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DHCPCD.CONF

Section: File Formats (5)
Index Return to Main Contents

BSD mandoc
 

NAME

dhcpcd.conf - dhcpcd configuration file  

DESCRIPTION

Although dhcpcd can do everything from the command line, there are cases where it's just easier to do it once in a configuration file. Most of the options found in dhcpcd(8) can be used here. The first word on the line is the option and the rest of the line is the value. Leading and trailing whitespace for the option and value are trimmed. You can escape characters in the value using the \ character.

Blank lines and lines starting with # are ignored.

Here's a list of available options:

allowinterfaces pattern
When discovering interfaces, the interface name must match pattern which is a space or comma separated list of patterns passed to fnmatch(3). If the same interface is matched in denyinterfaces then it is still denied.
denyinterfaces pattern
When discovering interfaces, the interface name must not match pattern which is a space or comma separated list of patterns passed to fnmatch(3).
arping address [address]
dhcpcd will arping each address in order before attempting DHCP. If an address is found, we will select the replying hardware address as the profile, otherwise the ip address. Example:

authprotocol protocol algorithm rdm
Authenticate DHCP messages. See the Supported Authentication Protocols section.
authtoken secretid realm expire key
Define a shared key for use in authentication. realm can be to for use with the delayed prptocol. expire is the date the token expires and should be formatted "yyy-mm-dd HH:MM". You can use the keyword forever or 0 which means the token never expires. For the token protocol, secretid needs to be 0 and realm needs to be "". If dhcpcd has the error then it means that dhcpcd could not find the correct authentication token in your configuration.
background
Background immediately. This is useful for startup scripts which don't disable link messages for carrier status.
blacklist address [/cidr]
Ignores all packets from address [/cidr]
whitelist address [/cidr]
Only accept packets from address [/cidr] blacklist is ignored if whitelist is set.
broadcast
Instructs the DHCP server to broadcast replies back to the client. Normally this is only set for non Ethernet interfaces, such as FireWire and InfiniBand. In most cases, dhcpcd will set this automatically.
controlgroup group
Sets the group ownership of /run/dhcpcd.sock so that users other than root can connect to dhcpcd
debug
Echo debug messages to the stderr and syslog.
dev value
Load the value /dev management module. dhcpcd will load the first one found to work, if any.
env value
Push value to the environment for use in dhcpcd-run-hooks8. For example, you can force the hostname hook to always set the hostname with env force_hostname=YES Or set which driver wpa_supplicant8 should use with env wpa_supplicant_driver=nl80211

If the hostname is set, will be will set to the FQDN if possible as per RFC 4702 section 3.1. If the FQDN option is missing, dhcpcd will still try and set a FQDN from the hostname and domain options for consistency. To override this, set env hostname_fqdn=[YES|NO|SERVER] A value of server means just what the server says, don't manipulate it. This could lead to an inconsistent hostname on a DHCPv4 and DHCPv6 network where the DHCPv4 hostname is short and the DHCPv6 has an FQDN. DHCPv6 has no hostname option.

clientid string
Send the clientid If the string is of the format 01:02:03 then it is encoded as hex. For interfaces whose hardware address is longer than 8 bytes, or if the clientid is an empty string then dhcpcd sends a default clientid of the hardware family and the hardware address.
duid
Generate an
"RFC 4361"
compliant DHCP Unique Identifier. If persistent storage is available then a DUID-LLT (link local address + time) is generated, otherwise DUID-LL is generated (link local address). This, plus the IAID will be used as the clientid The DUID-LLT generated will be held in /etc/dhcpcd.duid and should not be copied to other hosts.
iaid iaid
Set the Interface Association Identifier to iaid This option must be used in an interface block. This defaults to the last 4 bytes of the hardware address assigned to the interface. Each instance of this should be unique within the scope of the client and dhcpcd warns if a conflict is detected. If there is a conflict, it is only a problem if the conflicted IAIDs are used on the same network.
dhcp
Enable DHCP on the interface, on by default.
dhcp6
Enable DHCPv6 on the interface, on by default.
ipv4
Enable IPv4 on the interface, on by default.
ipv6
Enable IPv6 on the interface, on by default.
persistent
dhcpcd normally de-configures the interface and configuration when it exits. Sometimes, this isn't desirable if, for example, you have root mounted over NFS or SSH clients connect to this host and they need to be notified of the host shutting down. You can use this option to stop this from happening.
fallback profile
Fallback to using this profile if DHCP fails. This allows you to configure a static profile instead of using ZeroConf.
hostname name
Sends hostname to the DHCP server so it can be registered in DNS. If hostname is an empty string then the current system hostname is sent. If hostname is a FQDN (ie, contains a .) then it will be encoded as such.
hostname_short
Sends the short hostname to the DHCP server instead of the FQDN. This is useful because DHCP servers will not register the FQDN in their DNS if the domain part does not match theirs.

