Provided by: udev_253.5-1ubuntu6.1_amd64 bug

NAME

       systemd.link - Network device configuration

SYNOPSIS

       link.link

DESCRIPTION

       A plain ini-style text file that encodes configuration for matching network devices, used
       by systemd-udevd(8) and in particular its net_setup_link builtin. See systemd.syntax(7)
       for a general description of the syntax.

       The .link files are read from the files located in the system network directory
       /lib/systemd/network and /usr/local/lib/systemd/network, the volatile runtime network
       directory /run/systemd/network, and the local administration network directory
       /etc/systemd/network. All configuration files are collectively sorted and processed in
       alphanumeric order, regardless of the directories in which they live. However, files with
       identical filenames replace each other. It is recommended that each filename is prefixed
       with a number (e.g.  10-eth0.link). Otherwise, the default .link files or those generated
       by systemd-network-generator.service(8) may take precedence over user configured files.
       Files in /etc/ have the highest priority, files in /run/ take precedence over files with
       the same name in /lib/. This can be used to override a system-supplied link file with a
       local file if needed. As a special case, an empty file (file size 0) or symlink with the
       same name pointing to /dev/null disables the configuration file entirely (it is "masked").

       Along with the link file foo.link, a "drop-in" directory foo.link.d/ may exist. All files
       with the suffix ".conf" from this directory will be merged in the alphanumeric order and
       parsed after the main file itself has been parsed. This is useful to alter or add
       configuration settings, without having to modify the main configuration file. Each drop-in
       file must have appropriate section headers.

       In addition to /etc/systemd/network, drop-in ".d" directories can be placed in
       /lib/systemd/network or /run/systemd/network directories. Drop-in files in /etc/ take
       precedence over those in /run/ which in turn take precedence over those in /lib/. Drop-in
       files under any of these directories take precedence over the main link file wherever
       located.

       The link file contains a [Match] section, which determines if a given link file may be
       applied to a given device, as well as a [Link] section specifying how the device should be
       configured. The first (in lexical order) of the link files that matches a given device is
       applied. Note that a default file 99-default.link is shipped by the system. Any
       user-supplied .link should hence have a lexically earlier name to be considered at all.

       See udevadm(8) for diagnosing problems with .link files.

[MATCH] SECTION OPTIONS

       A link file is said to match an interface if all matches specified by the [Match] section
       are satisfied. When a link file does not contain valid settings in [Match] section, then
       the file will match all interfaces and systemd-udevd warns about that. Hint: to avoid the
       warning and to make it clear that all interfaces shall be matched, add the following:

           OriginalName=*

       The first (in alphanumeric order) of the link files that matches a given interface is
       applied, all later files are ignored, even if they match as well. The following keys are
       accepted:

       MACAddress=
           A whitespace-separated list of hardware addresses. The acceptable formats are:

           colon-delimited hexadecimal
               Each field must be one byte. E.g.  "12:34:56:78:90:ab" or "AA:BB:CC:DD:EE:FF".

           hyphen-delimited hexadecimal
               Each field must be one byte. E.g.  "12-34-56-78-90-ab" or "AA-BB-CC-DD-EE-FF".

           dot-delimited hexadecimal
               Each field must be two bytes. E.g.  "1234.5678.90ab" or "AABB.CCDD.EEFF".

           IPv4 address format
               E.g.  "127.0.0.1" or "192.168.0.1".

           IPv6 address format
               E.g.  "2001:0db8:85a3::8a2e:0370:7334" or "::1".

           The total length of each MAC address must be 4 (for IPv4 tunnel), 6 (for Ethernet), 16
           (for IPv6 tunnel), or 20 (for InfiniBand). This option may appear more than once, in
           which case the lists are merged. If the empty string is assigned to this option, the
           list of hardware addresses defined prior to this is reset. Defaults to unset.

