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OVS-ACTIONS(7) Open vSwitch OVS-ACTIONS(7)
ovs-actions - OpenFlow actions and instructions with Open vSwitch
extensions
This document aims to comprehensively document all of the OpenFlow
actions and instructions, both standard and non-standard,
supported by Open vSwitch, regardless of origin. The document
includes information of interest to Open vSwitch users, such as
the semantics of each supported action and the syntax used by Open
vSwitch tools, and to developers seeking to build controllers and
switches compatible with Open vSwitch, such as the wire format for
each supported message.
Actions
In this document, we define an action as an OpenFlow action, which
is a kind of command that specifies what to do with a packet.
Actions are used in OpenFlow flows to describe what to do when the
flow matches a packet, and in a few other places in OpenFlow.
Each version of the OpenFlow specification defines standard
actions, and beyond that many OpenFlow switches, including Open
vSwitch, implement extensions to the standard.
OpenFlow groups actions in two ways: as an action list or an
action set, described below.
Action Lists
An action list, a concept present in every version of OpenFlow, is
simply an ordered sequence of actions. The OpenFlow
specifications require a switch to execute actions within an
action list in the order specified, and to refuse to execute an
action list entirely if it cannot implement the actions in that
order [OpenFlow 1.0, section 3.3], with one exception: when an
action list outputs multiple packets, the switch may output the
packets in an order different from that specified. Usually, this
exception is not important, especially in the common case when the
packets are output to different ports.
Action Sets
OpenFlow 1.1 introduced the concept of an action set. An action
set is also a sequence of actions, but the switch reorders the
actions and drops duplicates according to rules specified in the
OpenFlow specifications. Because of these semantics, some
standard OpenFlow actions cannot usefully be included in an action
set. For some, but not all, Open vSwitch extension actions, Open
vSwitch defines its own action set semantics and ordering.
The OpenFlow pipeline has an action set associated with it as a
packet is processed. After pipeline processing is otherwise
complete, the switch executes the actions in the action set.
Open vSwitch applies actions in an action set in the following
order: Except as noted otherwise below, the action set only
executes at most a single action of each type, and when more than
one action of a given type is present, the one added to the set
later replaces the earlier action:
1. strip_vlan
2. pop_mpls
3. decap
4. encap
5. push_mpls
6. push_vlan
7. dec_ttl
8. dec_mpls_ttl
9. dec_nsh_ttl
10. All of the following actions are executed in the order
added to the action set, with cumulative effect. That is,
when multiple actions modify the same part of a field, the
later modification takes effect, and when they modify
different parts of a field (or different fields), then both
modifications are applied:
• load
• move
• mod_dl_dst
• mod_dl_src
• mod_nw_dst
• mod_nw_src
• mod_nw_tos
• mod_nw_ecn
• mod_nw_ttl
• mod_tp_dst
• mod_tp_src
• mod_vlan_pcp
• mod_vlan_vid
• set_field
• set_tunnel
• set_tunnel64
11. set_queue
12. group, output, resubmit, ct_clear, or ct. If more than one
of these actions is present, then the one listed earliest
above is executed and the others are ignored, regardless of
the order in which they were added to the action set. (If
none of these actions is present, the action set has no
real effect, because the modified packet is not sent
anywhere and thus the modifications are not visible.)
An action set may only contain the actions listed above.
Error Handling
Packet processing can encounter a variety of errors:
Bridge not found
Open vSwitch supports an extension to the standard OpenFlow
controller action called a continuation, which allows the
controller to interrupt and later resume the processing of
a packet through the switch pipeline. This error occurs
when such a packet’s processing cannot be resumed, e.g.
because the bridge processing it has been destroyed. Open
vSwitch reports this error to the controller as Open
vSwitch extension error NXR_STALE.
This error prevents packet processing entirely.
Recursion too deep
While processing a given packet, Open vSwitch limits the
flow table recursion depth to 64, to ensure that packet
processing uses a finite amount of time and space. Actions
that count against the recursion limit include resubmit
from a given OpenFlow table to the same or an earlier
table, group, and output to patch ports.
A resubmit from one table to a later one (or, equivalently,
a goto_table instruction) does not count against the depth
limit because resubmits to strictly monotonically
increasing tables will eventually terminate. OpenFlow
tables are most commonly traversed in numerically
increasing order, so this limit has little effect on
conventionally designed OpenFlow pipelines.
This error terminates packet processing. Any previous side
effects (e.g. output actions) are retained.
Usually this error indicates a loop or other bug in the
OpenFlow flow tables. To assist debugging, when this error
occurs, Open vSwitch 2.10 and later logs a trace of the
packet execution, as if by ovs-appctl ofproto/trace,
rate-limited to one per minute to reduce the log volume.
Too many resubmits
Open vSwitch limits the total number of resubmit actions
that a given packet can execute to 4,096. For this
purpose, goto_table instructions and output to the table
port are treated like resubmit. This limits the amount of
time to process a single packet.
Unlike the limit on recursion depth, the limit on resubmits
counts all resubmits, regardless of direction.
This error has the same effect, including logging, as
exceeding the recursion depth limit.
Stack too deep
Open vSwitch limits the amount of data that the push action
can put onto the stack at one time to 64 kB of data.
This error terminates packet processing. Any previous side
effects (e.g. output actions) are retained.
No recirculation context / Recirculation conflict
These errors indicate internal errors inside Open vSwitch
and should generally not occur. If you notice recurring
log messages about these errors, please report a bug.