Also, see the env option above to control how the hostname is set on the host.

ia_na [iaid [/ address] ]
Request a DHCPv6 Normal Address for iaid iaid defaults to the iaid option as described above. You can request more than one ia_na by specifying a unique iaid for each one.
ia_ta [iaid ]
Request a DHCPv6 Temporary Address for iaid You can request more than one ia_ta by specifying a unique iaid for each one.
ia_pd [iaid [/ prefix / prefix_len [interface [/ sla_id [/ prefix_len ] ] ] ] ]
Request a DHCPv6 Delegated Prefix for iaid This option must be used in an interface block. Unless a sla_id of 0 is assigned, a reject route is installed for the Delegated Prefix to stop unallocated addresses being resolved upstream. If no interface is given then we will assign a prefix to every other interface with a sla_id equivalent to the interface index assigned by the OS. Otherwise addresses are only assigned for each interface and sla_id Each assigned address will have a suffix of 1. You cannot assign a prefix to the requesting interface unless the DHCPv6 server supports RFC6603 Prefix Exclude Option. dhcpcd has to be running for all the interfaces it is delegating to. A default prefix_len of 64 is assumed, unless the maximum sla_id does not fit. In this case prefix_len is increased to the highest multiple of 8 that can accommodate the sla_id sla_id is an integer and is added to the prefix which must fit inside prefix_len less the length of the delegated prefix. sla_id can be 0 only if the Delegated Prefix is assigned to one interface. You can specify multiple interface sla_id prefix_len per ia_pd space separated. IPv6RS should be disabled globally when requesting a Prefix Delegation.

In the following example eth0 is the externally facing interface to be configured for both IPv4 and IPv6. The DHCPv4 server will provide us with an IPv4 address and a default route. The DHCPv6 server is going to provide us with an IPv6 address, a default route and a /64 subnet to be delegated to the internal interface. The eth1 interface will be automatically configured for IPv6 using the first address (::1) from the delegated prefix. rtadvd(8) can be used with an empty configuration file on eth1 to provide automatic IPv6 address configuration for the internal network.

noipv6rs            # disable routing solicitation
denyinterfaces eth2 # Don't touch eth2 at all
interface eth0
    ipv6rs          # enable routing solicitation get the
                    # default IPv6 route
    ia_na 1         # request an IPv6 address
    ia_pd 2 eth1/0  # get a /64 and assign it to eth1
ia_pd_mix
To be RFC compliant, dhcpcd cannot mix Prefix Delegation with other DHCPv6 address types in the same session. This has a number of issues: additional DHCP traffic and potential collisions between options. ia_pd_mix enables draft-ietf-dhc-dhcpv6-stateful-issues-06 support so that Prefix Delegation can be mixed with other address types in the same session.
ipv4only
Only configure IPv4.
ipv6only
Only confgiure IPv6.
fqdn [disable | ptr | both]
ptr just asks the DHCP server to update the PTR record of the host in DNS whereas both also updates the A record. disable will disable the FQDN option. The default is both. dhcpcd itself never does any DNS updates. dhcpcd encodes the FQDN hostname as specified in RFC1035
interface interface
Subsequent options are only parsed for this interface
ipv6ra_autoconf
Generate SLAAC addresses for each Prefix advertised by a Router Advertisement message with the Auto flag set. On by default.
ipv6ra_noautoconf
Disables the above option.
ipv6ra_fork
By default, when dhcpcd receives an IPv6 RA, dhcpcd will only fork to the background if the RA contains at least one unexpired RDNSS option and a valid prefix or no DHCPv6 instruction. Set this option so to make dhcpcd always fork on an RA.
ipv6ra_own
Disables kernel IPv6 Router Advertisment processing so dhcpcd can manage addresses and routes.
ipv6ra_own_default
Each time dhcpcd receives an IPv6 Router Adveristment, dhcpcd will manage the default route only. This allows dhcpcd to prefer an interface for outbound traffic based on metric and/or user selection rather than the kernel.
ipv6rs
Enables IPv6 Router Advertisment solicitation. This is on by default, but is documented here in the case where it is disabled globally but needs to be enabled for one interface.
leasetime seconds
Request a leasetime of seconds
metric metric
Metrics are used to prefer an interface over another one, lowest wins. dhcpcd will supply a default metric of 200 + if_nametoindex3. An extra 100 will be added for wireless interfaces.
noalias
Any pre-existing IPv4 addresses existing address will be removed from the interface when adding a new IPv4 address.
noarp
Don't send any ARP requests. This also disables IPv4LL.
noauthrequired
Don't require authentication even though we requested it.
nodev
Don't load /dev management modules.
nodhcp
Don't start DHCP or listen to DHCP messages. This is only useful when allowing IPv4LL.
nodhcp6
Don't start DHCPv6 or listen to DHCPv6 messages. Normally DHCPv6 is started by a RA instruction or configuration.
nogateway
Don't install any default routes.
gateway
Install a default route if available (default).
nohook script
Don't run this hook script. Matches full name, or prefixed with 2 numbers optionally ending with .sh

