Dhcpcd

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خطا در ایجاد بندانگشتی: نمی‌توان تصویر بندانگشتی را در مقصد ذخیره کرد

یادداشت: این صفحه نیاز به ترجمه دارد. (در بحث:Dhcpcd# در این مورد تبادل نظر کنید.)

dhcpcd یک کلاینت برای DHCP و DHCPv6 است. این کلاینت هم‌اکنون بیشترین امکانات را در در میان کلاینت‌های متن‌باز DHCP دارد. برای دیدن فهرست امکانات آن این پیوند را ببینید.

نکته: dhcpcd (منظور دیمون کلاینت DHCP) همان dhcpd (منظور دیمون سرور DHCP) نیست.

نصب

بسته dhcpcd بخشی از مجموعه بسته های base میباشد، پس به احتمال زیاد این بسته هم‌اکنون بر روی سیستم شما نصب میباشد

dhcpcd-uiAUR یک رابط گرافیکی ساخته شده بر پایه GTK+ برای دیمون dhcpcd بوده که میتوانید از طریق مخزن AUR به نصب ان اقدام نمایید. این رابط به شما اجازه انتخاب و اعمال رمز عبور برای برای یک شبکه بدون سیم را میدهد.

اجرا

برای فعال کردن این دیمون بر روی تمامی رابط های ارتباطی شبکه سرویس ‎dhcpcd.service‎ را اجرا یا فعال نمایید.

برای فعال کردن این سرویس بر روی رابط خاص به شکل ‎dhcpcd@interface.service‎ عمل نمایید.

یا برای اجرای این سرویس به صورت دستی از دستور زیر استفاده نمایید.

# dhcpcd interface

در تمامی مراحل بالا به سیستم شما یک ادرس آی پی متغییر تعلق میگیرد. اگر خواهان ادرس آی پی ایستا(static) هستید #Static profile را مشاهده کنید.

تنظیمات

تنظیمات اصلی در فایل ‎/etc/dhcpcd.conf‎ انجام میگیرد. جهت اطلاعات بیشتر به dhcpcd.conf(5) مراجعه کنید. در پایین به برخی از پر استفاده ترین تنظیمات میپردازیم.

مسیر ایستای DHCP

اگر نیاز به یک مسیر ایستای سمت کلاینت دارید، دستور زیر را به ‎/etc/dhcpcd.exit-hook‎ اضافه کنید. مثال زیر یک هوک-اسکریپت رادنشان می‌دهد که یک مسیر ایستا به یک VPN subnet در ‎10.11.12.0/24‎ توسط یک gateway در ‎192.168.192.5‎ اضافه می‌کند:

/etc/dhcpcd.exit-hook
ip route add 10.11.12.0/24 via 192.168.192.5

همچنین می‌توانید چندین مسیر به این پرونده اضافه کنید.

DHCP Client Identifier

The DHCP client may be uniquely identified in different ways by the server:

  1. hostname (or the hostname value sent by the client),
  2. MAC address of the network interface controller through which the connection is being made, linked to this is the third,
  3. Identity Association ID (IAID), which is an abstraction layer to differentiate different use-cases and/or interfaces on a single host,
  4. DHCP Unique Identifier (DUID).

For a further description, see RFC 3315.

It depends on the DHCP-server configuration which options are optional or required to request a DHCP IP lease.

توجه: The dhcpcd default configuration should be sufficient usually. The listed identifiers are determined automatically and manual configuration changes only be required in case of problems.

If the dhcpcd default configuration fails to obtain an IP, the following options are available to use in ‎dhcpcd.conf‎:

  • ‎hostname‎ sends the hostname set in ‎/etc/hostname‎
  • ‎clientid‎ sends the MAC address as identifier
  • ‎iaid <interface>‎ derives the IAID to use for DHCP discovery. It has to be used in an interface block (started by ‎interface <interface>‎, see [۱]), but more frequently the next option is used:
  • ‎duid‎ triggers using a combination of DUID and IAID as identifier.

The DUID value is set in ‎/var/lib/dhcpcd/duid‎. For efficient DHCP lease operation it is important that it is unique for the system and applies to all network interfaces alike, while the IAID represents an identifier for each of the systems' interfaces (see RFC 4361).

Care must be taken on a network running Dynamic DNS to ensure that all three IDs are unique. If duplicate DUID values are presented to the DNS server, e.g. in the case where a virtual machine has been cloned and the hostname and MAC have been made unique but the DUID has not been changed, then the result will be that as each client with the duplicated DUID requests a lease the server will remove the predecessor from the DNS record.

Static profile

Required settings are explained in Network configuration. These typically include the network interface name, IP address, router address, and name server.

Configure a static profile for dhcpcd in ‎/etc/dhcpcd.conf‎, for example:

/etc/dhcpcd.conf
interface eth0
static ip_address=192.168.0.10/24	
static routers=192.168.0.1
static domain_name_servers=192.168.0.1 8.8.8.8

More complicated configurations are possible, for example combining with the ‎arping‎ option. See dhcpcd.conf(5) for details.