Too many MPLS labels
Open vSwitch can process packets with any number of MPLS
labels, but its ability to push and pop MPLS labels is
limited, currently to 3 labels. Attempting to push more
than the supported number of labels onto a packet, or to
pop any number of labels from a packet with more than the
supported number, raises this error.
This error terminates packet processing, retaining any
previous side effects (e.g. output actions). When this
error arises within the execution of a group bucket, it
only terminates that bucket’s execution, not packet
processing overall.
Invalid tunnel metadata
Open vSwitch raises this error when it processes a Geneve
packet that has TLV options with an invalid form, e.g.
where the length in a TLV would extend past the end of the
options.
This error prevents packet processing entirely.
Unsupported packet type
When a encap action encapsulates a packet, Open vSwitch
raises this error if it does not support the combination of
the new encapsulation with the current packet.
encap(ethernet) raises this error if the current packet is
not an L3 packet, and encap(nsh) raises this error if the
current packet is not Ethernet, IPv4, IPv6, or NSH.
The decap action is supported only for packet types
ethernet, NSH and MPLS. Openvswitch raises this error for
other packet types. When a decap action decapsulates a
packet, Open vSwitch raises this error if it does not
support the type of inner packet. decap of an Ethernet
header raises this error if a VLAN header is present, decap
of a NSH packet raises this error if the NSH inner packet
is not Ethernet, IPv4, IPv6, or NSH.
This error terminates packet processing, retaining any
previous side effects (e.g. output actions). When this
error arises within the execution of a group bucket, it
only terminates that bucket’s execution, not packet
processing overall.
Inconsistencies
OpenFlow 1.0 allows any action to be part of any flow, regardless
of the flow’s match. Some combinations do not make sense, e.g. an
set_nw_tos action in a flow that matches only ARP packets or
strip_vlan in a flow that matches packets without VLAN tags.
Other combinations have varying results depending on the kind of
packet that the flow processes, e.g. a set_nw_src action in a flow
that does not match on Ethertype will be treated as a no-op when
it processes a non-IPv4 packet. Nevertheless OVS allows all of
the above in conformance with OpenFlow 1.0, that is, the following
will succeed:
$ ovs-ofctl -O OpenFlow10 add-flow br0 arp,actions=mod_nw_tos:12
$ ovs-ofctl -O OpenFlow10 add-flow br0 dl_vlan=0xffff,actions=strip_vlan
$ ovs-ofctl -O OpenFlow10 add-flow br0 actions=mod_nw_src:1.2.3.4
Open vSwitch calls these kinds of combinations inconsistencies
between match and actions. OpenFlow 1.1 and later forbid
inconsistencies, and disallow the examples described above by
preventing such flows from being added. All of the above, for
example, will fail with an error message if one replaces
OpenFlow10 by OpenFlow11.
OpenFlow 1.1 and later cannot detect and disallow all
inconsistencies. For example, the write_actions instruction
arbitrarily delays execution of the actions inside it, which can
even be canceled with clear_actions, so that there is no way to
ensure that its actions are consistent with the packet at the time
they execute. Thus, actions with write_actions and some other
contexts are exempt from consistency requirements.
When OVS executes an action inconsistent with the packet, it
treats it as a no-op.
Inter-Version Compatibility
Open vSwitch supports multiple OpenFlow versions simultaneously on
a single switch. When actions are added with one OpenFlow version
and then retrieved with another, Open vSwitch does its best to
translate between them.
Inter-version compatibility issues can still arise when different
connections use different OpenFlow versions. Backward
compatibility is the most obvious case. Suppose, for example,
that an OpenFlow 1.1 session adds a flow with a push_vlan action,
for which there is no equivalent in OpenFlow 1.0. If an OpenFlow
1.0 session retrieves this flow, Open vSwitch must somehow
represent the action.
Forward compatibility can also be an issue, because later OpenFlow
versions sometimes remove functionality. The best example is the
enqueue action from OpenFlow 1.0, which OpenFlow 1.1 removed.
In practice, Open vSwitch uses a variety of strategies for
inter-version compatibility:
• Most standard OpenFlow actions, such as output actions,
translate without compatibility issues.
• Open vSwitch supports its extension actions in every OpenFlow
version, so they do not pose inter-version compatibility
problems.
• Open vSwitch sometimes adds extension actions to ensure backward
or forward compatibility. For example, for backward
compatibility with the group action added in OpenFlow 1.1, Open
vSwitch includes an OpenFlow 1.0 extension group action.
Perfect inter-version compatibility is not possible, so best
results require OpenFlow connections to use a consistent version.
One may enforce use of a particular version by setting the
protocols column for a bridge, e.g. to force br0 to use only
OpenFlow 1.3:
ovs-vsctl set bridge br0 protocols=OpenFlow13
Field Specifications
Many Open vSwitch actions refer to fields. In such cases, fields
may usually be referred to by their common names, such as eth_dst
for the Ethernet destination field, or by their full OXM or NXM
names, such as NXM_OF_ETH_DST or OXM_OF_ETH_DST. Before Open
vSwitch 2.7, only OXM or NXM field names were accepted.
Many actions that act on fields can also act on subfields, that
is, parts of fields, written as field[start..end], where start is
the first bit and end is the last bit to use in field, e.g.
vlan_tci[13..15] for the VLAN PCP. A single-bit subfield may also
be written as field[offset], e.g. vlan_tci[13] for the
least-significant bit of the VLAN PCP. Empty brackets may be used
to explicitly designate an entire field, e.g. vlan_tci[] for the
entire 16-bit VLAN TCI header. Before Open vSwitch 2.7, brackets
were required in field specifications.
See ovs-fields(7) for a list of fields and their names.
