Параметры ядра Linux:Networking:TCP

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TCP/IP networking

TCP/IP networking
These are the protocols used on the Internet and on most local Ethernets. It is highly recommended to say Y here (this will enlarge your kernel by about 144 KB), since some programs (e.g. the X window system) use TCP/IP even if your machine is not connected to any other computer. You will get the so-called loopback device which allows you to ping yourself (great fun, that!).

For an excellent introduction to Linux networking, please read the Linux Networking HOWTO, available from <http://www.tldp.org/docs.html#howto>.

If you say Y here and also to "/proc file system support" and "Sysctl support" below, you can change various aspects of the behavior of the TCP/IP code by writing to the (virtual) files in /proc/sys/net/ipv4/*; the options are explained in the file <file:Documentation/networking/ip-sysctl.txt>.

Short answer: say Y.

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Поддержка протоколов TCP/IP

Протоколы TCP/IP используются в Internet и в большинстве локальных сетей Ethernet. Настоятельно рекомендуется указать Y (это увеличит размер ядра примерно на 144 КБ), дело в том, что некоторые программы (например, X Window system) используют TCP/IP, даже если компьютер не подключён к сети. Вы будете использовать сетевое устройство loopback, которое позволяет пинговать самого себя (хорошая шутка).

Для общего введения в сети Linux, пожалуйста, прочитайте руководство Linux Networking HOWTO, которое доступно на <http://www.tldp.org/docs.html#howto>.

Если вы выберите Y здесь, а также «/proc file system support» и «Sysctl support» ниже, то вы сможете изменять поведение TCP/IP путём записи в (виртуальные) файлы в /proc/sys/net/ipv4/*; настройки описаны в файле <file:Documentation/networking/ip-sysctl.txt>.

Маленькая подсказка: выберите Y.

  IP: multicasting
  This is code for addressing several networked computers at once, enlarging your kernel by about 2 KB. You need multicasting if you intend to participate in the MBONE, a high bandwidth network on top of the Internet which carries audio and video broadcasts. More information about the MBONE is on the WWW at <http://www-itg.lbl.gov/mbone/>. Information about the multicast capabilities of the various network cards is contained in <file:Documentation/networking/multicast.txt>. For most people, it's safe to say N.
 
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Поддержка многоадресной передачи

Многоадресная передача используется при одновременном обращение к нескольким объединенным в сеть компьютерам; её поддержка увеличит размер ядра примерно на 2 КБ. Поддержка многоадресной передачи потребуется, если вы намереваетесь состоять в MBONE, широковещательной многоадресной магистрали, — части Интернета, поддерживающей аудио- и видеоконференции. Более подробную информацию о MBONE можно найти на ресурсе <http://www-itg.lbl.gov/mbone/>. Возможности многоадресной передачи различных сетевых адаптеров описаны в файле Documentation/networking/multicast.txt. В большинстве случаев можно с уверенностью выбрать N (Нет).

  IP: advanced router
  If you intend to run your Linux box mostly as a router, i.e. as a computer that forwards and redistributes network packets, say Y; you will then be presented with several options that allow more precise control about the routing process.

The answer to this question won't directly affect the kernel: answering N will just cause the configurator to skip all the questions about advanced routing.

Note that your box can only act as a router if you enable IP forwarding in your kernel; you can do that by saying Y to "/proc file system support" and "Sysctl support" below and executing the line

echo "1" > /proc/sys/net/ipv4/ip_forward

at boot time after the /proc file system has been mounted. If you turn on IP forwarding, you will also get the rp_filter, which automatically rejects incoming packets if the routing table entry for their source address doesn't match the network interface they're arriving on. This has security advantages because it prevents the so-called IP spoofing, however it can pose problems if you use asymmetric routing (packets from you to a host take a different path than packets from that host to you) or if you operate a non-routing host which has several IP addresses on different interfaces. To turn rp_filter off use:

echo 0 > /proc/sys/net/ipv4/conf/<device>/rp_filter

or

echo 0 > /proc/sys/net/ipv4/conf/all/rp_filter

If unsure, say N here.

 
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IP: Расширенные настройки маршрутизации

Если вы собираетесь использовать вашу систему в основном в качестве маршрутизатора, то есть компьютера, который передаёт и перераспределяет сетевые пакеты, выберите Y. В этом случае вам станут доступны дополнительные опции для более детальной настройки процесса маршрутизации.

Данная опция напрямую на ядро не влияет. Если вы выберите N, то конфигуратор просто пропустит вопросы о детальной настройке процесса маршрутизации.