       PermanentMACAddress=
           A whitespace-separated list of hardware's permanent addresses. While MACAddress=
           matches the device's current MAC address, this matches the device's permanent MAC
           address, which may be different from the current one. Use full colon-, hyphen- or
           dot-delimited hexadecimal, or IPv4 or IPv6 address format. This option may appear more
           than once, in which case the lists are merged. If the empty string is assigned to this
           option, the list of hardware addresses defined prior to this is reset. Defaults to
           unset.

       Path=
           A whitespace-separated list of shell-style globs matching the persistent path, as
           exposed by the udev property ID_PATH.

       Driver=
           A whitespace-separated list of shell-style globs matching the driver currently bound
           to the device, as exposed by the udev property ID_NET_DRIVER of its parent device, or
           if that is not set, the driver as exposed by ethtool -i of the device itself. If the
           list is prefixed with a "!", the test is inverted.

       Type=
           A whitespace-separated list of shell-style globs matching the device type, as exposed
           by networkctl list. If the list is prefixed with a "!", the test is inverted. Some
           valid values are "ether", "loopback", "wlan", "wwan". Valid types are named either
           from the udev "DEVTYPE" attribute, or "ARPHRD_" macros in linux/if_arp.h, so this is
           not comprehensive.

       Kind=
           A whitespace-separated list of shell-style globs matching the device kind, as exposed
           by networkctl status INTERFACE or ip -d link show INTERFACE. If the list is prefixed
           with a "!", the test is inverted. Some valid values are "bond", "bridge", "gre",
           "tun", "veth". Valid kinds are given by netlink's "IFLA_INFO_KIND" attribute, so this
           is not comprehensive.

       Property=
           A whitespace-separated list of udev property names with their values after equals sign
           ("="). If multiple properties are specified, the test results are ANDed. If the list
           is prefixed with a "!", the test is inverted. If a value contains white spaces, then
           please quote whole key and value pair. If a value contains quotation, then please
           escape the quotation with "\".

           Example: if a .link file has the following:

               Property=ID_MODEL_ID=9999 "ID_VENDOR_FROM_DATABASE=vendor name" "KEY=with \"quotation\""

           then, the .link file matches only when an interface has all the above three
           properties.

       OriginalName=
           A whitespace-separated list of shell-style globs matching the device name, as exposed
           by the udev property "INTERFACE". This cannot be used to match on names that have
           already been changed from userspace. Caution is advised when matching on
           kernel-assigned names, as they are known to be unstable between reboots.

       Host=
           Matches against the hostname or machine ID of the host. See ConditionHost= in
           systemd.unit(5) for details. When prefixed with an exclamation mark ("!"), the result
           is negated. If an empty string is assigned, the previously assigned value is cleared.

       Virtualization=
           Checks whether the system is executed in a virtualized environment and optionally test
           whether it is a specific implementation. See ConditionVirtualization= in
           systemd.unit(5) for details. When prefixed with an exclamation mark ("!"), the result
           is negated. If an empty string is assigned, the previously assigned value is cleared.

       KernelCommandLine=
           Checks whether a specific kernel command line option is set. See
           ConditionKernelCommandLine= in systemd.unit(5) for details. When prefixed with an
           exclamation mark ("!"), the result is negated. If an empty string is assigned, the
           previously assigned value is cleared.

       KernelVersion=
           Checks whether the kernel version (as reported by uname -r) matches a certain
           expression. See ConditionKernelVersion= in systemd.unit(5) for details. When prefixed
           with an exclamation mark ("!"), the result is negated. If an empty string is assigned,
           the previously assigned value is cleared.

       Credential=
           Checks whether the specified credential was passed to the systemd-udevd.service
           service. See System and Service Credentials[1] for details. When prefixed with an
           exclamation mark ("!"), the result is negated. If an empty string is assigned, the
           previously assigned value is cleared.

       Architecture=
           Checks whether the system is running on a specific architecture. See
           ConditionArchitecture= in systemd.unit(5) for details. When prefixed with an
           exclamation mark ("!"), the result is negated. If an empty string is assigned, the
           previously assigned value is cleared.