Port Specifications
Many Open vSwitch actions refer to OpenFlow ports. In such cases,
the port may be specified as a numeric port number in the range 0
to 65,535, although Open vSwitch only assigns port numbers in the
range 1 through 62,279 to ports. OpenFlow 1.1 and later use
32-bit port numbers, but Open vSwitch never assigns a port number
that requires more than 16 bits.
In most contexts, the name of a port may also be used. (The most
obvious context where a port name may not be used is in an
ovs-ofctl command along with the --no-names option.) When a
port’s name contains punctuation or could be ambiguous with other
actions, the name may be enclosed in double quotes, with JSON-like
string escapes supported (see [RFC 8259]).
Open vSwitch also supports the following standard OpenFlow port
names (even in contexts where port names are not otherwise
supported). The corresponding OpenFlow 1.0 and 1.1+ port numbers
are listed alongside them but should not be used in flow syntax:
• in_port (65528 or 0xfff8; 0xfffffff8)
• table (65529 or 0xfff9; 0xfffffff9)
• normal (65530 or 0xfffa; 0xfffffffa)
• flood (65531 or 0xfffb; 0xfffffffb)
• all (65532 or 0xfffc; 0xfffffffc)
• controller (65533 or 0xfffd; 0xfffffffd)
• local (65534 or 0xfffe; 0xfffffffe)
• any or none (65535 or 0xffff; 0xffffffff)
• unset (not in OpenFlow 1.0; 0xfffffff7)
These actions send a packet to a physical port or a controller. A
packet that never encounters an output action on its trip through
the Open vSwitch pipeline is effectively dropped. Because actions
are executed in order, a packet modification action that is not
eventually followed by an output action will not have an
externally visible effect.
The output action
Syntax:
port
output:port
output:field
output(port=port, max_len=nbytes)
Outputs the packet to an OpenFlow port most commonly specified as
port. Alternatively, the output port may be read from field, a
field or subfield in the syntax described under Field
Specifications above. Either way, if the port is the packet’s
input port, the packet is not output.
The port may be one of the following standard OpenFlow ports:
local Outputs the packet on the local port that corresponds to
the network device that has the same name as the bridge,
unless the packet was received on the local port.
OpenFlow switch implementations are not required to have
a local port, but Open vSwitch bridges always do.
in_port
Outputs the packet on the port on which it was received.
This is the only standard way to output the packet to
the input port (but see Output to the Input port,
below).
The port may also be one of the following additional OpenFlow
ports, unless max_len is specified:
normal Subjects the packet to the device’s normal L2/L3
processing. This action is not implemented by all
OpenFlow switches, and each switch implements it
differently. The section The OVS Normal Pipeline below
documents the OVS implementation.
flood Outputs the packet on all switch physical ports, except
the port on which it was received and any ports on which
flooding is disabled. Flooding can be disabled
automatically on a port by Open vSwitch when IEEE 802.1D
spanning tree (STP) or rapid spanning tree (RSTP) is
enabled, or by a controller using an OpenFlow
OFPT_MOD_PORT request to set the port’s OFPPC_NO_FLOOD
flag (ovs-ofctl mod-port provides a command-line
interface to set this flag).
all Outputs the packet on all switch physical ports except
the port on which it was received.
controller
Sends the packet and its metadata to an OpenFlow
controller or controllers encapsulated in an OpenFlow
packet-in message. The separate controller action,
described below, provides more options for output to a
controller.
Open vSwitch rejects output to other standard OpenFlow ports,
including none, unset, and port numbers reserved for future use as
standard ports, with the error OFPBAC_BAD_OUT_PORT.
With max_len, the packet is truncated to at most nbytes bytes
before being output. In this case, the output port may not be a
patch port. Truncation is just for the single output action, so
that later actions in the OpenFlow pipeline work with the complete
packet. The truncation feature is meant for use in monitoring
applications, e.g. for mirroring packets to a collector.
When an output action specifies the number of a port that does not
currently exist (and is not in the range for standard ports), the
OpenFlow specification allows but does not require OVS to reject
the action. All versions of Open vSwitch treat such an action as
a no-op. If a port with the number is created later, then the
action will be honored at that point. (OpenFlow requires OVS to
reject output to a port number that will never be valid, with
OFPBAC_BAD_OUT_PORT, but this situation does not arise when OVS is
a software switch, since the user can add or renumber ports at any
time.)
A controller can suppress output to a port by setting its
OFPPC_NO_FORWARD flag using an OpenFlow OFPT_MOD_PORT request
(ovs-ofctl mod-port provides a command-line interface to set this
flag). When output is disabled, output actions (and other actions
that output to the port) are allowed but have no effect.
Open vSwitch allows output to a port that does not exist, although
OpenFlow allows switches to reject such actions.
Conformance
All versions of OpenFlow and Open vSwitch support output to
a literal port. Output to a register is an OpenFlow
extension introduced in Open vSwitch 1.3. Output with
truncation is an OpenFlow extension introduced in Open
vSwitch 2.6.
Output to the Input Port
OpenFlow requires a switch to ignore attempts to send a packet out
its ingress port in the most straightforward way. For example,
output:234 has no effect if the packet has ingress port 234. The
rationale is that dropping these packets makes it harder to loop
the network. Sometimes this behavior can even be convenient, e.g.
it is often the desired behavior in a flow that forwards a packet
to several ports (floods the packet).
