Network-networkd: Difference between revisions

Revision as of 13:00, 15 January 2023

Setup for Networkd

Switching to Networkd

$ systemctl stop NetworkManager 
$ systemctl disable NetworkManager 
$ systemctl enable systemd-networkd
$ systemctl enable systemd-resolved
$ systemctl start systemd-resolved
$ rm /etc/resolv.conf
$ ln -s /run/systemd/resolve/resolv.conf /etc/resolv.conf
$ mkdir -p /etc/systemd/network

Configuring Networkd

What interfaces do we have

# networkctl
IDX LINK            TYPE     OPERATIONAL SETUP    
  1 lo              loopback carrier     unmanaged
  2 eno1            ether    routable    unmanaged
  3 br0             bridge   routable    unmanaged
  4 virbr0          bridge   no-carrier  unmanaged
  5 docker0         bridge   no-carrier  unmanaged
  6 br-b737ea16f9fc bridge   no-carrier  unmanaged
  7 vnet0           ether    degraded    unmanaged

7 links listed.

Configuring en01 - static

$ cat >> /etc/systemd/network/00-eno1.network << EOF
[Match]
Name=enp3s0

[Network]
Address=192.168.1.50/24
Gateway=192.168.1.1
DNS=192.168.1.1
EOF

Configuring en01 - dhcp

$ cat >> /etc/systemd/network/00-eno1.network << EOF
[Match]
Name=enp3s0

[Network]
DHCP=yes
EOF

Controlling interfaces

Full Restart

$ systemctl restart systemd-network

Interface only

Link up and down (does not reconfigure)

$ networkctl up eno1

$ networkctl down eno1

Reconfigure interface based on configuration file

$ networkctl reconfigure eno1

networkd useful commands

$ networkctl list
IDX LINK            TYPE     OPERATIONAL SETUP    
  1 lo              loopback carrier     unmanaged
  2 eno1            ether    off         unmanaged
  3 virbr0          bridge   no-carrier  unmanaged
  4 br-b737ea16f9fc bridge   no-carrier  unmanaged
  5 docker0         bridge   no-carrier  unmanaged

5 links listed.
root@workstation2:/etc/systemd/network# !ping

IP Alias for Networkd

Adding an alias to an interface in networkd is closely related to the ip command, where the device simply receives more addresses on the interfaces. It does not show up as a an aliased device, which IMO makes it harder to understand, but YMMV.

$ cat >> /etc/systemd/network/00-eno1.network << EOF
[Match]
Name=enp3s0
[Network]
Address=192.168.1.50/24
Address=172.14.0.50/24
Gateway=192.168.1.1
DNS=192.168.1.1
EOF

Networkd Configuration Paramters (from ubuntu's man pages)

[Match] Section

MACAddress=
The hardware address of the interface (use full colon-delimited hexadecimal, e.g.,
01:23:45:67:89:ab).

Path=
A whitespace-separated list of shell-style globs matching the persistent path, as
exposed by the udev property "ID_PATH". If the list is prefixed with a "!", the test
is inverted; i.e. it is true when "ID_PATH" does not match any item in the list.

Driver=
A whitespace-separated list of shell-style globs matching the driver currently bound
to the device, as exposed by the udev property "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 the udev property "DEVTYPE". If the list is prefixed with a "!", the test is
inverted.

Name=
A whitespace-separated list of shell-style globs matching the device name, as exposed
by the udev property "INTERFACE". If the list is prefixed with a "!", the test is
inverted.

Host=
Matches against the hostname or machine ID of the host. See "ConditionHost=" in
systemd.unit(5) for details.

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.

KernelCommandLine=
Checks whether a specific kernel command line option is set (or if prefixed with the
exclamation mark unset). See "ConditionKernelCommandLine=" in systemd.unit(5) for
details.

KernelVersion=
Checks whether the kernel version (as reported by uname -r) matches a certain
expression (or if prefixed with the exclamation mark does not match it). See
"ConditionKernelVersion=" in systemd.unit(5) for details.

Architecture=
Checks whether the system is running on a specific architecture. See
"ConditionArchitecture=" in systemd.unit(5) for details.

[Link] Section

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=
A boolean. Enables or disables the ARP (low-level Address Resolution Protocol) for
this interface. Defaults to unset, which means that the kernel 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.

Unmanaged=
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.

RequiredForOnline=
A boolean. When "yes", the network is deemed required when determining whether the
system is online when running "systemd-networkd-wait-online". When "no", the network
is ignored when checking for online state. Defaults to "yes".

The network will be brought up normally in all cases, 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=true".

[Netork] Section

The "[Network]" section accepts the following keys:

Description=
A description of the device. This is only used for presentation purposes.

DHCP=
Enables DHCPv4 and/or DHCPv6 client support. Accepts "yes", "no", "ipv4", or "ipv6".
Defaults to "no".

Note that DHCPv6 will by default be triggered by Router Advertisement, if that is
enabled, regardless of this parameter. By enabling DHCPv6 support explicitly, the
DHCPv6 client will be started regardless of the presence of routers on the link, or
what flags the routers pass. See "IPv6AcceptRA=".

Furthermore, note that by default the domain name specified through DHCP, on Ubuntu,
are used for name resolution. See option UseDomains= below.

See the "[DHCP]" section below for further configuration options for the DHCP client
support.

DHCPServer=
A boolean. Enables DHCPv4 server support. Defaults to "no". Further settings for the
DHCP server may be set in the "[DHCPServer]" section described below.