Fallback profile

It is possible to configure a static profile within dhcpcd and fall back to it when DHCP lease fails. This is useful particularly for headless machines, where the static profile can be used as "recovery" profile to ensure that it is always possible to connect to the machine.

The following example configures a ‎static_eth0‎ profile with ‎192.168.1.23‎ as IP address, ‎192.168.1.1‎ as gateway and name server, and makes this profile fallback for interface ‎eth0‎.

/etc/dhcpcd.conf
# define static profile
profile static_eth0
static ip_address=192.168.1.23/24
static routers=192.168.1.1
static domain_name_servers=192.168.1.1

# fallback to static profile on eth0
interface eth0
fallback static_eth0

Hooks

dhcpcd executes all scripts found in ‎/usr/lib/dhcpcd/dhcpcd-hooks/‎ in a lexical order. See dhcpcd.conf(5) and dhcpcd-run-hooks(8) for details.

توجه:
  • Each script can be disabled using the ‎nohook‎ option in ‎dhcpcd.conf‎.
  • The ‎env‎ option can be used to set an environment variable for all hooks. For example, you can force the hostname hook to always set the hostname with ‎env force_hostname=YES‎.

خطا در ایجاد بندانگشتی: نمی‌توان تصویر بندانگشتی را در مقصد ذخیره کرد
This article or section needs expansion.
خطا در ایجاد بندانگشتی: نمی‌توان تصویر بندانگشتی را در مقصد ذخیره کرد

Reason: describe (at least some) provided hooks. (Discuss in بحث:Dhcpcd#)

10-wpa_supplicant

Enable this hook by creating a symbolic link (to ensure that always the current version is used, even after package updates):

# ln -s /usr/share/dhcpcd/hooks/10-wpa_supplicant /usr/lib/dhcpcd/dhcpcd-hooks/

The ‎10-wpa_supplicant‎ hook, if enabled, automatically launches WPA supplicant on wireless interfaces. It is started only if:

  • no wpa_supplicant process is already listening on that interface.
  • a wpa_supplicant configuration file exists. dhcpcd checks
/etc/wpa_supplicant/wpa_supplicant-interface.conf
/etc/wpa_supplicant/wpa_supplicant.conf
/etc/wpa_supplicant-interface.conf
/etc/wpa_supplicant.conf

by default, in that order, but a custom path can be set by adding ‎env wpa_supplicant_conf=configuration_file_path into ‎/etc/dhcpcd.conf‎.

توجه: The hook stops at the first configuration file found, thus you should take this into consideration if you have several wpa_supplicant configuration files, otherwise dhcpcd might end up using the wrong file.

If you manage wireless connections with wpa_supplicant itself, the hook may create unwanted connection events. For example, if you stop wpa_supplicant the hook may bring the interface up again. Also, if you use netctl-auto, wpa_supplicant is started automatically with ‎/run/network/wpa_supplicant_interface.conf‎ for config, so starting it again from the hook is unnecessary and may result in boot-time parse errors of the ‎/etc/wpa_supplicant/wpa_supplicant.conf‎ file, which only contains dummy values in the default packaged version.

To disable the hook, add ‎nohook wpa_supplicant‎ to ‎dhcpcd.conf‎.

Tips and tricks

Speed up DHCP by disabling ARP probing

dhcpcd contains an implementation of a recommendation of the DHCP standard (RFC2131 section 2.2) to check via ARP if the assigned IP address is really not taken. This seems mostly useless in home networks, so you can save about 5 seconds on every connect by adding the following line to ‎/etc/dhcpcd.conf‎:

noarp

This is equivalent to passing ‎--noarp‎ to ‎dhcpcd‎, and disables the described ARP probing, speeding up connections to networks with DHCP.

Remove old DHCP lease

The file ‎/var/lib/dhcpcd/interface.lease‎, where interface is the name of the interface on which you have a lease, contains the actual DHCP lease reply sent by the DHCP server. For a wireless interface, the filename is ‎/var/lib/dhcpcd/interface-ssid.lease‎, where ssid is the name of the wireless network. It is used to determine the last lease from the server, and its ‎mtime‎ attribute is used to determine when it was issued. This last lease information is then used to request the same IP address previously held on a network, if it is available. If you do not want that, simply delete this file.

If the DHCP server still assigns the same IP address, this may happen because it is configured to keep the assignment stable and recognizes the requesting DHCP client id or DUID (see #DHCP Client Identifier). You can test it by stopping dhcpcd and removing or renaming ‎/var/lib/dhcpcd/duid‎. dhcpcd will generate a new one on next run.

Keep in mind that the DUID is intended as persistent machine identifier across reboots and interfaces. If you are transferring the system to new computer, preserving this file should make it appear as old one.