       Firmware=
           Checks whether the system is running on a machine with the specified firmware. See
           ConditionFirmware= in systemd.unit(5) for details. When prefixed with an exclamation
           mark ("!"), the result is negated. If an empty string is assigned, the previously
           assigned value is cleared.

[LINK] SECTION OPTIONS

       The [Link] section accepts the following keys:

       Description=
           A description of the device.

       Alias=
           The ifalias interface property is set to this value.

       MACAddressPolicy=
           The policy by which the MAC address should be set. The available policies are:

           persistent
               If the hardware has a persistent MAC address, as most hardware should, and if it
               is used by the kernel, nothing is done. Otherwise, a new MAC address is generated
               which is guaranteed to be the same on every boot for the given machine and the
               given device, but which is otherwise random. This feature depends on ID_NET_NAME_*
               properties to exist for the link. On hardware where these properties are not set,
               the generation of a persistent MAC address will fail.

           random
               If the kernel is using a random MAC address, nothing is done. Otherwise, a new
               address is randomly generated each time the device appears, typically at boot.
               Either way, the random address will have the "unicast" and "locally administered"
               bits set.

           none
               Keeps the MAC address assigned by the kernel. Or use the MAC address specified in
               MACAddress=.

           An empty string assignment is equivalent to setting "none".

       MACAddress=
           The interface MAC address to use. For this setting to take effect, MACAddressPolicy=
           must either be unset, empty, or "none".

       NamePolicy=
           An ordered, space-separated list of policies by which the interface name should be
           set.  NamePolicy= may be disabled by specifying net.ifnames=0 on the kernel command
           line. Each of the policies may fail, and the first successful one is used. The name is
           not set directly, but is exported to udev as the property ID_NET_NAME, which is, by
           default, used by a udev(7), rule to set NAME. The available policies are:

           kernel
               If the kernel claims that the name it has set for a device is predictable, then no
               renaming is performed.

           database
               The name is set based on entries in the udev's Hardware Database with the key
               ID_NET_NAME_FROM_DATABASE.

           onboard
               The name is set based on information given by the firmware for on-board devices,
               as exported by the udev property ID_NET_NAME_ONBOARD. See systemd.net-naming-
               scheme(7).

           slot
               The name is set based on information given by the firmware for hot-plug devices,
               as exported by the udev property ID_NET_NAME_SLOT. See systemd.net-naming-
               scheme(7).

           path
               The name is set based on the device's physical location, as exported by the udev
               property ID_NET_NAME_PATH. See systemd.net-naming-scheme(7).

           mac
               The name is set based on the device's persistent MAC address, as exported by the
               udev property ID_NET_NAME_MAC. See systemd.net-naming-scheme(7).

           keep
               If the device already had a name given by userspace (as part of creation of the
               device or a rename), keep it.

       Name=
           The interface name to use. This option has lower precedence than NamePolicy=, so for
           this setting to take effect, NamePolicy= must either be unset, empty, disabled, or all
           policies configured there must fail. Also see the example below with "Name=dmz0".

           Note that specifying a name that the kernel might use for another interface (for
           example "eth0") is dangerous because the name assignment done by udev will race with
           the assignment done by the kernel, and only one interface may use the name. Depending
           on the order of operations, either udev or the kernel will win, making the naming
           unpredictable. It is best to use some different prefix, for example
           "internal0"/"external0" or "lan0"/"lan1"/"lan3".

           Interface names must have a minimum length of 1 character and a maximum length of 15
           characters, and may contain any 7bit ASCII character, with the exception of control
           characters, ":", "/" and "%". While "."  is an allowed character, it's recommended to
           avoid it when naming interfaces as various tools (such as resolvconf(1)) use it as
           separator character. Also, fully numeric interface names are not allowed (in order to
           avoid ambiguity with interface specification by numeric indexes), as are the special
           strings ".", "..", "all" and "default".