LinkLocalAddressing=
Enables link-local address autoconfiguration. Accepts "yes", "no", "ipv4", or "ipv6".
Defaults to "ipv6".

IPv4LLRoute=
A boolean. When true, sets up the route needed for non-IPv4LL hosts to communicate
with IPv4LL-only hosts. Defaults to false.

IPv6Token=
An IPv6 address with the top 64 bits unset. When set, indicates the 64-bit interface
part of SLAAC IPv6 addresses for this link. Note that the token is only ever used for
SLAAC, and not for DHCPv6 addresses, even in the case DHCP is requested by router
advertisement. By default, the token is autogenerated.

LLMNR=
A boolean or "resolve". When true, enables Link-Local Multicast Name Resolution[1] on
the link. When set to "resolve", only resolution is enabled, but not host registration
and announcement. Defaults to true. This setting is read by systemd-
resolved.service(8).

MulticastDNS=
A boolean or "resolve". When true, enables Multicast DNS[2] support on the link. When
set to "resolve", only resolution is enabled, but not host or service registration and
announcement. Defaults to false. This setting is read by systemd-resolved.service(8).

DNSSEC=
A boolean or "allow-downgrade". When true, enables DNSSEC[3] DNS validation support on
the link. When set to "allow-downgrade", compatibility with non-DNSSEC capable
networks is increased, by automatically turning off DNSSEC in this case. This option
defines a per-interface setting for resolved.conf(5)'s global DNSSEC= option. Defaults
to false. This setting is read by systemd-resolved.service(8).

DNSSECNegativeTrustAnchors=
A space-separated list of DNSSEC negative trust anchor domains. If specified and
DNSSEC is enabled, look-ups done via the interface's DNS server will be subject to the
list of negative trust anchors, and not require authentication for the specified
domains, or anything below it. Use this to disable DNSSEC authentication for specific
private domains, that cannot be proven valid using the Internet DNS hierarchy.
Defaults to the empty list. This setting is read by systemd-resolved.service(8).

LLDP=
Controls support for Ethernet LLDP packet reception. LLDP is a link-layer protocol
commonly implemented on professional routers and bridges which announces which
physical port a system is connected to, as well as other related data. Accepts a
boolean or the special value "routers-only". When true, incoming LLDP packets are
accepted and a database of all LLDP neighbors maintained. If "routers-only" is set
only LLDP data of various types of routers is collected and LLDP data about other
types of devices ignored (such as stations, telephones and others). If false, LLDP
reception is disabled. Defaults to "routers-only". Use networkctl(1) to query the
collected neighbor data. LLDP is only available on Ethernet links. See EmitLLDP= below
for enabling LLDP packet emission from the local system.

EmitLLDP=
Controls support for Ethernet LLDP packet emission. Accepts a boolean parameter or the
special values "nearest-bridge", "non-tpmr-bridge" and "customer-bridge". Defaults to
false, which turns off LLDP packet emission. If not false, a short LLDP packet with
information about the local system is sent out in regular intervals on the link. The
LLDP packet will contain information about the local host name, the local machine ID
(as stored in machine-id(5)) and the local interface name, as well as the pretty
hostname of the system (as set in machine-info(5)). LLDP emission is only available on
Ethernet links. Note that this setting passes data suitable for identification of host
to the network and should thus not be enabled on untrusted networks, where such
identification data should not be made available. Use this option to permit other
systems to identify on which interfaces they are connected to this system. The three
special values control propagation of the LLDP packets. The "nearest-bridge" setting
permits propagation only to the nearest connected bridge, "non-tpmr-bridge" permits
propagation across Two-Port MAC Relays, but not any other bridges, and
"customer-bridge" permits propagation until a customer bridge is reached. For details
about these concepts, see IEEE 802.1AB-2009[4]. Note that configuring this setting to
true is equivalent to "nearest-bridge", the recommended and most restricted level of
propagation. See LLDP= above for an option to enable LLDP reception.

BindCarrier=
A link name or a list of link names. When set, controls the behavior of the current
link. When all links in the list are in an operational down state, the current link is
brought down. When at least one link has carrier, the current interface is brought up.

Address=
A static IPv4 or IPv6 address and its prefix length, separated by a "/" character.
Specify this key more than once to configure several addresses. The format of the
address must be as described in inet_pton(3). This is a short-hand for an [Address]
section only containing an Address key (see below). This option may be specified more
than once.

If the specified address is 0.0.0.0 (for IPv4) or [::] (for IPv6), a new address range
of the requested size is automatically allocated from a system-wide pool of unused
ranges. The allocated range is checked against all current network interfaces and all
known network configuration files to avoid address range conflicts. The default
system-wide pool consists of 192.168.0.0/16, 172.16.0.0/12 and 10.0.0.0/8 for IPv4,
and fc00::/7 for IPv6. This functionality is useful to manage a large number of
dynamically created network interfaces with the same network configuration and
automatic address range assignment.

Gateway=
The gateway address, which must be in the format described in inet_pton(3). This is a
short-hand for a [Route] section only containing a Gateway key. This option may be
specified more than once.

DNS=
A DNS server address, which must be in the format described in inet_pton(3). This
option may be specified more than once. This setting is read by systemd-
resolved.service(8).

Domains=
A list of domains which should be resolved using the DNS servers on this link. Each
item in the list should be a domain name, optionally prefixed with a tilde ("~"). The
domains with the prefix are called "routing-only domains". The domains without the
prefix are called "search domains" and are first used as search suffixes for extending
single-label host names (host names containing no dots) to become fully qualified
domain names (FQDNs). If a single-label host name is resolved on this interface, each
of the specified search domains are appended to it in turn, converting it into a fully
qualified domain name, until one of them may be successfully resolved.