Sometimes one really needs to send a packet out its ingress port
(hairpin). In this case, use in_port to explicitly output the
packet to its input port, e.g.:
$ ovs-ofctl add-flow br0 in_port=2,actions=in_port
This also works in some circumstances where the flow doesn’t match
on the input port. For example, if you know that your switch has
five ports numbered 2 through 6, then the following will send
every received packet out every port, even its ingress port:
$ ovs-ofctl add-flow br0 actions=2,3,4,5,6,in_port
or, equivalently:
$ ovs-ofctl add-flow br0 actions=all,in_port
Sometimes, in complicated flow tables with multiple levels of
resubmit actions, a flow needs to output to a particular port that
may or may not be the ingress port. It’s difficult to take
advantage of output to in_port in this situation. To help, Open
vSwitch provides, as an OpenFlow extension, the ability to modify
the in_port field. Whatever value is currently in the in_port
field is both the port to which output will be dropped and the
destination for in_port. This means that the following adds flows
that reliably output to port 2 or to ports 2 through 6,
respectively:
$ ovs-ofctl add-flow br0 "in_port=2,actions=load:0->in_port,2"
$ ovs-ofctl add-flow br0 "actions=load:0->in_port,2,3,4,5,6"
If in_port is important for matching or other reasons, one may
save and restore it on the stack:
$ ovs-ofctl add-flow br0 \
actions="push:in_port,load:0->in_port,2,3,4,5,6,pop:in_port"
The OVS Normal Pipeline
This section documents how Open vSwitch implements output to the
normal port. The OpenFlow specification places no requirements on
how this port works, so all of this documentation is specific to
Open vSwitch.
Open vSwitch uses the Open_vSwitch database, detailed in
ovs-vswitchd.conf.db(5), to determine the details of the normal
pipeline.
The normal pipeline executes the following ingress stages for each
packet. Each stage either accepts the packet, in which case the
packet goes on to the next stage, or drops the packet, which
terminates the pipeline. The result of the ingress stages is a
set of output ports, which is the empty set if some ingress stage
drops the packet:
1. Input port lookup: Looks up the OpenFlow in_port field’s value
to the corresponding Port and Interface record in the
database.
The in_port is normally the OpenFlow port that the packet was
received on. If set_field or another actions changes the
in_port, the updated value is honored. Accept the packet if
the lookup succeeds, which it normally will. If the lookup
fails, for example because in_port was changed to an unknown
value, drop the packet.
2. Drop malformed packet: If the packet is malformed enough that
it contains only part of an 802.1Q header, then drop the
packet with an error.
3. Drop packets sent to a port reserved for mirroring: If the
packet was received on a port that is configured as the output
port for a mirror (that is, it is the output_port in some
Mirror record), then drop the packet.
4. VLAN input processing: This stage determines what VLAN the
packet is in. It also verifies that this VLAN is valid for
the port; if not, drop the packet. How the VLAN is determined
and which ones are valid vary based on the vlan-mode in the
input port’s Port record:
trunk The packet is in the VLAN specified in its 802.1Q
header, or in VLAN 0 if there is no 802.1Q header.
The trunks column in the Port record lists the valid
VLANs; if it is empty, all VLANs are valid.
access The packet is in the VLAN specified in the tag
column of its Port record. The packet must not have
an 802.1Q header with a nonzero VLAN ID; if it does,
drop the packet.
native-tagged / native-untagged
Same as trunk except that the VLAN of a packet
without an 802.1Q header is not necessarily zero;
instead, it is taken from the tag column.
dot1q-tunnel
The packet is in the VLAN specified in the tag
column of its Port record, which is a QinQ service
VLAN with the Ethertype specified by the Port’s
other_config:qinq-ethtype. If the packet has an
802.1Q header, then it specifies the customer VLAN.
The cvlans column specifies the valid customer
VLANs; if it is empty, all customer VLANs are valid.
5. Drop reserved multicast addresses: If the packet is addressed
to a reserved Ethernet multicast address and the Bridge record
does not have other_config:forward-bpdu set to true, drop the
packet.
6. LACP bond admissibility: This step applies only if the input
port is a member of a bond (a Port with more than one
Interface) and that bond is configured to use LACP. Otherwise,
skip to the next step.
The behavior here depends on the state of LACP negotiation:
• If LACP has been negotiated with the peer, accept the
packet if the bond member is enabled (i.e. carrier is up
and it hasn’t been administratively disabled).
Otherwise, drop the packet.
• If LACP negotiation is incomplete, then drop the packet.
There is one exception: if fallback to active-backup mode
is enabled, continue with the next step, pretending that
the active-backup balancing mode is in use.
7. Non-LACP bond admissibility: This step applies if the input
port is a member of a bond without LACP configured, or if a
LACP bond falls back to active-backup as described in the
previous step. If neither of these applies, skip to the next
step.
If the packet is an Ethernet multicast or broadcast, and not
received on the bond’s active member, drop the packet.
The remaining behavior depends on the bond’s balancing mode:
L4 (aka TCP balancing)
Drop the packet (this balancing mode is only
supported with LACP).
Active-backup
Accept the packet only if it was received on the
active member.
SLB (Source Load Balancing)
Drop the packet if the bridge has not learned the
packet’s source address (in its VLAN) on the port
that received it. Otherwise, accept the packet
unless it is a gratuitous ARP. Otherwise, accept
the packet if the MAC entry we found is ARP-locked.
Otherwise, drop the packet. (See the SLB Bonding
section in the OVS bonding document for more
information and a rationale.)
8. Learn source MAC: If the source Ethernet address is not a
multicast address, then insert a mapping from packet’s source
Ethernet address and VLAN to the input port in the bridge’s
MAC learning table. (This is skipped if the packet’s VLAN is
listed in the switch’s Bridge record in the flood_vlans
column, since there is no use for MAC learning when all
packets are flooded.)