       AlternativeNamesPolicy=
           A space-separated list of policies by which the interface's alternative names should
           be set. Each of the policies may fail, and all successful policies are used. The
           available policies are "database", "onboard", "slot", "path", and "mac". If the kernel
           does not support the alternative names, then this setting will be ignored.

       AlternativeName=
           The alternative interface name to use. This option can be specified multiple times. If
           the empty string is assigned to this option, the list is reset, and all prior
           assignments have no effect. If the kernel does not support the alternative names, then
           this setting will be ignored.

           Alternative interface names may be used to identify interfaces in various tools. In
           contrast to the primary name (as configured with Name= above) there may be multiple
           alternative names referring to the same interface. Alternative names may have a
           maximum length of 127 characters, in contrast to the 15 allowed for the primary
           interface name, but otherwise are subject to the same naming constraints.

       TransmitQueues=
           Specifies the device's number of transmit queues. An integer in the range 1...4096.
           When unset, the kernel's default will be used.

       ReceiveQueues=
           Specifies the device's number of receive queues. An integer in the range 1...4096.
           When unset, the kernel's default will be used.

       TransmitQueueLength=
           Specifies the transmit queue length of the device in number of packets. An unsigned
           integer in the range 0...4294967294. When unset, the kernel's default will be used.

       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.

       BitsPerSecond=
           The speed to set for the device, the value is rounded down to the nearest Mbps. The
           usual suffixes K, M, G are supported and are understood to the base of 1000.

       Duplex=
           The duplex mode to set for the device. The accepted values are half and full.

       AutoNegotiation=
           Takes a boolean. If set to yes, automatic negotiation of transmission parameters is
           enabled. Autonegotiation is a procedure by which two connected ethernet devices choose
           common transmission parameters, such as speed, duplex mode, and flow control. When
           unset, the kernel's default will be used.

           Note that if autonegotiation is enabled, speed and duplex settings are read-only. If
           autonegotiation is disabled, speed and duplex settings are writable if the driver
           supports multiple link modes.

       WakeOnLan=
           The Wake-on-LAN policy to set for the device. Takes the special value "off" which
           disables Wake-on-LAN, or space separated list of the following words:

           phy
               Wake on PHY activity.

           unicast
               Wake on unicast messages.

           multicast
               Wake on multicast messages.

           broadcast
               Wake on broadcast messages.

           arp
               Wake on ARP.

           magic
               Wake on receipt of a magic packet.

           secureon
               Enable SecureOn password for MagicPacket. Implied when WakeOnLanPassword= is
               specified. If specified without WakeOnLanPassword= option, then the password is
               read from the credential "LINK.link.wol.password" (e.g.,
               "60-foo.link.wol.password"), and if the credential not found, then read from
               "wol.password". See LoadCredential=/SetCredential= in systemd.exec(1) for details.
               The password in the credential, must be 6 bytes in hex format with each byte
               separated by a colon (":") like an Ethernet MAC address, e.g.,
               "aa:bb:cc:dd:ee:ff".

           Defaults to unset, and the device's default will be used. This setting can be
           specified multiple times. If an empty string is assigned, then the all previous
           assignments are cleared.

       WakeOnLanPassword=
           Specifies the SecureOn password for MagicPacket. Takes an absolute path to a regular
           file or an AF_UNIX stream socket, or the plain password. When a path to a regular file
           is specified, the password is read from it. When an AF_UNIX stream socket is
           specified, a connection is made to it and the password is read from it. The password
           must be 6 bytes in hex format with each byte separated by a colon (":") like an
           Ethernet MAC address, e.g., "aa:bb:cc:dd:ee:ff". This implies WakeOnLan=secureon.
           Defaults to unset, and the current value will not be changed.

       Port=
           The port option is used to select the device port. The supported values are:

           tp
               An Ethernet interface using Twisted-Pair cable as the medium.

           aui
               Attachment Unit Interface (AUI). Normally used with hubs.

           bnc
               An Ethernet interface using BNC connectors and co-axial cable.

           mii
               An Ethernet interface using a Media Independent Interface (MII).

           fibre
               An Ethernet interface using Optical Fibre as the medium.

