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 *.conf.d/ 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
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 configuration file.
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
. 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 systemd.network
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:
If "DUIDType=vendor", then the DUID
value will be generated using "43793" as the vendor identifier
(systemd) and hashed contents of machine-id(5). This is the default if
DUIDType= is not specified.
Those values are parsed and can be used to set
the DUID type field, but DUID contents must be provided using
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
and the value configured here.
The DUID value specified here overrides the DUID that systemd-networkd generates
using the machine-id from the /etc/machine-id file. To configure DUID
per-network, see systemd.network
(5). The configured DHCP DUID should
conform to the specification in RFC 3315
, RFC 6355
configure IAID, see systemd.network
Example 1. A DUIDType=vendor with a custom value
This specifies a 14 byte DUID, with the type DUID-EN ("00:02"),
enterprise number 43793 ("00:00:ab:11"), and identifier value
- RFC 3315
- RFC 3315
- RFC 6355