Both "search" and "routing-only" domains are used for routing of DNS queries: look-ups
for host names ending in those domains (hence also single label names, if any "search
domains" are listed), are routed to the DNS servers configured for this interface. The
domain routing logic is particularly useful on multi-homed hosts with DNS servers
serving particular private DNS zones on each interface.

The "routing-only" domain "~." (the tilde indicating definition of a routing domain,
the dot referring to the DNS root domain which is the implied suffix of all valid DNS
names) has special effect. It causes all DNS traffic which does not match another
configured domain routing entry to be routed to DNS servers specified for this
interface. This setting is useful to prefer a certain set of DNS servers if a link on
which they are connected is available.

This setting is read by systemd-resolved.service(8). "Search domains" correspond to
the domain and search entries in resolv.conf(5). Domain name routing has no equivalent
in the traditional glibc API, which has no concept of domain name servers limited to a
specific link.

NTP=
An NTP server address. This option may be specified more than once. This setting is
read by systemd-timesyncd.service(8).

IPForward=
Configures IP packet forwarding for the system. If enabled, incoming packets on any
network interface will be forwarded to any other interfaces according to the routing
table. Takes either a boolean argument, or the values "ipv4" or "ipv6", which only
enable IP packet forwarding for the specified address family. This controls the
net.ipv4.ip_forward and net.ipv6.conf.all.forwarding sysctl options of the network
interface (see ip-sysctl.txt[5] for details about sysctl options). Defaults to "no".

Note: this setting controls a global kernel option, and does so one way only: if a
network that has this setting enabled is set up the global setting is turned on.
However, it is never turned off again, even after all networks with this setting
enabled are shut down again.

To allow IP packet forwarding only between specific network interfaces use a firewall.

IPMasquerade=
Configures IP masquerading for the network interface. If enabled, packets forwarded
from the network interface will be appear as coming from the local host. Takes a
boolean argument. Implies IPForward=ipv4. Defaults to "no".

IPv6PrivacyExtensions=
Configures use of stateless temporary addresses that change over time (see RFC
4941[6], Privacy Extensions for Stateless Address Autoconfiguration in IPv6). Takes a
boolean or the special values "prefer-public" and "kernel". When true, enables the
privacy extensions and prefers temporary addresses over public addresses. When
"prefer-public", enables the privacy extensions, but prefers public addresses over
temporary addresses. When false, the privacy extensions remain disabled. When
"kernel", the kernel's default setting will be left in place. Defaults to "no".

IPv6AcceptRA=
Enable or disable IPv6 Router Advertisement (RA) reception support for the interface.
Takes a boolean parameter. If true, RAs are accepted; if false, RAs are ignored,
independently of the local forwarding state. When not set, the kernel default is used,
and RAs are accepted only when local forwarding is disabled for that interface. When
RAs are accepted, they may trigger the start of the DHCPv6 client if the relevant
flags are set in the RA data, or if no routers are found on the link.

Further settings for the IPv6 RA support may be configured in the "[IPv6AcceptRA]"
section, see below.

Also see ip-sysctl.txt[5] in the kernel documentation regarding "accept_ra", but note
that systemd's setting of 1 (i.e. true) corresponds to kernel's setting of 2.

IPv6DuplicateAddressDetection=
Configures the amount of IPv6 Duplicate Address Detection (DAD) probes to send.
Defaults to unset.

IPv6HopLimit=
Configures IPv6 Hop Limit. For each router that forwards the packet, the hop limit is
decremented by 1. When the hop limit field reaches zero, the packet is discarded.
Defaults to unset.

IPv4ProxyARP=
A boolean. Configures proxy ARP for IPv4. Proxy ARP is the technique in which one
host, usually a router, answers ARP requests intended for another machine. By "faking"
its identity, the router accepts responsibility for routing packets to the "real"
destination. (see RFC 1027[7]. Defaults to unset.

IPv6ProxyNDP=
A boolean. Configures proxy NDP for IPv6. Proxy NDP (Neighbor Discovery Protocol) is a
technique for IPv6 to allow routing of addresses to a different destination when peers
expect them to be present on a certain physical link. In this case a router answers
Neighbour Advertisement messages intended for another machine by offering its own MAC
address as destination. Unlike proxy ARP for IPv4, it is not enabled globally, but
will only send Neighbour Advertisement messages for addresses in the IPv6 neighbor
proxy table, which can also be shown by ip -6 neighbour show proxy. systemd-networkd
will control the per-interface `proxy_ndp` switch for each configured interface
depending on this option. Defautls to unset.

IPv6ProxyNDPAddress=
An IPv6 address, for which Neighbour Advertisement messages will be proxied. This
option may be specified more than once. systemd-networkd will add the
IPv6ProxyNDPAddress= entries to the kernel's IPv6 neighbor proxy table. This option
implies IPv6ProxyNDP=true but has no effect if IPv6ProxyNDP has been set to false.
Defaults to unset.

IPv6PrefixDelegation=
Whether to enable or disable Router Advertisement sending on a link. Allowed values
are "static" which distributes prefixes as defined in the "[IPv6PrefixDelegation]" and
any "[IPv6Prefix]" sections, "dhcpv6" which requests prefixes using a DHCPv6 client
configured for another link and any values configured in the "[IPv6PrefixDelegation]"
section while ignoring all static prefix configuration sections, "yes" which uses both
static configuration and DHCPv6, and "false" which turns off IPv6 prefix delegation
altogether. Defaults to "false". See the "[IPv6PrefixDelegation]" and the
"[IPv6Prefix]" sections for more configuration options.