Заметьте также, что ваша система сможет выступать в роли маршрутизатора только в том случае, если вы разрешите IP-маршрутизацию в ядре, это можно сделать, выбрав Y напротив опции «Поддержка файловой системы /proc» и опции «Поддержка Sysctl», а также выполнив следующую строку:

echo "1" > /proc/sys/net/ipv4/ip_forward

во время процесса загрузки, но только после того, как файловая система /proc была смонтирована. В случае включения IP-маршрутизации также включится rp_filter, который автоматически отклоняет входящие пакеты в том случае, если запись в таблице маршрутизации для их исходного адреса не соответствует сетевому интерфейсу, с которого они прибыли. Такое поведение имеет преимущества в плане безопасности потому, что предотвращает так называемый IP spoofing (подмену IP-адреса), однако оно также может принести некоторые проблемы, в том случае, если вы используете ассиметричную маршрутизацию (пакеты от вас до определенного сетевого узла проходят по иному пути, чем пакеты от этого узла к вам) или если вы работаете на сетевом узле без маршрутизации, который имеет несколько IP-адресов на разных интерфейсах. Для выключения rp_filter воспользуйтесь следующей командой:

echo 0 > /proc/sys/net/ipv4/conf/<device>/rp_filter

или

echo 0 > /proc/sys/net/ipv4/conf/all/rp_filter

Если не уверены, выбирайте N.

    Choose IP: FIB lookup algoritm (choose FIB_HASH if unsare)
    There is no help available for this kernel option.
   
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      FIB_HASH
      Current FIB is very proven and good enough for most users.
     
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      FIB_TRIE
      Use new experimental LC-trie as FIB lookup algorithm. This improves lookup performance if you have a large number of routes.

LC-trie is a longest matching prefix lookup algorithm whichя performs better than FIB_HASH for large routing tables. But, it consumes more memory and is more complex.

LC-trie is described in:

IP-address lookup using LC-tries. Stefan Nilsson and Gunnar Karlsson IEEE Journal on Selected Areas in Communications, 17(6):1083-1092, June 1999 An experimental study of compression methods for dynamic tries Stefan Nilsson and Matti Tikkanen. Algorithmica, 33(1):19-33, 2002. http://www.nada.kth.se/~snilsson/public/papers/dyntrie2/

     
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  IP: policy routing
  Normally, a router decides what to do with a received packet based solely on the packet's final destination address. If you say Y here, the Linux router will also be able to take the packet's source address into account. Furthermore, the TOS (Type-Of-Service) field of the packet can be used for routing decisions as well.

If you are interested in this, please see the preliminary documentation at <http://www.compendium.com.ar/policy-routing.txt> and <ftp://post.tepkom.ru/pub/vol2/Linux/docs/advanced-routing.tex>. You will need supporting software from <ftp://ftp.tux.org/pub/net/ip-routing/>.

If unsure, say N.

 
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  IP: equal cost multipath
  Normally, the routing tables specify a single action to be taken in a deterministic manner for a given packet. If you say Y here however, it becomes possible to attach several actions to a packet pattern, in effect specifying several alternative paths to travel for those packets. The router considers all these paths to be of equal "cost" and chooses one of them in a non-deterministic fashion if a matching packet arrives.
 
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    IP: equal cost multipath with caching support
    Normally, equal cost multipath routing is not supported by the routing cache. If you say Y here, alternative routes are cached and on cache lookup a route is chosen in a configurable fashion.

If unsure, say N.

   
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      MULTIPATH: round robin algorithm
      Mulitpath routes are chosen according to Round Robin
     
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      MULTIPATH: random algorithm
      Multipath routes are chosen in a random fashion. Actually, there is no weight for a route. The advantage of this policy is that it is implemented stateless and therefore introduces only a very small delay.
     
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      MULTIPATH: weighted random algorithm
      Multipath routes are chosen in a weighted random fashion. The per route weights are the weights visible via ip route 2. As the corresponding state management introduces some overhead routing delay is increased.
     
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      MULTIPATH: interface round robin algorithm
      Connections are distributed in a round robin fashion over the available interfaces. This policy makes sense if the connections should be primarily distributed on interfaces and not on routes.
     
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  IP: verbose route monitoring
  If you say Y here, which is recommended, then the kernel will print verbose messages regarding the routing, for example warnings about received packets which look strange and could be evidence of an attack or a misconfigured system somewhere. The information is handled by the klogd daemon which is responsible for kernel messages ("man klogd").
 