       Advertise=
           This sets what speeds and duplex modes of operation are advertised for
           auto-negotiation. This implies "AutoNegotiation=yes". The supported values are:

           Table 1. Supported advertise values
           ┌───────────────────┬──────────────┬─────────────┐
           │AdvertiseSpeed (Mbps)Duplex Mode │
           ├───────────────────┼──────────────┼─────────────┤
           │10baset-half       │ 10           │ half        │
           ├───────────────────┼──────────────┼─────────────┤
           │10baset-full       │ 10           │ full        │
           ├───────────────────┼──────────────┼─────────────┤
           │100baset-half      │ 100          │ half        │
           ├───────────────────┼──────────────┼─────────────┤
           │100baset-full      │ 100          │ full        │
           ├───────────────────┼──────────────┼─────────────┤
           │1000baset-half     │ 1000         │ half        │
           ├───────────────────┼──────────────┼─────────────┤
           │1000baset-full     │ 1000         │ full        │
           ├───────────────────┼──────────────┼─────────────┤
           │10000baset-full    │ 10000        │ full        │
           ├───────────────────┼──────────────┼─────────────┤
           │2500basex-full     │ 2500         │ full        │
           ├───────────────────┼──────────────┼─────────────┤
           │1000basekx-full    │ 1000         │ full        │
           ├───────────────────┼──────────────┼─────────────┤
           │10000basekx4-full  │ 10000        │ full        │
           ├───────────────────┼──────────────┼─────────────┤
           │10000basekr-full   │ 10000        │ full        │
           ├───────────────────┼──────────────┼─────────────┤
           │10000baser-fec     │ 10000        │ full        │
           ├───────────────────┼──────────────┼─────────────┤
           │20000basemld2-full │ 20000        │ full        │
           ├───────────────────┼──────────────┼─────────────┤
           │20000basekr2-full  │ 20000        │ full        │
           └───────────────────┴──────────────┴─────────────┘
           By default this is unset, i.e. all possible modes will be advertised. This option may
           be specified more than once, in which case all specified speeds and modes are
           advertised. If the empty string is assigned to this option, the list is reset, and all
           prior assignments have no effect.

       ReceiveChecksumOffload=
           Takes a boolean. If set to true, hardware offload for checksumming of ingress network
           packets is enabled. When unset, the kernel's default will be used.

       TransmitChecksumOffload=
           Takes a boolean. If set to true, hardware offload for checksumming of egress network
           packets is enabled. When unset, the kernel's default will be used.

       TCPSegmentationOffload=
           Takes a boolean. If set to true, TCP Segmentation Offload (TSO) is enabled. When
           unset, the kernel's default will be used.

       TCP6SegmentationOffload=
           Takes a boolean. If set to true, TCP6 Segmentation Offload (tx-tcp6-segmentation) is
           enabled. When unset, the kernel's default will be used.

       GenericSegmentationOffload=
           Takes a boolean. If set to true, Generic Segmentation Offload (GSO) is enabled. When
           unset, the kernel's default will be used.

       GenericReceiveOffload=
           Takes a boolean. If set to true, Generic Receive Offload (GRO) is enabled. When unset,
           the kernel's default will be used.

       GenericReceiveOffloadHardware=
           Takes a boolean. If set to true, hardware accelerated Generic Receive Offload (GRO) is
           enabled. When unset, the kernel's default will be used.

       LargeReceiveOffload=
           Takes a boolean. If set to true, Large Receive Offload (LRO) is enabled. When unset,
           the kernel's default will be used.

       ReceiveVLANCTAGHardwareAcceleration=
           Takes a boolean. If set to true, receive VLAN CTAG hardware acceleration is enabled.
           When unset, the kernel's default will be used.

       TransmitVLANCTAGHardwareAcceleration=
           Takes a boolean. If set to true, transmit VLAN CTAG hardware acceleration is enabled.
           When unset, the kernel's default will be used.

