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   systemd.network    ( 5 )

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[LINK] SECTION OPTIONS

The [Link] section accepts the following keys:

MACAddress= The hardware address to set for the device.

MTUBytes= The maximum transmission unit in bytes to set for the device. The usual suffixes K, M, G, are supported and are understood to the base of 1024.

Note that if IPv6 is enabled on the interface, and the MTU is chosen below 1280 (the minimum MTU for IPv6) it will automatically be increased to this value.

ARP= Takes a boolean. If set to true, the ARP (low-level Address Resolution Protocol) for this interface is enabled. When unset, the kernel's default will be used.

For example, disabling ARP is useful when creating multiple MACVLAN or VLAN virtual interfaces atop a single lower-level physical interface, which will then only serve as a link/"bridge" device aggregating traffic to the same physical link and not participate in the network otherwise. Defaults to unset.

Multicast= Takes a boolean. If set to true, the multicast flag on the device is enabled. Defaults to unset.

AllMulticast= Takes a boolean. If set to true, the driver retrieves all multicast packets from the network. This happens when multicast routing is enabled. Defaults to unset.

Promiscuous= Takes a boolean. If set to true, promiscuous mode of the interface is enabled. Defaults to unset.

If this is set to false for the underlying link of a "passthru" mode MACVLAN/MACVTAP, the virtual interface will be created with the "nopromisc" flag set.

Unmanaged= Takes a boolean. When "yes", no attempts are made to bring up or configure matching links, equivalent to when there are no matching network files. Defaults to "no".

This is useful for preventing later matching network files from interfering with certain interfaces that are fully controlled by other applications.

Group= Link groups are similar to port ranges found in managed switches. When network interfaces are added to a numbered group, operations on all the interfaces from that group can be performed at once. Takes an unsigned integer in the range 0...4294967295. Defaults to unset.

RequiredForOnline= Takes a boolean or a minimum operational state and an optional maximum operational state. Please see networkctl(1) for possible operational states. When "yes", the network is deemed required when determining whether the system is online (including when running systemd-networkd-wait-online). When "no", the network is ignored when determining the online state. When a minimum operational state and an optional maximum operational state are set, "yes" is implied, and this controls the minimum and maximum operational state required for the network interface to be considered online.

Defaults to "yes" when ActivationPolicy= is not set, or set to "up", "always-up", or "bound". Defaults to "no" when ActivationPolicy= is set to "manual" or "down". This is forced to "no" when ActivationPolicy= is set to "always-down".

The network will be brought up normally (as configured by ActivationPolicy=), but in the event that there is no address being assigned by DHCP or the cable is not plugged in, the link will simply remain offline and be skipped automatically by systemd-networkd-wait-online if "RequiredForOnline=no".

RequiredFamilyForOnline= Takes an address family. When specified, an IP address in the given family is deemed required when determining whether the link is online (including when running systemd-networkd-wait-online). Takes one of "ipv4", "ipv6", "both", or "any". Defaults to "any". Note that this option has no effect if "RequiredForOnline=no", or if "RequiredForOnline=" specifies a minimum operational state below "degraded".

ActivationPolicy= Specifies the policy for systemd-networkd managing the link administrative state. Specifically, this controls how systemd-networkd changes the network device's "IFF_UP" flag, which is sometimes controlled by system administrators by running e.g., ip set dev eth0 up or ip set dev eth0 down, and can also be changed with networkctl up eth0 or networkctl down eth0.

Takes one of "up", "always-up", "manual", "always-down", "down", or "bound". When "manual", systemd-networkd will not change the link's admin state automatically; the system administrator must bring the interface up or down manually, as desired. When "up" (the default) or "always-up", or "down" or "always-down", systemd-networkd will set the link up or down, respectively, when the interface is (re)configured. When "always-up" or "always-down", systemd-networkd will set the link up or down, respectively, any time systemd-networkd detects a change in the administrative state. When BindCarrier= is also set, this is automatically set to "bound" and any other value is ignored.

When the policy is set to "down" or "manual", the default value of RequiredForOnline= is "no". When the policy is set to "always-down", the value of RequiredForOnline= forced to "no".

The administrative state is not the same as the carrier state, so using "always-up" does not mean the link will never lose carrier. The link carrier depends on both the administrative state as well as the network device's physical connection. However, to avoid reconfiguration failures, when using "always-up", IgnoreCarrierLoss= is forced to true.