When learning happens on a non-bond port, if the packet is a
gratuitous ARP, the entry is marked as ARP-locked. The lock
expires after 5 seconds. (See the SLB Bonding section in the
OVS bonding document for more information and a rationale.)
9. IP multicast path: If multicast snooping is enabled on the
bridge, and the packet is an Ethernet multicast but not an
Ethernet broadcast, and the packet is an IP packet, then the
packet takes a special processing path. This path is not yet
documented here.
10. Output port set: Search the MAC learning table for the port
corresponding to the packet’s Ethernet destination and VLAN.
If the search finds an entry, the output port set is just the
learned port. Otherwise (including the case where the packet
is an Ethernet multicast or in flood_vlans), the output port
set is all of the ports in the bridge that belong to the
packet’s VLAN, except for any ports that were disabled for
flooding via OpenFlow or that are configured in a Mirror
record as a mirror destination port.
The following egress stages execute once for each element in the
set of output ports. They execute (conceptually) in parallel, so
that a decision or action taken for a given output port has no
effect on those for another one:
1. Drop loopback: If the output port is the same as the input
port, drop the packet.
2. VLAN output processing: This stage adjusts the packet to
represent the VLAN in the correct way for the output port. Its
behavior varies based on the vlan-mode in the output port’s
Port record:
trunk / native-tagged / native-untagged
If the packet is in VLAN 0 (for native-untagged, if
the packet is in the native VLAN) drops any 802.1Q
header. Otherwise, ensures that there is an 802.1Q
header designating the VLAN.
access Remove any 802.1Q header that was present.
dot1q-tunnel
Ensures that the packet has an outer 802.1Q header
with the QinQ Ethertype and the specified configured
tag, and an inner 802.1Q header with the packet’s
VLAN.
3. VLAN priority tag processing: If VLAN output processing
discarded the 802.1Q headers, but priority tags are enabled
with other_config:priority-tags in the output port’s Port
record, then a priority-only tag is added (perhaps only if the
priority would be nonzero, depending on the configuration).
4. Bond member choice: If the output port is a bond, the code
chooses a particular member. This step is skipped for
non-bonded ports.
If the bond is configured to use LACP, but LACP negotiation is
incomplete, then normally the packet is dropped. The exception
is that if fallback to active-backup mode is enabled, the
egress pipeline continues choosing a bond member as if
active-backup mode was in use.
For active-backup mode, the output member is the active member.
Other modes hash appropriate header fields and use the hash
value to choose one of the enabled members.
5. Output: The pipeline sends the packet to the output port.
The controller action
Syntax:
controller
controller:max_len
controller(key[=value], ...)
Sends the packet and its metadata to an OpenFlow controller or
controllers encapsulated in an OpenFlow packet-in message. The
supported options are:
max_len=max_len
Limit to max_len the number of bytes of the packet to
send in the packet-in. A max_len of 0 prevents any of
the packet from being sent (thus, only metadata is
included). By default, the entire packet is sent,
equivalent to a max_len of 65535. This option has no
effect in Open vSwith 2.7 and later: the entire packet
will always be sent.
reason=reason
Specify reason as the reason for sending the message in
the packet-in. The supported reasons are no_match,
action, invalid_ttl, action_set, group, and packet_out.
The default reason is action.
id=controller_id
Specify controller_id, a 16-bit integer, as the
connection ID of the OpenFlow controller or controllers
to which the packet-in message should be sent. The
default is zero. Zero is also the default connection ID
for each controller connection, and a given controller
connection will only have a nonzero connection ID if its
controller uses the NXT_SET_CONTROLLER_ID Open vSwitch
extension to OpenFlow.
userdata=hh...
Supplies the bytes represented as hex digits hh as
additional data to the controller in the packet-in
message. Pairs of hex digits may be separated by
periods for readability.
pause Causes the switch to freeze the packet’s trip through
Open vSwitch flow tables and serializes that state into
the packet-in message as a continuation, an additional
property in the NXT_PACKET_IN2 message. The controller
can later send the continuation back to the switch in an
NXT_RESUME message, which will restart the packet’s
traversal from the point where it was interrupted. This
permits an OpenFlow controller to interpose on a packet
midway through processing in Open vSwitch.
Conformance
All versions of OpenFlow and Open vSwitch support
controller action and its max_len option. The userdata and
pause options require the Open vSwitch NXAST_CONTROLLER2
extension action added in Open vSwitch 2.6. In the absence
of these options, the reason (other than reason=action) and
controller_id (option than controller_id=0) options require
the Open vSwitch NXAST_CONTROLLER extension action added in
Open vSwitch 1.6.
Open vSwitch 2.7 and later is configured to not buffer
packets for the packet-in event. As a result, the full
packet is always sent to controllers. This means that the
max_len option has no effect on the controller action, and
all values (even 0) are equivalent to the default value of
65535.
The enqueue action
Syntax:
enqueue(port,queue)
enqueue:port:queue
Enqueues the packet on the specified queue within port port.
port must be an OpenFlow port number or name as described under
Port Specifications above. port may be in_port or local but the
other standard OpenFlow ports are not allowed.
queue must be a number between 0 and 4294967294 (0xfffffffe),
inclusive. The number of actually supported queues depends on the
switch. Some OpenFlow implementations do not support queuing at
all. In Open vSwitch, the supported queues vary depending on the
operating system, datapath, and hardware in use. Use the QoS and
Queue tables in the Open vSwitch database to configure queuing on
individual OpenFlow ports (see ovs-vswitchd.conf.db(5) for more
information).
