Difference between revisions of "Dhcpcd"

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#REDIRECT [[Network configuration#Dynamic IP address]]
{{Related articles start}}
{{Related|Network configuration}}
{{Related|Wireless network configuration}}
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[http://roy.marples.name/projects/dhcpcd/ dhcpcd] is a DHCP and DHCPv6 client. It is currently the most feature-rich open source DHCP client, see the home page for the full list of features.
{{Note|{{ic|dhcpcd}} (DHCP ''client'' daemon) is not the same as {{ic|dhcpd}} (DHCP ''(server)'' daemon).}}
== Installation ==
The {{Pkg|dhcpcd}} package is available in the [[official repositories]]. It is part of the {{Grp|base}} group, so it is likely already installed on your system.
You might be interested in {{AUR|dhcpcd-ui}}, which is a GTK+ frontend for the ''dhcpcd'' daemon (and optionally [[wpa_supplicant]]). It features a configuration dialogue and the ability to enter a pass phrase for wireless networks.
== Running ==
''dhcpcd'' is usually controlled via the provided service file {{ic|dhcpcd@.service}}, which takes the interface name as an argument (see [[systemd#Using units]] for details):
# systemctl start dhcpcd@''interface''.service
# systemctl enable dhcpcd@''interface''.service
To start ''dhcpcd'' manually, simply run the following command:
{{hc|# dhcpcd ''interface''|
dhcpcd: version 5.1.1 starting
dhcpcd: ''interface'': broadcasting for a lease
dhcpcd: ''interface'': leased for 86400 seconds
== Configuration ==
The main configuration is done in {{ic|/etc/dhcpcd.conf}}, see {{ic|dhcpcd.conf(5)}} for details. Some of the frequently used options are highlighted below.
=== 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:
# Use the same DUID + IAID as set in DHCPv6 for DHCPv4 Client ID as per RFC4361.
# Use the hardware address of the interface for the Client ID (DHCPv4).
Else, you may not obtain a lease since the DHCP server may not read your [http://en.wikipedia.org/wiki/DHCPv6 DHCPv6-style] Client ID correctly. See [http://tools.ietf.org/html/rfc4361 RFC 4361] for more information.
=== DHCP static route(s) ===
If you need to add a static route client-side, create a new dhcpcd hook-script in {{ic|/usr/lib/dhcpcd/dhcpcd-hooks}}. The example shows a new hook-script which adds a static route to a VPN subnet on {{ic|}} via a gateway machine at {{ic|}}:
ip route add via
The {{ic|40}} prefix means that it is the final hook-script to run when dhcpcd starts.
=== Speed up DHCP by disabling ARP probing ===
''dhcpcd'' contains an implementation of a recommendation of the DHCP standard ([http://www.ietf.org/rfc/rfc2131.txt 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 {{ic|/etc/dhcpcd.conf}}:
This is equivalent to passing {{ic|--noarp}} to {{ic|dhcpcd}}, and disables the described ARP probing, speeding up connections to networks with DHCP.
== Tips and tricks ==
=== Remove old DHCP lease ===
The file {{ic|/var/lib/dhcpcd/dhcpcd-''interface''.lease}}, where {{ic|''interface''}} is the name of the interface on which you have a lease, contains the actual DHCP lease reply sent by the DHCP server. It is used to determine the last lease from the server, and its {{ic|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.
== Troubleshooting ==
=== Check DHCP problem by releasing IP first ===
Problem may occur when DHCP get wrong IP assignment. For example when two routers are tied together through VPN. The router that is connected to me by VPN may assigning IP address. To fix it. On a console, as root, release IP address:
# dhcpcd -k
Then request a new one:
# dhcpcd
Maybe you had to run those two commands many times.
=== Problems with incompliant routers ===
For some (incompliant) routers, you will not be able to connect properly unless you comment the line
require dhcp_server_identifier
in {{ic|/etc/dhcpcd.conf}}. This should not cause issues unless you have multiple DHCP servers on your network (not typical); see [http://technet.microsoft.com/en-us/library/cc977442.aspx this page] for more information.
== Hooks ==
''dhcpcd'' executes all scripts found in {{ic|/usr/lib/dhcpcd/dhcpcd-hooks/}} in a lexical order. See {{ic|dhcpcd(5)}} and {{ic|dhcpcd-run-hooks(8)}} for details.
* Each script can be disabled using the {{ic|nohook}} option in {{ic|dhcpcd.conf}}.
* The {{ic|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 {{ic|1=env force_hostname=YES}}.
{{Expansion|describe (at least some) provided hooks, e.g. {{ic|10-wpa_supplicant}}}}

Revision as of 13:50, 18 February 2014