networkd.conf, networkd.conf.d — Global Network configuration files
These configuration files control global network parameters. Currently the DHCP Unique Identifier (DUID).
The default configuration is defined during compilation, so a
configuration file is only needed when it is necessary to deviate
from those defaults. By default, the configuration file in
/etc/systemd/ contains commented out entries
showing the defaults as a guide to the administrator. This file
can be edited to create local overrides.
When packages need to customize the configuration, they can
install configuration snippets in
/usr/lib/systemd/*.conf.d/. Files in
/etc/ are reserved for the local
administrator, who may use this logic to override the
configuration files installed by vendor packages. The main
configuration file is read before any of the configuration
directories, and has the lowest precedence; entries in a file in
any configuration directory override entries in the single
configuration file. Files in the
configuration subdirectories are sorted by their filename in lexicographic
order, regardless of which of the subdirectories they reside in. When
multiple files specify the same option, for options which accept just a
single value, the entry in the file with the lexicographically latest name
takes precedence. For options which accept a list of values, entries are
collected as they occur in files sorted lexicographically. It is recommended
to prefix all filenames in those subdirectories with a two-digit number and
a dash, to simplify the ordering of the files.
To disable a configuration file supplied by the vendor, the
recommended way is to place a symlink to
/dev/null in the configuration directory in
/etc/, with the same filename as the vendor
This section configures the DHCP Unique Identifier (DUID) value used by DHCP
protocol. DHCPv6 client protocol sends the DHCP Unique Identifier and the interface
Identity Association Identifier (IAID) to a DHCP server when acquiring a dynamic IPv6
address. DHCPv4 client protocol sends IAID and DUID to the DHCP server when acquiring
a dynamic IPv4 address if
ClientIdentifier=duid. IAID and DUID allows
a DHCP server to uniquely identify the machine and the interface requesting a DHCP IP.
To configure IAID and ClientIdentifier, see
The following options are understood:
Specifies how the DUID should be generated. See RFC 3315 for a description of all the options.
The following values are understood:
DUIDType=vendor", then the DUID value will be generated using
43793" as the vendor identifier (systemd) and hashed contents of
This is the default if
DUIDType= is not specified.
DUIDRawData= is not set,
then the product UUID is used as a DUID value. If a system does not have valid product UUID, then
is used as a DUID value. About the application-specific machine ID, see
link-layer-time" or "
link-layer" is specified,
then the MAC address of the interface is used as a DUID value. The value "
can take additional time value after a colon, e.g. "
link-layer-time:2018-01-23 12:34:56 UTC".
The default time value is "
2000-01-01 00:00:00 UTC".
In all cases,
DUIDRawData= can be used to override the
actual DUID value that is used.
Specifies the DHCP DUID value as a single newline-terminated, hexadecimal string, with each
byte separated by "
:". The DUID that is sent is composed of the DUID type specified by
DUIDType= and the value configured here.
The DUID value specified here overrides the DUID that systemd-networkd.service(8) generates from the machine ID. To configure DUID per-network, see systemd.network(5). The configured DHCP DUID should conform to the specification in RFC 3315, RFC 6355. To configure IAID, see systemd.network(5).
Example 1. A
DUIDType=vendor with a custom value
This specifies a 14 byte DUID, with the type DUID-EN ("
00:02"), enterprise number
00:00:ab:11"), and identifier value "