       ReceiveVLANCTAGFilter=
           Takes a boolean. If set to true, receive filtering on VLAN CTAGs is enabled. When
           unset, the kernel's default will be used.

       TransmitVLANSTAGHardwareAcceleration=
           Takes a boolean. If set to true, transmit VLAN STAG hardware acceleration is enabled.
           When unset, the kernel's default will be used.

       NTupleFilter=
           Takes a boolean. If set to true, receive N-tuple filters and actions are enabled. When
           unset, the kernel's default will be used.

       RxChannels=, TxChannels=, OtherChannels=, CombinedChannels=
           Specifies the number of receive, transmit, other, or combined channels, respectively.
           Takes an unsigned integer in the range 1...4294967295 or "max". If set to "max", the
           advertised maximum value of the hardware will be used. When unset, the number will not
           be changed. Defaults to unset.

       RxBufferSize=, RxMiniBufferSize=, RxJumboBufferSize=, TxBufferSize=
           Specifies the maximum number of pending packets in the NIC receive buffer, mini
           receive buffer, jumbo receive buffer, or transmit buffer, respectively. Takes an
           unsigned integer in the range 1...4294967295 or "max". If set to "max", the advertised
           maximum value of the hardware will be used. When unset, the number will not be
           changed. Defaults to unset.

       RxFlowControl=
           Takes a boolean. When set, enables receive flow control, also known as the ethernet
           receive PAUSE message (generate and send ethernet PAUSE frames). When unset, the
           kernel's default will be used.

       TxFlowControl=
           Takes a boolean. When set, enables transmit flow control, also known as the ethernet
           transmit PAUSE message (respond to received ethernet PAUSE frames). When unset, the
           kernel's default will be used.

       AutoNegotiationFlowControl=
           Takes a boolean. When set, auto negotiation enables the interface to exchange state
           advertisements with the connected peer so that the two devices can agree on the
           ethernet PAUSE configuration. When unset, the kernel's default will be used.

       GenericSegmentOffloadMaxBytes=
           Specifies the maximum size of a Generic Segment Offload (GSO) packet the device should
           accept. The usual suffixes K, M, G are supported and are understood to the base of
           1024. An unsigned integer in the range 1...65536. Defaults to unset.

       GenericSegmentOffloadMaxSegments=
           Specifies the maximum number of Generic Segment Offload (GSO) segments the device
           should accept. An unsigned integer in the range 1...65535. Defaults to unset.

       UseAdaptiveRxCoalesce=, UseAdaptiveTxCoalesce=
           Boolean properties that, when set, enable/disable adaptive Rx/Tx coalescing if the
           hardware supports it. When unset, the kernel's default will be used.

       RxCoalesceSec=, RxCoalesceIrqSec=, RxCoalesceLowSec=, RxCoalesceHighSec=, TxCoalesceSec=,
       TxCoalesceIrqSec=, TxCoalesceLowSec=, TxCoalesceHighSec=
           These properties configure the delay before Rx/Tx interrupts are generated after a
           packet is sent/received. The "Irq" properties come into effect when the host is
           servicing an IRQ. The "Low" and "High" properties come into effect when the packet
           rate drops below the low packet rate threshold or exceeds the high packet rate
           threshold respectively if adaptive Rx/Tx coalescing is enabled. When unset, the
           kernel's defaults will be used.

       RxMaxCoalescedFrames=, RxMaxCoalescedIrqFrames=, RxMaxCoalescedLowFrames=,
       RxMaxCoalescedHighFrames=, TxMaxCoalescedFrames=, TxMaxCoalescedIrqFrames=,
       TxMaxCoalescedLowFrames=, TxMaxCoalescedHighFrames=
           These properties configure the maximum number of frames that are sent/received before
           a Rx/Tx interrupt is generated. The "Irq" properties come into effect when the host is
           servicing an IRQ. The "Low" and "High" properties come into effect when the packet
           rate drops below the low packet rate threshold or exceeds the high packet rate
           threshold respectively if adaptive Rx/Tx coalescing is enabled. When unset, the
           kernel's defaults will be used.