Conformance
Only OpenFlow 1.0 supports enqueue. OpenFlow 1.1 added the
set_queue action to use in its place along with output.
Open vSwitch translates enqueue to a sequence of three
actions in OpenFlow 1.1 or later:
set_queue:queue,output:port,pop_queue. This is equivalent
in behavior as long as the flow table does not otherwise
use set_queue, but it relies on the pop_queue Open vSwitch
extension action.
The bundle and bundle_load actions
Syntax:
bundle(fields,basis,algorithm,ofport,members:port...)
bundle_load(fields,basis,algorithm,ofport,dst,members:port...)
These actions choose a port (a member) from a comma-separated
OpenFlow port list. After selecting the port, bundle outputs to
it, whereas bundle_load writes its port number to dst, which must
be a 16-bit or wider field or subfield in the syntax described
under Field Specifications above.
These actions hash a set of fields using basis as a universal hash
parameter, then apply the bundle link selection algorithm to
choose a port.
fields must be one of the following. For the options with
symmetric in the name, reversing source and destination addresses
yields the same hash:
eth_src
Ethernet source address.
nw_src IPv4 or IPv6 source address.
nw_dst IPv4 or IPv6 destination address.
symmetric_l4
Ethernet source and destination, Ethernet type, VLAN ID
or IDs (if any), IPv4 or IPv6 source and destination, IP
protocol, TCP or SCTP (but not UDP) source and
destination.
symmetric_l3l4
IPv4 or IPv6 source and destination, IP protocol, TCP or
SCTP (but not UDP) source and destination.
symmetric_l3l4+udp
Like symmetric_l3l4 but include UDP ports.
algorithm must be one of the following:
active_backup
Chooses the first live port listed in members.
hrw (Highest Random Weight)
Computes the following, considering only the live ports
in members:
for i in [1, n_members]:
weights[i] = hash(flow, i)
member = { i such that weights[i] >= weights[j] for all j != i }
This algorithm is specified by RFC 2992.
The algorithms take port liveness into account when selecting
members. The definition of whether a port is live is subject to
change. It currently takes into account carrier status and link
monitoring protocols such as BFD and CFM. If none of the members
is live, bundle does not output the packet and bundle_load stores
OFPP_NONE (65535) in the output field.
Example: bundle(eth_src,0,hrw,ofport,members:4,8) uses an Ethernet
source hash with basis 0, to select between OpenFlow ports 4 and 8
using the Highest Random Weight algorithm.
Conformance
Open vSwitch 1.2 introduced the bundle and bundle_load
OpenFlow extension actions.
The group action
Syntax:
group:group
Outputs the packet to the OpenFlow group group, which must be a
number in the range 0 to 4294967040 (0xffffff00). The group must
exist or Open vSwitch will refuse to add the flow. When a group
is deleted, Open vSwitch also deletes all of the flows that output
to it.
Groups contain action sets, whose semantics are described above in
the section Action Sets. The semantics of action sets can be
surprising to users who expect action list semantics, since action
sets reorder and sometimes ignore actions.
A group action usually executes the action set or sets in one or
more group buckets. Open vSwitch saves the packet and metadata
before it executes each bucket, and then restores it afterward.
Thus, when a group executes more than one bucket, this means that
each bucket executes on the same packet and metadata. Moreover,
regardless of the number of buckets executed, the packet and
metadata are the same before and after executing the group.
Sometimes saving and restoring the packet and metadata can be
undesirable. In these situations, workarounds are possible. For
example, consider a pipeline design in which a select group bucket
is to communicate to a later stage of processing a value based on
which bucket was selected. An obvious design would be for the
bucket to communicate the value via set_field on a register. This
does not work because registers are part of the metadata that
group saves and restores. The following alternative bucket
designs do work:
• Recursively invoke the rest of the pipeline with resubmit.
• Use resubmit into a table that uses push to put the value on
the stack for the caller to pop off. This works because
group preserves only packet data and metadata, not the stack.
(This design requires indirection through resubmit because
actions sets may not contain push or pop actions.)
An exit action within a group bucket terminates only execution of
that bucket, not other buckets or the overall pipeline.
Conformance
OpenFlow 1.1 introduced group. Open vSwitch 2.6 and later
also supports group as an extension to OpenFlow 1.0.
The strip_vlan and pop actions
Syntax:
strip_vlan
pop_vlan
Removes the outermost VLAN tag, if any, from the packet.
The two names for this action are synonyms with no semantic
difference. The OpenFlow 1.0 specification uses the name
strip_vlan and later versions use pop_vlan, but OVS accepts either
name regardless of version.
In OpenFlow 1.1 and later, consistency rules allow strip_vlan only
in a flow that matches only packets with a VLAN tag (or following
an action that pushes a VLAN tag, such as push_vlan). See
Inconsistencies, above, for more information.
Conformance
All versions of OpenFlow and Open vSwitch support this
action.
The push_vlan action
Syntax:
push_vlan:ethertype
Pushes a new outermost VLAN onto the packet. Uses TPID ethertype,
which must be 0x8100 for an 802.1Q C-tag or 0x88a8 for a 802.1ad
S-tag.
Conformance
OpenFlow 1.1 and later supports this action. Open vSwitch
2.8 added support for multiple VLAN tags (with a limit of
2) and 802.1ad S-tags.
The push_mpls action
Syntax:
push_mpls:ethertype
Pushes a new outermost MPLS label stack entry (LSE) onto the
packet and changes the packet’s Ethertype to ethertype, which must
be either B0x8847 or 0x8848. If the packet did not already
contain any MPLS labels, initializes the new LSE as:
Label 2, if the packet contains IPv6, 0 otherwise.