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Если, как это рекомендуется, вы выберите Y, ядро начнет выдавать подробные сообщения, посвящённые роутингу. Например, предупреждения о получении пакетов, которые странно выглядят и могут служить доказательством попытки атаки на систему или говорят о том, что ваша система где-то неправильно сконфигурирована. Информация посылается через демон klogd (man klogd).
  IP: kernel level autocinfiguration
  This enables automatic configuration of IP addresses of devices and of the routing table during kernel boot, based on either information supplied on the kernel command line or by BOOTP or RARP protocols. You need to say Y only for diskless machines requiring network access to boot (in which case you want to say Y to "Root file system on NFS" as well), because all other machines configure the network in their startup scripts.
 
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Этот параметр включает автоматическую конфигурацию сетевых устройств (IP-адрес и т.д.) и таблицы маршрутизации во время загрузки ядра. Информация о конфигурации может быть получена из командной строки ядра или по протоколам BOOTP, RARP или DHCP. Вы должны включать этот параметр только для бездисковых рабочих станций, которым необходим доступ к сети во время загрузки (например, в случае когда был выбран параметр «Root file system on NFS»). На всех остальных машинах конфигурация сети происходит в стартовых скриптах.
    IP: DHCP support
    If you want your Linux box to mount its whole root file system (the one containing the directory /) from some other computer over the net via NFS and you want the IP address of your computer to be discovered automatically at boot time using the DHCP protocol (a special protocol designed for doing this job), say Y here. In case the boot ROM of your network card was designed for booting Linux and does DHCP itself, providing all necessary information on the kernel command line, you can say N here.

If unsure, say Y. Note that if you want to use DHCP, a DHCP server must be operating on your network. Read <file:Documentation/nfsroot.txt> for details.

   
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Поддержка протокола DHCP

Если вы хотите, чтобы ваш компьютер, работающий под Linux, монтировал корневую файловую систему с другого компьютера по сети, используя файловую систему NFS, и вы хотите, чтобы при этом IP-адрес вашему компьютеру назначался автоматически во время загрузки, используя протокол DHCP (протокол, разработанный специально для этой цели), то включите эту опцию. В том случае, если загрузочное ПЗУ вашей сетевой карты поддерживает DHCP и способно загрузить Linux и передать ему все необходимые параметры в командной строке ядра, то от использования данной опции можно отказаться.

Включите эту опцию, если вас гложут сомнения. Учтите, что для использования DHCP в вашей сети необходимо завести DHCP-сервер. Подробности настройка Linux для монтирования корневой файловой системы по сети описаны в файле <file:Documentation/nfsroot.txt>.

    IP: BOOTP support
    If you want your Linux box to mount its whole root file system (the one containing the directory /) from some other computer over the net via NFS and you want the IP address of your computer to be discovered automatically at boot time using the BOOTP protocol (a special protocol designed for doing this job), say Y here. In case the boot ROM of your network card was designed for booting Linux and does BOOTP itself, providing all necessary information on the kernel command line, you can say N here. If unsure, say Y. Note that if you want to use BOOTP, a BOOTP server must be operating on your network. Read <file:Documentation/nfsroot.txt> for details.
   
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Поддержка протокола BOOTP

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    IP: RARP support
    If you want your Linux box to mount its whole root file system (the one containing the directory /) from some other computer over the net via NFS and you want the IP address of your computer to be discovered automatically at boot time using the RARP protocol (an older protocol which is being obsoleted by BOOTP and DHCP), say Y here. Note that if you want to use RARP, a RARP server must be operating on your network. Read <file:Documentation/nfsroot.txt> for details.
   
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Поддержка протокола RARP

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  IP: tunneling
  Tunneling means encapsulating data of one protocol type within another protocol and sending it over a channel that understands the encapsulating protocol. This particular tunneling driver implements encapsulation of IP within IP, which sounds kind of pointless, but can be useful if you want to make your (or some other) machine appear on a different network than it physically is, or to use mobile-IP facilities (allowing laptops to seamlessly move between networks without changing their IP addresses).

Saying Y to this option will produce two modules ( = code which can be inserted in and removed from the running kernel whenever you want). Most people won't need this and can say N.

 
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  IP: GRE tunnels over IP
  Tunneling means encapsulating data of one protocol type within another protocol and sending it over a channel that understands the encapsulating protocol. This particular tunneling driver implements GRE (Generic Routing Encapsulation) and at this time allows encapsulating of IPv4 or IPv6 over existing IPv4 infrastructure. This driver is useful if the other endpoint is a Cisco router: Cisco likes GRE much better than the other Linux tunneling driver ("IP tunneling" above). In addition, GRE allows multicast redistribution through the tunnel.
 