Bridge=
The name of the bridge to add the link to. See systemd.netdev(5).

Bond=
The name of the bond to add the link to. See systemd.netdev(5).

VRF=
The name of the VRF to add the link to. See systemd.netdev(5).

VLAN=
The name of a VLAN to create on the link. See systemd.netdev(5). This option may be
specified more than once.

MACVLAN=
The name of a MACVLAN to create on the link. See systemd.netdev(5). This option may be
specified more than once.

VXLAN=
The name of a VXLAN to create on the link. See systemd.netdev(5). This option may be
specified more than once.

Tunnel=
The name of a Tunnel to create on the link. See systemd.netdev(5). This option may be
specified more than once.

ActiveSlave=
A boolean. Specifies the new active slave. The "ActiveSlave=" option is only valid for
following modes: "active-backup", "balance-alb" and "balance-tlb". Defaults to false.

PrimarySlave=
A boolean. Specifies which slave is the primary device. The specified device will
always be the active slave while it is available. Only when the primary is off-line
will alternate devices be used. This is useful when one slave is preferred over
another, e.g. when one slave has higher throughput than another. The "PrimarySlave="
option is only valid for following modes: "active-backup", "balance-alb" and
"balance-tlb". Defaults to false.

ConfigureWithoutCarrier=
A boolean. Allows networkd to configure a specific link even if it has no carrier.
Defaults to false.

[Address] Section

An "[Address]" section accepts the following keys. Specify several "[Address]" sections to
configure several addresses.

Address=
As in the "[Network]" section. This key is mandatory.

Peer=
The peer address in a point-to-point connection. Accepts the same format as the
"Address" key.

Broadcast=
The broadcast address, which must be in the format described in inet_pton(3). This key
only applies to IPv4 addresses. If it is not given, it is derived from the "Address"
key.

Label=
An address label.

PreferredLifetime=
Allows the default "preferred lifetime" of the address to be overridden. Only three
settings are accepted: "forever" or "infinity" which is the default and means that the
address never expires, and "0" which means that the address is considered immediately
"expired" and will not be used, unless explicitly requested. A setting of
PreferredLifetime=0 is useful for addresses which are added to be used only by a
specific application, which is then configured to use them explicitly.

Scope=
The scope of the address, which can be "global", "link" or "host" or an unsigned
integer ranges 0 to 255. Defaults to "global".

HomeAddress=
Takes a boolean argument. Designates this address the "home address" as defined in RFC
6275[8]. Supported only on IPv6. Defaults to false.

DuplicateAddressDetection=
Takes a boolean argument. Do not perform Duplicate Address Detection RFC 4862[9] when
adding this address. Supported only on IPv6. Defaults to false.

ManageTemporaryAddress=
Takes a boolean argument. If true the kernel manage temporary addresses created from
this one as template on behalf of Privacy Extensions RFC 3041[10]. For this to become
active, the use_tempaddr sysctl setting has to be set to a value greater than zero.
The given address needs to have a prefix length of 64. This flag allows to use privacy
extensions in a manually configured network, just like if stateless auto-configuration
was active. Defaults to false.

PrefixRoute=
Takes a boolean argument. When adding or modifying an IPv6 address, the userspace
application needs a way to suppress adding a prefix route. This is for example
relevant together with IFA_F_MANAGERTEMPADDR, where userspace creates autoconf
generated addresses, but depending on on-link, no route for the prefix should be
added. Defaults to false.

AutoJoin=
Takes a boolean argument. Joining multicast group on ethernet level via ip maddr
command would not work if we have an Ethernet switch that does IGMP snooping since the
switch would not replicate multicast packets on ports that did not have IGMP reports
for the multicast addresses. Linux vxlan interfaces created via ip link add vxlan or
networkd's netdev kind vxlan have the group option that enables then to do the
required join. By extending ip address command with option "autojoin" we can get
similar functionality for openvswitch (OVS) vxlan interfaces as well as other
tunneling mechanisms that need to receive multicast traffic. Defaults to "no".

[IPV6ADDRESSLABEL] SECTION OPTIONS
An "[IPv6AddressLabel]" section accepts the following keys. Specify several
"[IPv6AddressLabel]" sections to configure several address labels. IPv6 address labels are
used for address selection. See RFC 3484[11]. Precedence is managed by userspace, and only
the label itself is stored in the kernel

Label=
The label for the prefix (an unsigned integer) ranges 0 to 4294967294. 0xffffffff is
reserved. This key is mandatory.

Prefix=
IPv6 prefix is an address with a prefix length, separated by a slash "/" character.
This key is mandatory.

[RoutingPolicyRule] Section

 An "[RoutingPolicyRule]" section accepts the following keys. Specify several
       "[RoutingPolicyRule]" sections to configure several rules.

       TypeOfService=
           Specifies the type of service to match a number between 0 to 255.

       From=
           Specifies the source address prefix to match. Possibly followed by a slash and the
           prefix length.

       To=
           Specifies the destination address prefix to match. Possibly followed by a slash and
           the prefix length.

       FirewallMark=
           Specifies the iptables firewall mark value to match (a number between 1 and
           4294967295).

       Table=
           Specifies the routing table identifier to lookup if the rule selector matches. The
           table identifier for a route (a number between 1 and 4294967295).

       Priority=
           Specifies the priority of this rule.  Priority= is an unsigned integer. Higher number
           means lower priority, and rules get processed in order of increasing number.