TC The low 3 bits of the packet’s DSCP value, or 0 if the
packet is not IP.
TTL Copied from the IP TTL, or 64 if the packet is not IP.
If the packet did already contain an MPLS label, initializes the
new outermost label as a copy of the existing outermost label.
OVS currently supports at most 3 MPLS labels.
This action applies only to Ethernet packets.
Conformance
Open vSwitch 1.11 introduced support for MPLS. OpenFlow
1.1 and later support push_mpls. Open vSwitch implements
push_mpls as an extension to OpenFlow 1.0.
The pop_mpls action
Syntax:
pop_mpls:ethertype
Strips the outermost MPLS label stack entry and changes the
packet’s Ethertype to ethertype. This action applies only to
Ethernet packets with at least one MPLS label. If there is more
than one MPLS label, then ethertype should be an MPLS Ethertype
(B0x8847 or 0x8848).
Conformance
Open vSwitch 1.11 introduced support for MPLS. OpenFlow
1.1 and later support pop_mpls. Open vSwitch implements
pop_mpls as an extension to OpenFlow 1.0.
The encap action
Syntax:
encap(nsh([md_type=md_type], [tlv(class,type,value)]...))
encap(ethernet)
encap(mpls)
encap(mpls_mc)
The encap action encapsulates a packet with a specified header.
It has variants for different kinds of encapsulation.
The encap(nsh(...)) variant encapsulates an Ethernet frame with
NSH. The md_type may be 1 or 2 for metadata type 1 or 2,
defaulting to 1. For metadata type 2, TLVs may be specified with
class as a 16-bit hexadecimal integer beginning with 0x, type as
an 8-bit decimal integer, and value a sequence of pairs of hex
digits beginning with 0x. For example:
encap(nsh(md_type=1))
Encapsulates the packet with an NSH header with metadata
type 1.
encap(nsh(md_type=2,tlv(0x1000,10,0x12345678)))
Encapsulates the packet with an NSH header, NSH metadata
type 2, and an NSH TLV with class 0x1000, type 10, and
the 4-byte value 0x12345678.
The encap(ethernet) variant encapsulate a bare L3 packet in an
Ethernet frame. The Ethernet type is initialized to the L3
packet’s type, e.g. 0x0800 if the L3 packet is IPv4. The Ethernet
source and destination are initially zeroed.
The encap(mpls) variant adds a MPLS header at the start of the
packet. When encap(ethernet) is applied after this action, the
ethertype of ethernet header will be populated with MPLS unicast
ethertype (0x8847).
The encap(mpls_mc) variant adds a MPLS header at the start of the
packet. When encap(ethernet) is applied after this action, the
ethertype of ethernet header will be populated with MPLS multicast
ethertype (0x8848).
Conformance
This action is an Open vSwitch extension to OpenFlow 1.3
and later, introduced in Open vSwitch 2.8.
The MPLS support for this action is added in Open vSwitch
2.17.
The decap action
Syntax:
decap
decap(packet_type(ns=namespace,type=type))
Removes an outermost encapsulation from the packet:
• If the packet is an Ethernet packet, removes the Ethernet
header, which changes the packet into a bare L3 packet. If
the packet has VLAN tags, raises an unsupported packet type
error (see Error Handling, above).
• Otherwise, if the packet is an NSH packet, removes the NSH
header, revealing the inner packet. Open vSwitch supports
Ethernet, IPv4, IPv6, and NSH inner packet types. Other
types raise unsupported packet type errors.
• Otherwise, if the packet is encapsulated inside a MPLS
header, removes the MPLS header and classifies the inner
packet as mentioned in the packet type argument of the decap.
The packet_type field specifies the type of the packet in the
format specified in OpenFlow 1.5 chapter 7.2.3.11 Packet Type
Match Field. The inner packet will be incorrectly
classified, if the inner packet is different from mentioned
in the packet_type field.
• Otherwise, raises an unsupported packet type error.
Conformance
This action is an Open vSwitch extension to OpenFlow 1.3
and later, introduced in Open vSwitch 2.8.
The MPLS support for this action is added in Open vSwitch
2.17.
These actions modify packet data and metadata fields.
The set_field and load actions
Syntax:
set_field:value[/mask]->dst
load:value->dst
These actions loads a literal value into a field or part of a
field. The set_field action takes value in the customary syntax
for field dst, e.g. 00:11:22:33:44:55 for an Ethernet address, and
dst as the field’s name. The optional mask allows part of a field
to be set.
The load action takes value as an integer value (in decimal or
prefixed by 0x for hexadecimal) and dst as a field or subfield in
the syntax described under Field Specifications above.
The following all set the Ethernet source address to
00:11:22:33:44:55:
• set_field:00:11:22:33:44:55->eth_src
• load:0x001122334455->eth_src
• load:0x001122334455->OXM_OF_ETH_SRC[]
The following all set the multicast bit in the Ethernet
destination address:
• set_field:01:00:00:00:00:00/01:00:00:00:00:00->eth_dst
• load:1->eth_dst[40]
Open vSwitch prohibits a set_field or load action whose dst is not
guaranteed to be part of the packet; for example, set_field of
nw_dst is only allowed in a flow that matches on Ethernet type
0x800. In some cases, such as in an action set, Open vSwitch
can’t statically check that dst is part of the packet, and in that
case if it is not then Open vSwitch treats the action as a no-op.
Conformance
Open vSwitch 1.1 introduced NXAST_REG_LOAD as a extension
to OpenFlow 1.0 and used load to express it. Later,
OpenFlow 1.2 introduced a standard OFPAT_SET_FIELD action
that was restricted to loading entire fields, so Open
vSwitch added the form set_field with this restriction.