So to stop dhcpcd from touching your DNS or MTU settings you would do:-

noipv4
Don't attempt to configure an IPv4 address.
noipv4ll
Don't attempt to obtain an IPv4LL address if we failed to get one via DHCP. See
"RFC 3927"
noipv6
Don't attmept to configure an IPv6 address.
noipv6rs
Disable solicitation and receipt of IPv6 Router Advertisements.
nolink
Don't receive link messages about carrier status. You should only set this for buggy interface drivers.
option option
Requests the option from the server. It can be a variable to be used in dhcpcd-run-hooks8 or the numerical value. You can specify more option s separated by commas, spaces or more option lines. Prepend dhcp6_ to option to request a DHCPv6 option. DHCPv4 options are mapped to DHCPv6 where applicable.
nooption option
Remove the option from the DHCP message. This should only be used when a DHCP server sends a non requested option that should not be processed.
destination option
If detects an address added to a point to point interface (PPP, TUN, etc) then it will set the listed DHCP options to the destination address of the interface.
profile name
Subsequent options are only parsed for this profile name
quiet
Suppress any dhcpcd output to the console, except for errors.
reboot seconds
Allow reboot seconds before moving to the DISCOVER phase if we have an old lease to use and moving from DISCOVER to IPv4LL if no reply. The default is 5 seconds. A setting of 0 seconds causes dhcpcd to skip the REBOOT phase and go straight into DISCOVER. This is desirable for mobile users because if you change from network A to network B and they use the same subnet and the address from network A isn't in use on network B, then the DHCP server will remain silent even if authorative which means dhcpcd will timeout before moving back to the DISCOVER phase.
release
dhcpcd will release the lease prior to stopping the interface.
require option
Requires the option to be present in all DHCP messages, otherwise the message is ignored. It can be a variable to be used in dhcpcd-run-hooks8 or the numerical value. You can specify more options separated by commas, spaces or more require lines. To enforce that dhcpcd only responds to DHCP servers and not BOOTP servers, you can require dhcp_message_type This isn't an exact science though because a BOOTP server can send DHCP like options.
reject option
Reject a DHCP message that contains the option This is useful when you cannot use require to select / de-select BOOTP messages.
script script
Use script instead of the default /lib/dhcpcd/dhcpcd-run-hooks
ssid ssid
Subsequent options are only parsed for this wireless ssid
slaac [hwaddr | private ]
Selects the interface identifier used for SLAAC generated IPv6 addresses. If private is used, a RFC7217 address is generated.
static value
Configures a static value If you set ip_address then dhcpcd will not attempt to obtain a lease and just use the value for the address with an infinite lease time.

Here is an example which configures a static address, routes and dns.

Here is an example for PPP which gives the destination a default route. It uses the special destination keyword to insert the destination address into the value.

timeout seconds
Timeout after seconds instead of the default 30. A setting of 0 seconds causes dhcpcd to wait forever to get a lease. If dhcpcd is working on a single interface then dhcpcd will exit when a timeout occurs, otherwise dhcpcd will fork into the background. If using IPv4LL then dhcpcd start the IPv4LL process after the timeout and then wait a little longer before really timing out.
userclass string
Tag the DHCPv4 messages with the userclass. You can specify more than one.
vendor code , value
Add an encapsulated vendor option. code should be between 1 and 254 inclusive. To add a raw vendor string, omit code but keep the comma. Examples.