       IncomingInterface=
           Specifies incoming device to match. If the interface is loopback, the rule only
           matches packets originating from this host.

       OutgoingInterface=
           Specifies the outgoing device to match. The outgoing interface is only available for
           packets originating from local sockets that are bound to a device.

[Route] Section

The "[Route]" section accepts the following keys. Specify several "[Route]" sections to
configure several routes.

Gateway=
As in the "[Network]" section.

GatewayOnlink=
The "GatewayOnlink" option tells the kernel that it does not have to check if the
gateway is reachable directly by the current machine (i.e., the kernel does not need
to check if the gateway is attached to the local network), so that we can insert the
route in the kernel table without it being complained about. A boolean, defaults to
"no".

Destination=
The destination prefix of the route. Possibly followed by a slash and the prefix
length. If omitted, a full-length host route is assumed.

Source=
The source prefix of the route. Possibly followed by a slash and the prefix length. If
omitted, a full-length host route is assumed.

Metric=
The metric of the route (an unsigned integer).

IPv6Preference=
Specifies the route preference as defined in RFC4191[12] for Router Discovery
messages. Which can be one of "low" the route has a lowest priority, "medium" the
route has a default priority or "high" the route has a highest priority.

Scope=
The scope of the route, which can be "global", "link" or "host". Defaults to "global".

PreferredSource=
The preferred source address of the route. The address must be in the format described
in inet_pton(3).

Table=num
The table identifier for the route (a number between 1 and 4294967295, or 0 to unset).
The table can be retrieved using ip route show table num.

Protocol=
The Protocol identifier for the route. Takes a number between 0 and 255 or the special
values "kernel", "boot" and "static". Defaults to "static".

Type=
The Type identifier for special route types, which can be "unicast" route to a
destination network address which describes the path to the destination, "blackhole"
packets are discarded silently, "unreachable" packets are discarded and the ICMP
message host unreachable is generated, "prohibit" packets are discarded and the ICMP
message communication administratively prohibited is generated. Defaults to "unicast".

InitialCongestionWindow=
The TCP initial congestion window is used during the start of a TCP connection. During
the start of a TCP session, when a client requests a resource, the server's initial
congestion window determines how many data bytes will be sent during the initial burst
of data. Takes a size in bytes between 1 and 4294967295 (2^32 - 1). The usual suffixes
K, M, G are supported and are understood to the base of 1024. Defaults to unset.

InitialAdvertisedReceiveWindow=
The TCP initial advertised receive window is the amount of receive data (in bytes)
that can initally be buffered at one time on a connection. The sending host can send
only that amount of data before waiting for an acknowledgment and window update from
the receiving host. Takes a size in bytes between 1 and 4294967295 (2^32 - 1). The
usual suffixes K, M, G are supported and are understood to the base of 1024. Defaults
to unset.

QuickAck=
Takes a boolean argument. When true enables TCP quick ack mode for the route. Defaults
to unset.

[DHCP] section

The "[DHCP]" section configures the DHCPv4 and DHCP6 client, if it is enabled with the
DHCP= setting described above:

UseDNS=
When true (the default), the DNS servers received from the DHCP server will be used
and take precedence over any statically configured ones.

This corresponds to the nameserver option in resolv.conf(5).

UseNTP=
When true (the default), the NTP servers received from the DHCP server will be used by
systemd-timesyncd and take precedence over any statically configured ones.

UseMTU=
When true, the interface maximum transmission unit from the DHCP server will be used
on the current link. Defaults to false.

Anonymize=
Takes a boolean argument. When true, the options sent to the DHCP server will follow
the RFC 7844[13] (Anonymity Profiles for DHCP Clients) to minimize disclosure of
identifying information. Defaults to false.

This option should only be set to true when MACAddressPolicy= is set to "random" (see
systemd.link(5)).

Note that this configuration will overwrite others. In concrete, the following
variables will be ignored: SendHostname=, ClientIdentifier=, UseRoutes=,
SendHostname=, UseMTU=, VendorClassIdentifier=, UseTimezone=.

SendHostname=
When true (the default), the machine's hostname will be sent to the DHCP server.

UseHostname=
When true (the default), the hostname received from the DHCP server will be set as the
transient hostname of the system

Hostname=
Use this value for the hostname which is sent to the DHCP server, instead of machine's
hostname.

UseDomains=
Takes a boolean argument, or the special value "route". When true, the domain name
received from the DHCP server will be used as DNS search domain over this link,
similar to the effect of the Domains= setting. If set to "route", the domain name
received from the DHCP server will be used for routing DNS queries only, but not for
searching, similar to the effect of the Domains= setting when the argument is prefixed
with "~". Defaults to true on Ubuntu.

It is recommended to enable this option only on trusted networks, as setting this
affects resolution of all host names, in particular of single-label names. It is
generally safer to use the supplied domain only as routing domain, rather than as
search domain, in order to not have it affect local resolution of single-label names.

When set to true, this setting corresponds to the domain option in resolv.conf(5).

UseRoutes=
When true (the default), the static routes will be requested from the DHCP server and
added to the routing table with a metric of 1024, and a scope of "global", "link" or
"host", depending on the route's destination and gateway. If the destination is on the
local host, e.g., 127.x.x.x, or the same as the link's own address, the scope will be
set to "host". Otherwise if the gateway is null (a direct route), a "link" scope will
be used. For anything else, scope defaults to "global".

UseTimezone=
When true, the timezone received from the DHCP server will be set as timezone of the
local system. Defaults to "no".