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    IP: broadcast GRE over IP
    IP: multicast routing
   
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One application of GRE/IP is to construct a broadcast WAN (Wide Area Network), which looks like a normal Ethernet LAN (Local Area Network), but can be distributed all over the Internet. If you want to do that, say Y here and to "IP multicast routing" below.
  IP: multicast routing
  This is used if you want your machine to act as a router for IP packets that have several destination addresses. It is needed on the MBONE, a high bandwidth network on top of the Internet which carries audio and video broadcasts. In order to do that, you would most likely run the program mrouted. Information about the multicast capabilities of the various network cards is contained in <file:Documentation/networking/multicast.txt>. If you haven't heard about it, you don't need it.
 
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    IP: PIM-SM version 1 support
    Kernel side support for Sparse Mode PIM (Protocol Independent Multicast) version 1. This multicast routing protocol is used widely because Cisco supports it. You need special software to use it (pimd-v1). Please see <http://netweb.usc.edu/pim/> for more information about PIM.

Say Y if you want to use PIM-SM v1. Note that you can say N here if you just want to use Dense Mode PIM.

   
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    IP: PIM-SM version 2 support
    Kernel side support for Sparse Mode PIM version 2. In order to use this, you need an experimental routing daemon supporting it (pimd or gated-5). This routing protocol is not used widely, so say N unless you want to play with it.
   
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  ARP daemin support[EXPERIMENTAL]
  Normally, the kernel maintains an internal cache which maps IP addresses to hardware addresses on the local network, so that Ethernet/Token Ring/ etc. frames are sent to the proper address on the physical networking layer. For small networks having a few hundred directly connected hosts or less, keeping this address resolution (ARP) cache inside the kernel works well. However, maintaining an internal ARP cache does not work well for very large switched networks, and will use a lot of kernel memory if TCP/IP connections are made to many machines on the network.

If you say Y here, the kernel's internal ARP cache will never grow to more than 256 entries (the oldest entries are expired in a LIFO manner) and communication will be attempted with the user space ARP daemon arpd. Arpd then answers the address resolution request either from its own cache or by asking the net.

This code is experimental and also obsolete. If you want to use it, you need to find a version of the daemon arpd on the net somewhere, and you should also say Y to "Kernel/User network link driver", below. If unsure, say N.

 
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  TCP syncookie support (disable per default)
  Normal TCP/IP networking is open to an attack known as "SYN flooding". This denial-of-service attack prevents legitimate remote users from being able to connect to your computer during an ongoing attack and requires very little work from the attacker, who can operate from anywhere on the Internet.

SYN cookies provide protection against this type of attack. If you say Y here, the TCP/IP stack will use a cryptographic challenge protocol known as "SYN cookies" to enable legitimate users to continue to connect, even when your machine is under attack. There is no need for the legitimate users to change their TCP/IP software; SYN cookies work transparently to them. For technical information about SYN cookies, check out <http://cr.yp.to/syncookies.html>.

If you are SYN flooded, the source address reported by the kernel is likely to have been forged by the attacker; it is only reported as an aid in tracing the packets to their actual source and should not be taken as absolute truth.

SYN cookies may prevent correct error reporting on clients when the server is really overloaded. If this happens frequently better turn them off.

If you say Y here, note that SYN cookies aren't enabled by default; you can enable them by saying Y to "/proc file system support" and "Sysctl support" below and executing the command

echo 1 >/proc/sys/net/ipv4/tcp_syncookies

at boot time after the /proc file system has been mounted.

If unsure, say N.

 
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  IP: AH transformation
  Support for IPsec AH.

If unsure, say Y.

 
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  IP: ESP transformation
  Support for IPsec ESP.

If unsure, say Y.

 
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  IP: IPcomp transformation
  Support for IP Payload Compression Protocol (IPComp) (RFC3173), typically needed for IPsec.

If unsure, say Y.

 
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  IP: IPsec transport mode
  Support for IPsec transport mode.

If unsure, say Y.

 
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  IP: IPsec tunnel mode
  Support for IPsec tunnel mode.

If unsure, say Y.

 
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  IP: IPsec BEET mode
  Support for IPsec BEET mode.

If unsure, say Y.

 
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  INET: socket monitoring interface
  Support for INET (TCP, DCCP, etc) socket monitoring interface used by native Linux tools such as ss. ss is included in iproute2, currently downloadable at <http://developer.osdl.org/dev/iproute2>.

If unsure, say Y.

 
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