       CoalescePacketRateLow=, CoalescePacketRateHigh=
           These properties configure the low and high packet rate (expressed in packets per
           second) threshold respectively and are used to determine when the corresponding
           coalescing settings for low and high packet rates come into effect if adaptive Rx/Tx
           coalescing is enabled. If unset, the kernel's defaults will be used.

       CoalescePacketRateSampleIntervalSec=
           Configures how often to sample the packet rate used for adaptive Rx/Tx coalescing.
           This property cannot be zero. This lowest time granularity supported by this property
           is seconds. Partial seconds will be rounded up before being passed to the kernel. If
           unset, the kernel's default will be used.

       StatisticsBlockCoalesceSec=
           How long to delay driver in-memory statistics block updates. If the driver does not
           have an in-memory statistic block, this property is ignored. This property cannot be
           zero. If unset, the kernel's default will be used.

       MDI=
           Specifies the medium dependent interface (MDI) mode for the interface. A MDI describes
           the interface from a physical layer implementation to the physical medium used to
           carry the transmission. Takes one of the following words: "straight" (or equivalently:
           "mdi"), "crossover" (or equivalently: "mdi-x", "mdix"), and "auto". When "straight",
           the MDI straight through mode will be used. When "crossover", the MDI crossover
           (MDI-X) mode will be used. When "auto", the MDI status is automatically detected.
           Defaults to unset, and the kernel's default will be used.

       SR-IOVVirtualFunctions=
           Specifies the number of SR-IOV virtual functions. Takes an integer in the range
           0...2147483647. Defaults to unset, and automatically determined from the values
           specified in the VirtualFunction= settings in the [SR-IOV] sections.

[SR-IOV] SECTION OPTIONS

       The [SR-IOV] section accepts the following keys. Specify several [SR-IOV] sections to
       configure several SR-IOVs. SR-IOV provides the ability to partition a single physical PCI
       resource into virtual PCI functions which can then be injected into a VM. In the case of
       network VFs, SR-IOV improves north-south network performance (that is, traffic with
       endpoints outside the host machine) by allowing traffic to bypass the host machine’s
       network stack.

       VirtualFunction=
           Specifies a Virtual Function (VF), lightweight PCIe function designed solely to move
           data in and out. Takes an integer in the range 0...2147483646. This option is
           compulsory.

       VLANId=
           Specifies VLAN ID of the virtual function. Takes an integer in the range 1...4095.

       QualityOfService=
           Specifies quality of service of the virtual function. Takes an integer in the range
           1...4294967294.

       VLANProtocol=
           Specifies VLAN protocol of the virtual function. Takes "802.1Q" or "802.1ad".

       MACSpoofCheck=
           Takes a boolean. Controls the MAC spoof checking. When unset, the kernel's default
           will be used.

       QueryReceiveSideScaling=
           Takes a boolean. Toggle the ability of querying the receive side scaling (RSS)
           configuration of the virtual function (VF). The VF RSS information like RSS hash key
           may be considered sensitive on some devices where this information is shared between
           VF and the physical function (PF). When unset, the kernel's default will be used.

       Trust=
           Takes a boolean. Allows one to set trust mode of the virtual function (VF). When set,
           VF users can set a specific feature which may impact security and/or performance. When
           unset, the kernel's default will be used.

       LinkState=
           Allows one to set the link state of the virtual function (VF). Takes a boolean or a
           special value "auto". Setting to "auto" means a reflection of the physical function
           (PF) link state, "yes" lets the VF to communicate with other VFs on this host even if
           the PF link state is down, "no" causes the hardware to drop any packets sent by the
           VF. When unset, the kernel's default will be used.

       MACAddress=
           Specifies the MAC address for the virtual function.

EXAMPLES

       Example 1. /lib/systemd/network/99-default.link

       The link file 99-default.link that is shipped with systemd defines the default naming
       policy for links.