CriticalConnection=
When true, the connection will never be torn down even if the DHCP lease expires. This
is contrary to the DHCP specification, but may be the best choice if, say, the root
filesystem relies on this connection. Defaults to false.

ClientIdentifier=
The DHCPv4 client identifier to use. Either "mac" to use the MAC address of the link
or "duid" (the default, see below) to use an RFC4361-compliant Client ID.

VendorClassIdentifier=
The vendor class identifier used to identify vendor type and configuration.

DUIDType=
Override the global DUIDType setting for this network. See networkd.conf(5) for a
description of possible values.

DUIDRawData=
Override the global DUIDRawData setting for this network. See networkd.conf(5) for a
description of possible values.

IAID=
The DHCP Identity Association Identifier (IAID) for the interface, a 32-bit unsigned
integer.

RequestBroadcast=
Request the server to use broadcast messages before the IP address has been
configured. This is necessary for devices that cannot receive RAW packets, or that
cannot receive packets at all before an IP address has been configured. On the other
hand, this must not be enabled on networks where broadcasts are filtered out.

RouteMetric=
Set the routing metric for routes specified by the DHCP server.

RouteTable=num
The table identifier for DHCP routes (a number between 1 and 4294967295, or 0 to
unset). The table can be retrieved using ip route show table num.

When used in combination with VRF= the VRF's routing table is used unless this
parameter is specified.

ListenPort=
Allow setting custom port for the DHCP client to listen on.

RapidCommit=
A boolean. The DHCPv6 client can obtain configuration parameters from a DHCPv6 server
through a rapid two-message exchange (solicit and reply). When the rapid commit option
is enabled by both the DHCPv6 client and the DHCPv6 server, the two-message exchange
is used, rather than the default four-method exchange (solicit, advertise, request,
and reply). The two-message exchange provides faster client configuration and is
beneficial in environments in which networks are under a heavy load. See RFC 3315[14]
for details. Defaults to true.

[IPv6Acceptra] Section

The "[IPv6AcceptRA]" section configures the IPv6 Router Advertisement (RA) client, if it
is enabled with the IPv6AcceptRA= setting described above:

UseDNS=
When true (the default), the DNS servers received in the Router Advertisement will be
used and take precedence over any statically configured ones.

This corresponds to the nameserver option in resolv.conf(5).

UseDomains=
Takes a boolean argument, or the special value "route". When true, the domain name
received via IPv6 Router Advertisement (RA) will be used as DNS search domain over
this link, similar to the effect of the Domains= setting. If set to "route", the
domain name received via IPv6 RA will be used for routing DNS queries only, but not
for searching, similar to the effect of the Domains= setting when the argument is
prefixed with "~". Defaults to true on Ubuntu.

It is recommended to enable this option only on trusted networks, as setting this
affects resolution of all host names, in particular of single-label names. It is
generally safer to use the supplied domain only as routing domain, rather than as
search domain, in order to not have it affect local resolution of single-label names.

When set to true, this setting corresponds to the domain option in resolv.conf(5).

RouteTable=num
The table identifier for the routes received in the Router Advertisement (a number
between 1 and 4294967295, or 0 to unset). The table can be retrieved using ip route
show table num.

[DHCPServer] Section

The "[DHCPServer]" section contains settings for the DHCP server, if enabled via the
DHCPServer= option described above:

PoolOffset=, PoolSize=
Configures the pool of addresses to hand out. The pool is a contiguous sequence of IP
addresses in the subnet configured for the server address, which does not include the
subnet nor the broadcast address. PoolOffset= takes the offset of the pool from the
start of subnet, or zero to use the default value. PoolSize= takes the number of IP
addresses in the pool or zero to use the default value. By default, the pool starts at
the first address after the subnet address and takes up the rest of the subnet,
excluding the broadcast address. If the pool includes the server address (the
default), this is reserved and not handed out to clients.

DefaultLeaseTimeSec=, MaxLeaseTimeSec=
Control the default and maximum DHCP lease time to pass to clients. These settings
take time values in seconds or another common time unit, depending on the suffix. The
default lease time is used for clients that did not ask for a specific lease time. If
a client asks for a lease time longer than the maximum lease time, it is automatically
shortened to the specified time. The default lease time defaults to 1h, the maximum
lease time to 12h. Shorter lease times are beneficial if the configuration data in
DHCP leases changes frequently and clients shall learn the new settings with shorter
latencies. Longer lease times reduce the generated DHCP network traffic.

EmitDNS=, DNS=
Configures whether the DHCP leases handed out to clients shall contain DNS server
information. The EmitDNS= setting takes a boolean argument and defaults to "yes". The
DNS servers to pass to clients may be configured with the DNS= option, which takes a
list of IPv4 addresses. If the EmitDNS= option is enabled but no servers configured,
the servers are automatically propagated from an "uplink" interface that has
appropriate servers set. The "uplink" interface is determined by the default route of
the system with the highest priority. Note that this information is acquired at the
time the lease is handed out, and does not take uplink interfaces into account that
acquire DNS or NTP server information at a later point. DNS server propagation does
not take /etc/resolv.conf into account. Also, note that the leases are not refreshed
if the uplink network configuration changes. To ensure clients regularly acquire the
most current uplink DNS server information, it is thus advisable to shorten the DHCP
lease time via MaxLeaseTimeSec= described above.

EmitNTP=, NTP=
Similar to the EmitDNS= and DNS= settings described above, these settings configure
whether and what NTP server information shall be emitted as part of the DHCP lease.
The same syntax, propagation semantics and defaults apply as for EmitDNS= and DNS=.