Set the vendor option 01 with an IP address. Set the vendor option 02 with a hex code. Set the vendor option 03 with an IP address as a string. Set un-encapsulated vendor option to hello world.

vendorclassid string
Set the DHCP Vendor Class. DHCPv6 has it's own option as shown below. The default is dhcpcd-<version>:<os>:<machine>:<platform>. For example If not set then none is sent. Some badly configured DHCP servers reject unknown vendorclassids. To work around it, try and impersonate Windows by using the MSFT vendorclassid.
vendclass en data
Add the DHCPv6 Vendor Indetifying Vendor Class with the IANA assigned Enterprise Number en with the data This option can be set more than once to add more data, but the behaviour, as per RFC(3925) is undefined if the Enterprise Number differs.
waitip [4 | 6]
Wait for an address to be assigned before forking to the background. 4 means wait for an IPv4 address to be assigned. 6 means wait for an IPv6 address to be assigned. If no argument is given, will wait for any address protocol to be assigned. It is possible to wait for more than one address protocol and will only fork to the background when all waiting conditions are satisfied.
xidhwaddr
Use the last four bytes of the hardware address as the DHCP xid instead of a randomly generated number.

 

Defining new options

DHCP allows for the use of custom options. Each option needs to be started with the define or define6 directive. This can optionally be followed by both embed or encap options. Both can be specified more than once and embed must come before encap

define code type variable
Defines the DHCP option code of type with a name of variable exported to dhcpcd-run-hooks8.
define6 code type variable
Defines the DHCPv6 option code of type with a name of variable exported to dhcpcd-run-hooks8, with a prefix of _dhcp6
vendopt code type variable
Defines the Vendor-Identifying Vendor Options. The code is the IANA Enterprise Number which will unqiuely describe the encapsulated options. type is normally encap variable names the Vendor option to be exported.
embed type variable
Defines an embedded variable within the defined option. The length is determined by the type If the variable is not the same as defined in the parent option, it is prefixed with the parent variable first with an underscore.
encap code type variable
Defines an encapsulated variable within the defined option. The length is determined by the type If the variable is not the same as defined in the parent option, it is prefixed with the parent variable first with an underscore.

 

Type prefix

These keywords come before the type itself, to describe it more fully. You can use more than one, but they must appear in the order listed below.

request
Requests the option by default without having to be specified in user configuration
norequest
This option cannot be requested, regardless of user configuration
index
The option can appear more than once and will be indexed.
array
The option data is split into a space separated array, each element being the same type.

 

Types to define

The type directly affects the length of data consumed inside the option. Any remaining data is normally discarded. Lengths can be specified for string and binhex types, but this is generally with other data embedded afterwards in the same option.

ipaddress
An IPv4 address, 4 bytes
ip6address
An IPv6 address, 16 bytes
string [: length ]
A NVT ASCII string of printable characters.
byte
A byte
int16
A signed 16bit integer, 2 bytes
uint16
An unsigned 16bit integer, 2 bytes
int32
A signed 32bit integer, 4 bytes
uint32
An unsigned 32bit integer, 4 bytes
flag
A fixed value (1) to indicate that the option is present, 0 bytes
domain
A RFC 3397 encoded string
dname
A RFC 1035 validated string
binhex [: length ]
Binary data expressed as hexadecimal
embed
Contains embedded options (implies encap as well)
encap
Contains encapsulated options (implies embed as well)
option
References an option from the global definition

 

Example definition

 

Supported Authentication Protocols

token
Sends and expects the token with the secretid 0 and realm of "" in each message.
delayedrealm
Delayed Authentication. dhcpcd will send an authentication option with no key or MAC. The server will see this option, and select a key for , writing the realm and secretid in it. dhcpcd will then look for a non-expired token with a matching realm and secretid. This token is used to authenicate all other messages.
delayed
Same as above, but without a realm.

 

Supported Authentication Algorithms

If none specified, hmac-md5 is the default.

hmac-md5

 

Supported Replay Detection Mechanisms

If none specified, monotonic is the default. If this is changed from what was previously used, or the means of calculating or storing it is broken then the DHCP server will probably have to have its notion of the clients Replay Detection Value reset.

monocounter
Read the number in the file /var/lib/dhcpcd/dhcpcd-rdm.monotonic and add one to it.
monotime
Create a NTP timestamp from the system time.
monotonic
Same as monotime

 

SEE ALSO

fnmatch(3), if_nametoindex3, dhcpcd(8), dhcpcd-run-hooks8  

AUTHORS

An Roy Marples Aq Mt roy@marples.name  

BUGS

Please report them to Lk http://roy.marples.name/projects/dhcpcd


 

Index

NAME
DESCRIPTION
Defining new options
Type prefix
Types to define
Example definition
Supported Authentication Protocols
Supported Authentication Algorithms
Supported Replay Detection Mechanisms
SEE ALSO
AUTHORS
BUGS


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