.0.0

1. Поднимаем интерфейсы сетевых карт и моста

ifconfig eth1 up
ifconfig eth2 up
ifconfig br0 up

В принципе мост готов к использованию, надо только перезагрузить компьютер или выполнить скрипт (не забудьте его сделать запускаемым от имени root 774 Код:

# chgrp root /etc/network/if-up.d/bridge
# chown root /etc/network/if-up.d/bridge
# chmod 774 /etc/network/if-up.d/bridge

Настройка маршрутизации

Может возникнуть необходимость указать с какой стороны находится тот или иной компьютер. Дописываем в наш скрипт следующие команды:

1. Сообщаем что ip 192.168.110.200 находится со стороны eth1

Код:

route add -host 192.168.110.200 dev eth1

1. Сообщаем что ip 192.168.88.250 находится со стороны eth2

Код:

route add -host 192.168.88.250 dev eth2

1. Сообщаем мосту с какой стороны сеть 192.168.55.0/24 (255.255.255.0)

Код:

route add -net 192.168.55.0/24 dev eth1

После таких настроек ваш мост станет немного умнее. Теперь для проверки маршрутизации набираем команду: Код:

# route
Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
192.168.110.200 *               255.255.255.255 UH    0      0        0 eth1
192.168.88.250  *               255.255.255.255 UH    0      0        0 eth2
192.168.55.0     *               255.255.255.0     U     0      0        0 eth1
localnet        *               255.255.0.0     U     0      0        0 br0

Удалённое управление мостом

Входим на мост удалённо как пользователь root (под root лучше не работать): Код:

# ssh root@192.168.110.251

Теперь можно работать с мостом как с настольным компьютером в текстовом режиме.

Мониторинг и управление

1. Удобная утилита для просмотра загрузки сети и мостаю

Код:

bmon

1. Ещё не менее полезная утилита мониторинга сети

Код:

iftop -i br0

1. инф. о сетевых интерфейсах

Код:

ifconfig

1. поднять (убить) сетевой интерфейс

Код:

ifconfig eth1 up (down)

1. инф. о мосте

Код:

brctl show

1. таблица MAC-адресов моста

Код:

brctl showmacs br0

1. ARP-таблица

Код:

arp -a

1. Снифер

Код:

tcpdump host 192.168.110.100

---

Выдержка из man: NAME

      bridge-utils-interfaces - bridge-utils extensions for the interfaces(5)
      file format

DESCRIPTION

      /etc/network/interfaces  contains   network   interface   configuration
      information  for  the  ifup(8)  and  ifdown(8)  commands.  This manpage
      describes the bridge extensions  to  the  standard  interfaces(5)  file
      format.

      The  main  extension  is  the bridge_ports option, with it you describe
      that the interface is a bridge and what ports does it have. These ports
      are the interfaces that are part of the bridge, and they shouldn't have
      any stanzas defining them on  the  interfaces  file.  Other  extensions
      allow you to tune the bridge options or change a bridge behaviour.

      We'll see this with an example:
      auto br0
      iface br0 inet static
          address 192.168.1.2
          network 192.168.1.0
          netmask 255.255.255.0
          broadcast 192.168.1.255
          gateway 192.168.1.1
          bridge_ports all
      Well,  after  setting this, an ifup br0, or the next reboot, should let
      you have a bridge up and running, after waiting for the ports to get to
      the  forwarding  status,  of course. This bridge will be using all your
      ethX interfaces, as we have stated on the bridge_ports line.

      The Debian bridge setup scripts will wait for it to get ready to  work.
      They  do  this by trying to guess the maximum time that the bridge will
      need to get to the forwarding status, and by default,  they  will  wait
      for  the  bridge  to get there, or for the estimated maximum time to go
      by.  This is done so that the services that are loaded after the bridge
      setup  have  a  working  network  interface  and don't fail because the
      bridge is still not working. See bridge_maxwait if you want  to  change
      this behaviour.

      An  example  of  how  to  setup  a so called anonymous bridge (a bridge
      without an assigned IP) would look like this:
      iface br1 inet manual
           bridge_ports eth1 eth2
           bridge_maxwait 0
      Here we select the interfaces eth1 and eth2 to be added to  the  bridge
      interface  br1,  which  will  be  an anonymous bridge, we also tell the
      scripts not to wait, as we won't be having any service running on  that
      interface (it doesn't even have an IP).

      An example of a little more complex bridge setup could be:
      auto br0
      iface br0 inet static
          address 192.168.1.2
          network 192.168.1.0
          netmask 255.255.255.0
          broadcast 192.168.1.255
          bridge_ports all weird0
          bridge_bridgeprio 32767
          bridge_portprio eth0 129
          bridge_fd 5
      In  this  example we select all the eth* devices plus a weird device to
      be added to the bridge, also we change the bridge default priority to a
      higher  one  so  that  this  bridge  becomes  the root (if there are no
      bridges with higher priority on the net, that is)  and  also  we  lower
      priority  of  port eth0 so that it is not used if there are other ports
      with higher priority to reach the same destination, at the end we lower
      the default forward delay.