EmitRouter=
Similar to the EmitDNS= setting described above, this setting configures whether the
DHCP lease should contain the router option. The same syntax, propagation semantics
and defaults apply as for EmitDNS=.

EmitTimezone=, Timezone=
Configures whether the DHCP leases handed out to clients shall contain timezone
information. The EmitTimezone= setting takes a boolean argument and defaults to "yes".
The Timezone= setting takes a timezone string (such as "Europe/Berlin" or "UTC") to
pass to clients. If no explicit timezone is set, the system timezone of the local host
is propagated, as determined by the /etc/localtime symlink.

[IPv6PrefixDelegation] section

The "[IPv6PrefixDelegation]" section contains settings for sending IPv6 Router
Advertisements and whether to act as a router, if enabled via the IPv6PrefixDelegation=
option described above. IPv6 network prefixes are defined with one or more "[IPv6Prefix]"
sections.

Managed=, OtherInformation=
Controls whether a DHCPv6 server is used to acquire IPv6 addresses on the network link
when Managed= boolean is set to "true" or if only additional network information can
be obtained via DHCPv6 for the network link when OtherInformation= boolean is set to
"true". Both settings default to "false", which means that a DHCPv6 server is not
being used.

RouterLifetimeSec=
Configures the IPv6 router lifetime in seconds. If set, this host also announces
itself in Router Advertisements as an IPv6 router for the network link. Defaults to
unset, which means the host is not acting as a router.

RouterPreference=
Configures IPv6 router preference if RouterLifetimeSec= is non-zero. Valid values are
"high", "medium" and "low", with "normal" and "default" added as synonyms for "medium"
just to make configuration easier. See RFC 4191[12] for details. Defaults to "medium".

EmitDNS=, DNS=
DNS= specifies a list of recursive DNS server IPv6 addresses that distributed via
Router Advertisement messages when EmitDNS= is true. If DNS= is empty, DNS servers are
read from the "[Network]" section. If the "[Network]" section does not contain any DNS
servers either, DNS servers from the uplink with the highest priority default route
are used. When EmitDNS= is false, no DNS server information is sent in Router
Advertisement messages. EmitDNS= defaults to true.

EmitDomains=, Domains=
A list of DNS search domains distributed via Router Advertisement messages when
EmitDomains= is true. If Domains= is empty, DNS search domains are read from the
"[Network]" section. If the "[Network]" section does not contain any DNS search
domains either, DNS search domains from the uplink with the highest priority default
route are used. When EmitDomains= is false, no DNS search domain information is sent
in Router Advertisement messages. EmitDomains= defaults to true.

DNSLifetimeSec=
Lifetime in seconds for the DNS server addresses listed in DNS= and search domains
listed in Domains=.

[IPv6Prefix] Section

  One or more "[IPv6Prefix]" sections contain the IPv6 prefixes that are announced via
       Router Advertisements. See RFC 4861[15] for further details.

       AddressAutoconfiguration=, OnLink=
           Boolean values to specify whether IPv6 addresses can be autoconfigured with this
           prefix and whether the prefix can be used for onlink determination. Both settings
           default to "true" in order to ease configuration.

       Prefix=
           The IPv6 prefix that is to be distributed to hosts. Similarly to configuring static
           IPv6 addresses, the setting is configured as an IPv6 prefix and its prefix length,
           separated by a "/" character. Use multiple "[IPv6Prefix]" sections to configure
           multiple IPv6 prefixes since prefix lifetimes, address autoconfiguration and onlink
           status may differ from one prefix to another.

       PreferredLifetimeSec=, ValidLifetimeSec=
           Preferred and valid lifetimes for the prefix measured in seconds.
           PreferredLifetimeSec= defaults to 604800 seconds (one week) and ValidLifetimeSec=
           defaults to 2592000 seconds (30 days).

[Bridge] Section

The "[Bridge]" section accepts the following keys.

UnicastFlood=
A boolean. Controls whether the bridge should flood traffic for which an FDB entry is
missing and the destination is unknown through this port. Defaults to on.

HairPin=
A boolean. Configures whether traffic may be sent back out of the port on which it was
received. By default, this flag is false, and the bridge will not forward traffic back
out of the receiving port.

UseBPDU=
A boolean. Configures whether STP Bridge Protocol Data Units will be processed by the
bridge port. Defaults to yes.

FastLeave=
A boolean. This flag allows the bridge to immediately stop multicast traffic on a port
that receives an IGMP Leave message. It is only used with IGMP snooping if enabled on
the bridge. Defaults to off.

AllowPortToBeRoot=
A boolean. Configures whether a given port is allowed to become a root port. Only used
when STP is enabled on the bridge. Defaults to on.

Cost=
Sets the "cost" of sending packets of this interface. Each port in a bridge may have a
different speed and the cost is used to decide which link to use. Faster interfaces
should have lower costs. It is an integer value between 1 and 65535.

Priority=
Sets the "priority" of sending packets on this interface. Each port in a bridge may
have a different priority which is used to decide which link to use. Lower value means
higher priority. It is an integer value between 0 to 63. Networkd does not set any
default, meaning the kernel default value of 32 is used.

[BridgeFDB] section

 The "[BridgeFDB]" section manages the forwarding database table of a port and accepts the
       following keys. Specify several "[BridgeFDB]" sections to configure several static MAC
       table entries.

       MACAddress=
           As in the "[Network]" section. This key is mandatory.

       VLANId=
           The VLAN ID for the new static MAC table entry. If omitted, no VLAN ID information is
           appended to the new static MAC table entry.