Different IPs when multi-booting

If you are dualbooting Arch and OS X or Windows and want each to receive different IP addresses, you can exert control about the IPs leased by specifying a different DUID in each operating system installation.

In Windows (post XP) the DUID should be stored in the

\HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip6\Parameters\Dhcpv6DUID 

registry key.

On OS X it is directly accessible in ‎Network\adapter\dhcp preferences panel‎.

If you are using a dnsmasq DHCP server, the different DUIDs can be used in appropriate ‎dhcp-host=‎ rules in its configuration.

resolv.conf

dhcpcd' by default overwrites resolv.conf.

This can be stopped by adding the following to the last section of ‎/etc/dhcpcd.conf‎:

nohook resolv.conf

Alternatively, you can create a file called ‎/etc/resolv.conf.head‎ containing your DNS servers. dhcpcd will prepend this file to the beginning of ‎/etc/resolv.conf‎.

Or you can configure dhcpcd to use the same DNS servers every time. To do this, add the following line at the end of your ‎/etc/dhcpcd.conf‎, where dns-server-ip-addressses is a space separated list of DNS IP addresses.

static domain_name_servers=dns-server-ip-addresses

For example, to set it to Google's DNS servers:

static domain_name_servers=8.8.8.8 8.8.4.4

Troubleshooting

Client ID

If you are on a network with DHCPv4 that filters Client IDs based on MAC addresses, you may need to change the following line:

/etc/dhcpcd.conf
# Use the same DUID + IAID as set in DHCPv6 for DHCPv4 Client ID as per RFC4361. 
duid

To:

/etc/dhcpcd.conf
# Use the hardware address of the interface for the Client ID (DHCPv4).
clientid

Else, you may not obtain a lease since the DHCP server may not read your DHCPv6-style Client ID correctly. See RFC 4361 for more information.

Check DHCP problem by releasing IP first

A problem may occur when DHCP gets a wrong IP assignment, such as when two routers are tied together through a VPN. The router that is connected through the VPN may be assigning IP address. To fix it, as root, release the IP address:

# dhcpcd -k

Then request a new one:

# dhcpcd

You may have to run those two commands many times.

Problems with noncompliant routers

For some (noncompliant) routers, you will not be able to connect properly unless you comment the line

require dhcp_server_identifier

in ‎/etc/dhcpcd.conf‎. This should not cause issues unless you have multiple DHCP servers on your network (not typical); see this page for more information.

dhcpcd and systemd network interfaces

‎dhcpcd.service‎ can be enabled without specifying an interface. This may, however, create a race condition at boot with systemd-udevd trying to apply a predictable network interface name:

error changing net interface name wlan0 to wlp4s0: Device or resource busy" 

To avoid it, enable dhcpcd per interface it should bind to as described in #Running. The downside of the template unit is, however, that it does not support hot-plugging of a wired connection and will fail if the network cable is not connected. To work-around the failure, see #Timeout delay.

It is also possible to use ‎denyinterfaces‎ or ‎allowinterfaces‎ in dhcpcd.conf(5) to stop dhcpcd from binding to kernel names, for example

denyinterfaces wlan* eth*

Timeout delay

If dhcpcd operates on a single interface and fails to obtain a lease after 30 seconds (for example when the server is not ready or the cable not plugged), it will exit with an error.

To have dhcpcd wait indefinitely for one-time, edit the unit and set the ‎timeout‎ option to ‎0‎:

/etc/systemd/system/dhcpcd@.service.d/timeout.conf
[Service]
ExecStart=
ExecStart=/usr/bin/dhcpcd -w -q -t 0 %I

To have it wait indefinitely, let the unit restart after it exited:

/etc/systemd/system/dhcpcd@.service.d/dhcpcdrestart.conf
[Service]
Restart=always

Known issues

dhcpcd@.service causes slow startup

By default the ‎dhcpcd@.service‎ waits to get an IP address before forking into the background via the ‎-w‎ flag for dhcpcd. If the unit is enabled, this may cause the boot to wait for an IP address before continuing. To fix this, create a drop-in file for the unit with the following:

/etc/systemd/system/dhcpcd@.service.d/no-wait.conf
[Service]
ExecStart=
ExecStart=/usr/bin/dhcpcd -b -q %I

See also FS#49685.

dhcpcd does not remove IP address from interface on release

خطا در ایجاد بندانگشتی: نمی‌توان تصویر بندانگشتی را در مقصد ذخیره کرد
این قسمت برای حذف مطرح شده است.
خطا در ایجاد بندانگشتی: نمی‌توان تصویر بندانگشتی را در مقصد ذخیره کرد

دلیل: Bug was fixed. (در بحث:Dhcpcd# در این مورد تبادل نظر کنید.)

The issue is described in https://roy.marples.name/archives/dhcpcd-discuss/0002131.html. It is fixed in dhcpcd version 7.0.7, which is the current package version.

See also