      If there is a need to set up any of the interfaces participating on the
      bridge and not the bridge itself, then we must add the commands to  set
      up  those  settings in a "pre-up" or "up" statement. This means that if
      we have a wireless card that we want to add to a bridge and we want  to
      set  it  to  master, and select the essid, instead of using the typical
      wireless_* commands we could add to  the  bridge  definition  something
      like this:
      pre-up iwconfig wlan0 mode master essid myESSID
      Be aware, however, that using wireless cards as part of a bridge is not
      a good idea if the card belonging to the bridge  is  in  managed  mode.
      Trying  to bridge packets coming out of our LAN through a wireless card
      that is set in managed mode (the card is a client of an AP) is bound to
      give  problems,  as the AP will probably refuse packets with source MAC
      addresses which are not associated (this will  be  the  case  of  other
      machines going through the wireless card of the bridge into the AP).

      Multiple stanzas of a bridge definition are currently not supported, so
      if you want to add a ipv6 and a ipv4 to a  bridge  do  it  all  in  one
      definition  by  using the "up" option. If however you still want to use
      multiple stanzas or would like to read more on this bug you can see  it
      at http://bugs.debian.org/319832

IFACE OPTIONS

      A   little  explanation  on  the  new  options  that  can  be  used  on
      /etc/network/interfaces to setup the bridge, so you don't  have  to  go
      and look at the scripts...

      bridge_ports interface specification
             this option must exist for the scripts to setup the bridge, with
             it you specify the ports you want to add to your bridge,  either
             using  "none" if you want a bridge without any interfaces or you
             want to add them later using brctl, or a list of the  interfaces
             you want to add separated by spaces, for example:
             bridge_ports eth0 eth4
             You  should  not  put any lines to configure the interfaces that
             will be used by the bridge, as this will be setup  automatically
             by the scripts when bringing the bridge up.

             If you need to specify the interfaces more flexibly, you can use
             the following syntax (most useful on a Xen dom0):
             bridge_ports regex (eth|vif).*
             This means to evaluate (as in  egrep(1))  the  expressions  that
             follow  after  "regex"  until  either  the  end  or  a "noregex"
             statement is reached.  The  regular  expressions  are  evaluated
             against all local interfaces and those that match are added.

             Specifying  "all"  is  short  for  "regex  eth.*  em.*  p[0-9].*
             noregex" and will get all the ethX and  biosdevname-format  (emX
             and pX) interfaces added to the bridge.

             Carrying this to the extremes, the following is valid syntax:
             bridge_ports all regex if.0 noregex ext0 regex vif.*
             This will add all ethX interfaces, the ifX0 interfaces, the ext0
             interface and all vifX interfaces.

      bridge_ageing time
             set ageing time, default is 300, can have a fractional part.

      bridge_bridgeprio priority
             set bridge priority, priority is between 0 and 65535, default is
             32768,  affects  bridge  id,  lowest priority bridge will be the
             root.

      bridge_fd time
             set bridge forward delay to time seconds,  default  is  15,  can
             have a fractional part.

      bridge_gcint time
             set  garbage  collection interval to time seconds, default is 4,
             can have a fractional part.

      bridge_hello time
             set hello time to  time  seconds,  default  is  2,  can  have  a
             fractional part.

      bridge_hw MAC address
             set the Ethernet MAC address of all the bridge interfaces to the
             specified one so that the bridge ends up  having  this  hardware
             address as well. WARNING: use this only if you know what you are
             doing, changing the MAC address of the cards may  cause  trouble
             if  you  don't  know  what  you are doing. To see the discussion
             about this feature and the problems that can cause you  can  try
             to  have  a look at the bug that asked for this feature visiting
             http://bugs.debian.org/271406

      bridge_maxage time
             set max message age to time seconds, default is 20, can  have  a
             fractional part.

      bridge_maxwait time
             forces  to  time seconds the maximum time that the Debian bridge
             setup scripts will wait for the  bridge  ports  to  get  to  the
             forwarding  status, doesn't allow factional part. If it is equal
             to 0 then no waiting is done.

      bridge_pathcost port cost
             set path cost for a port, default is 100, port is  the  name  of
             the interface to which this setting applies.

      bridge_portprio port priority
             set  port priority, default is 128, affects port id, port is the
             name of the interface to which this setting applies.

      bridge_stp state
             turn spanning tree protocol on/off, state values are on  or  yes
             to  turn  stp  on and any other thing to set it off, default has
             changed to off for security reasons in latest  kernels,  so  you
             should  specify  if you want stp on or off with this option, and
             not rely on your kernel's default behaviour.

      bridge_waitport time [ports]
             wait for a max of time seconds for the specified ports to become
             available,  if  no  ports  are specified then those specified on
             bridge_ports will be used here. Specifying no ports here  should
             not  be  used if we are using regex or "all" on bridge_ports, as
             it wouldn't work.

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Источники:

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• man brige
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