[BridgeVLAN] section

The "[BridgeVLAN]" section manages the VLAN ID configuration of a bridge port and accepts
       the following keys. Specify several "[BridgeVLAN]" sections to configure several VLAN
       entries. The VLANFiltering= option has to be enabled, see "[Bridge]" section in
       systemd.netdev(5).

       VLAN=
           The VLAN ID allowed on the port. This can be either a single ID or a range M-N. VLAN
           IDs are valid from 1 to 4094.

       EgressUntagged=
           The VLAN ID specified here will be used to untag frames on egress. Configuring
           EgressUntagged= implicates the use of VLAN= above and will enable the VLAN ID for
           ingress as well. This can be either a single ID or a range M-N.

       PVID=
           The Port VLAN ID specified here is assigned to all untagged frames at ingress.  PVID=
           can be used only once. Configuring PVID= implicates the use of VLAN= above and will
           enable the VLAN ID for ingress as well.

Examples

       Example 1. Static network configuration

           # /etc/systemd/network/50-static.network
           [Match]
           Name=enp2s0

           [Network]
           Address=192.168.0.15/24
           Gateway=192.168.0.1

       This brings interface "enp2s0" up with a static address. The specified gateway will be
       used for a default route.

       Example 2. DHCP on ethernet links

           # /etc/systemd/network/80-dhcp.network
           [Match]
           Name=en*

           [Network]
           DHCP=yes

       This will enable DHCPv4 and DHCPv6 on all interfaces with names starting with "en" (i.e.
       ethernet interfaces).

       Example 3. A bridge with two enslaved links

           # /etc/systemd/network/25-bridge-static.network
           [Match]
           Name=bridge0

           [Network]
           Address=192.168.0.15/24
           Gateway=192.168.0.1
           DNS=192.168.0.1

           # /etc/systemd/network/25-bridge-slave-interface-1.network
           [Match]
           Name=enp2s0

           [Network]
           Bridge=bridge0

           # /etc/systemd/network/25-bridge-slave-interface-2.network
           [Match]
           Name=wlp3s0

           [Network]
           Bridge=bridge0

       This creates a bridge and attaches devices "enp2s0" and "wlp3s0" to it. The bridge will
       have the specified static address and network assigned, and a default route via the
       specified gateway will be added. The specified DNS server will be added to the global list
       of DNS resolvers.

       Example 4.

           # /etc/systemd/network/20-bridge-slave-interface-vlan.network
           [Match]
           Name=enp2s0

           [Network]
           Bridge=bridge0

           [BridgeVLAN]
           VLAN=1-32
           PVID=42
           EgressUntagged=42

           [BridgeVLAN]
           VLAN=100-200

           [BridgeVLAN]
           EgressUntagged=300-400

       This overrides the configuration specified in the previous example for the interface
       "enp2s0", and enables VLAN on that bridge port. VLAN IDs 1-32, 42, 100-400 will be
       allowed. Packets tagged with VLAN IDs 42, 300-400 will be untagged when they leave on this
       interface. Untagged packets which arrive on this interface will be assigned VLAN ID 42.

       Example 5. Various tunnels

           /etc/systemd/network/25-tunnels.network
           [Match]
           Name=ens1

           [Network]
           Tunnel=ipip-tun
           Tunnel=sit-tun
           Tunnel=gre-tun
           Tunnel=vti-tun

           /etc/systemd/network/25-tunnel-ipip.netdev
           [NetDev]
           Name=ipip-tun
           Kind=ipip

           /etc/systemd/network/25-tunnel-sit.netdev
           [NetDev]
           Name=sit-tun
           Kind=sit

           /etc/systemd/network/25-tunnel-gre.netdev
           [NetDev]
           Name=gre-tun
           Kind=gre

           /etc/systemd/network/25-tunnel-vti.netdev
           [NetDev]
           Name=vti-tun
           Kind=vti

       This will bring interface "ens1" up and create an IPIP tunnel, a SIT tunnel, a GRE tunnel,
       and a VTI tunnel using it.

       Example 6. A bond device

           # /etc/systemd/network/30-bond1.network
           [Match]
           Name=bond1

           [Network]
           DHCP=ipv6

           # /etc/systemd/network/30-bond1.netdev
           [NetDev]
           Name=bond1
           Kind=bond

           # /etc/systemd/network/30-bond1-dev1.network
           [Match]
           MACAddress=52:54:00:e9:64:41

           [Network]
           Bond=bond1

           # /etc/systemd/network/30-bond1-dev2.network
           [Match]
           MACAddress=52:54:00:e9:64:42

           [Network]
           Bond=bond1

       This will create a bond device "bond1" and enslave the two devices with MAC addresses
       52:54:00:e9:64:41 and 52:54:00:e9:64:42 to it. IPv6 DHCP will be used to acquire an
       address.

       Example 7. Virtual Routing and Forwarding (VRF)

       Add the "bond1" interface to the VRF master interface "vrf1". This will redirect routes
       generated on this interface to be within the routing table defined during VRF creation.
       For kernels before 4.8 traffic won't be redirected towards the VRFs routing table unless
       specific ip-rules are added.

           # /etc/systemd/network/25-vrf.network
           [Match]
           Name=bond1

           [Network]
           VRF=vrf1

       Example 8. MacVTap

       This brings up a network interface "macvtap-test" and attaches it to "enp0s25".

           # /lib/systemd/network/25-macvtap.network
           [Match]
           Name=enp0s25

           [Network]
           MACVTAP=macvtap-test