           [Link]
           NamePolicy=kernel database on-board slot path
           MACAddressPolicy=persistent

       Example 2. /etc/systemd/network/10-dmz.link

       This example assigns the fixed name "dmz0" to the interface with the MAC address
       00:a0:de:63:7a:e6:

           [Match]
           MACAddress=00:a0:de:63:7a:e6

           [Link]
           Name=dmz0

       NamePolicy= is not set, so Name= takes effect. We use the "10-" prefix to order this file
       early in the list. Note that it needs to be before "99-link", i.e. it needs a numerical
       prefix, to have any effect at all.

       Example 3. Debugging NamePolicy= assignments

           $ sudo SYSTEMD_LOG_LEVEL=debug udevadm test-builtin net_setup_link /sys/class/net/hub0
           ...
           Parsed configuration file /lib/systemd/network/99-default.link
           Parsed configuration file /etc/systemd/network/10-eth0.link
           ID_NET_DRIVER=cdc_ether
           Config file /etc/systemd/network/10-eth0.link applies to device hub0
           link_config: autonegotiation is unset or enabled, the speed and duplex are not writable.
           hub0: Device has name_assign_type=4
           Using default interface naming scheme 'v240'.
           hub0: Policies didn't yield a name, using specified Name=hub0.
           ID_NET_LINK_FILE=/etc/systemd/network/10-eth0.link
           ID_NET_NAME=hub0
           ...

       Explicit Name= configuration wins in this case.

           sudo SYSTEMD_LOG_LEVEL=debug udevadm test-builtin net_setup_link /sys/class/net/enp0s31f6
           ...
           Parsed configuration file /lib/systemd/network/99-default.link
           Parsed configuration file /etc/systemd/network/10-eth0.link
           Created link configuration context.
           ID_NET_DRIVER=e1000e
           Config file /lib/systemd/network/99-default.link applies to device enp0s31f6
           link_config: autonegotiation is unset or enabled, the speed and duplex are not writable.
           enp0s31f6: Device has name_assign_type=4
           Using default interface naming scheme 'v240'.
           enp0s31f6: Policy *keep*: keeping existing userspace name
           enp0s31f6: Device has addr_assign_type=0
           enp0s31f6: MAC on the device already matches policy *persistent*
           ID_NET_LINK_FILE=/lib/systemd/network/99-default.link
           ...

       In this case, the interface was already renamed, so the keep policy specified as the first
       option in 99-default.link means that the existing name is preserved. If keep was removed,
       or if were in boot before the renaming has happened, we might get the following instead:

           enp0s31f6: Policy *path* yields "enp0s31f6".
           enp0s31f6: Device has addr_assign_type=0
           enp0s31f6: MAC on the device already matches policy *persistent*
           ID_NET_LINK_FILE=/lib/systemd/network/99-default.link
           ID_NET_NAME=enp0s31f6
           ...

       Please note that the details of output are subject to change.

       Example 4. /etc/systemd/network/10-internet.link

       This example assigns the fixed name "internet0" to the interface with the device path
       "pci-0000:00:1a.0-*":

           [Match]
           Path=pci-0000:00:1a.0-*

           [Link]
           Name=internet0

       Example 5. /etc/systemd/network/25-wireless.link

       Here's an overly complex example that shows the use of a large number of [Match] and
       [Link] settings.

           [Match]
           MACAddress=12:34:56:78:9a:bc
           Driver=brcmsmac
           Path=pci-0000:02:00.0-*
           Type=wlan
           Virtualization=no
           Host=my-laptop
           Architecture=x86-64

           [Link]
           Name=wireless0
           MTUBytes=1450
           BitsPerSecond=10M
           WakeOnLan=magic
           MACAddress=cb:a9:87:65:43:21

SEE ALSO

       systemd-udevd.service(8), udevadm(8), systemd.netdev(5), systemd.network(5), systemd-
       network-generator.service(8)

NOTES

        1. System and Service Credentials
           https://systemd.io/CREDENTIALS