OpenFlow 1.5 extended OFPAT_SET_FIELD to the point that it
became a superset of NXAST_REG_LOAD. Open vSwitch
translates either syntax as necessary for the OpenFlow
version in use: in OpenFlow 1.0 and 1.1, NXAST_REG_LOAD; in
OpenFlow 1.2, 1.3, and 1.4, NXAST_REG_LOAD for load or for
loading a subfield, OFPAT_SET_FIELD otherwise; and OpenFlow
1.5 and later, OFPAT_SET_FIELD.
The move action
Syntax:
move:src->dst
Copies the named bits from field or subfield src to field or
subfield dst. src and dst should fields or subfields in the
syntax described under Field Specifications above. The two fields
or subfields must have the same width.
Examples:
• move:reg0[0..5]->reg1[26..31] copies the six bits numbered 0
through 5 in register 0 into bits 26 through 31 of register
1.
• move:reg0[0..15]->vlan_tci copies the least significant 16
bits of register 0 into the VLAN TCI field.
Conformance
In OpenFlow 1.0 through 1.4, move ordinarily uses an Open
vSwitch extension to OpenFlow. In OpenFlow 1.5, move uses
the OpenFlow 1.5 standard OFPAT_COPY_FIELD action. The ONF
has also made OFPAT_COPY_FIELD available as an extension to
OpenFlow 1.3. Open vSwitch 2.4 and later understands this
extension and uses it if a controller uses it, but for
backward compatibility with older versions of Open vSwitch,
ovs-ofctl does not use it.
The mod_dl_src and mod_dl_dst actions
Syntax:
mod_dl_src:mac
mod_dl_dst:mac
Sets the Ethernet source or destination address, respectively, to
mac, which should be expressed in the form xx:xx:xx:xx:xx:xx.
For L3-only packets, that is, those that lack an Ethernet header,
this action has no effect.
Conformance
OpenFlow 1.0 and 1.1 have specialized actions for these
purposes. OpenFlow 1.2 and later do not, so Open vSwitch
translates them to appropriate OFPAT_SET_FIELD actions for
those versions,
The mod_nw_src and mod_nw_dst actions
Syntax:
mod_nw_src:ip
mod_nw_dst:ip
Sets the IPv4 source or destination address, respectively, to ip,
which should be expressed in the form w.x.y.z.
In OpenFlow 1.1 and later, consistency rules allow these actions
only in a flow that matches only packets that contain an IPv4
header (or following an action that adds an IPv4 header, e.g.
pop_mpls:0x0800). See Inconsistencies, above, for more
information.
Conformance
OpenFlow 1.0 and 1.1 have specialized actions for these
purposes. OpenFlow 1.2 and later do not, so Open vSwitch
translates them to appropriate OFPAT_SET_FIELD actions for
those versions,
The mod_nw_tos and mod_nw_ecn actions
Syntax:
mod_nw_tos:tos
mod_nw_ecn:ecn
The mod_nw_tos action sets the DSCP bits in the IPv4 ToS/DSCP or
IPv6 traffic class field to tos, which must be a multiple of 4
between 0 and 255. This action does not modify the two least
significant bits of the ToS field (the ECN bits).
The mod_nw_ecn action sets the ECN bits in the IPv4 ToS or IPv6
traffic class field to ecn, which must be a value between 0 and 3,
inclusive. This action does not modify the six most significant
bits of the field (the DSCP bits).
In OpenFlow 1.1 and later, consistency rules allow these actions
only in a flow that matches only packets that contain an IPv4 or
IPv6 header (or following an action that adds such a header). See
Inconsistencies, above, for more information.
Conformance
OpenFlow 1.0 has a mod_nw_tos action but not mod_nw_ecn.
Open vSwitch implements the latter in OpenFlow 1.0 as an
extension using NXAST_REG_LOAD. OpenFlow 1.1 has
specialized actions for these purposes. OpenFlow 1.2 and
later do not, so Open vSwitch translates them to
appropriate OFPAT_SET_FIELD actions for those versions.
The mod_tp_src and mod_tp_dst actions
Syntax:
mod_tp_src:port
mod_tp_dst:port
Sets the TCP or UDP or SCTP source or destination port,
respectively, to port. Both IPv4 and IPv6 are supported.
In OpenFlow 1.1 and later, consistency rules allow these actions
only in a flow that matches only packets that contain a TCP or UDP
or SCTP header. See Inconsistencies, above, for more information.
Conformance
OpenFlow 1.0 and 1.1 have specialized actions for these
purposes. OpenFlow 1.2 and later do not, so Open vSwitch
translates them to appropriate OFPAT_SET_FIELD actions for
those versions,
The dec_ttl action
Syntax:
dec_ttl
dec_ttl(id1[,id2[, ...]])
Decrement TTL of IPv4 packet or hop limit of IPv6 packet. If the
TTL or hop limit is initially 0 or 1, no decrement occurs, as
packets reaching TTL zero must be rejected. Instead, Open vSwitch
sends a packet-in message with reason code OFPR_INVALID_TTL to
each connected controller that has enabled receiving such
messages, and stops processing the current set of actions.
(However, if the current set of actions was reached through
resubmit, the remaining actions in outer levels resume
processing.)
As an Open vSwitch extension to OpenFlow, this action supports the
ability to specify a list of controller IDs. Open vSwitch will
only send the message to controllers with the given ID or IDs.
Specifying no list is equivalent to specifying a single controller
ID of zero.
In OpenFlow 1.1 and later, consistency rules allow these actions
only in a flow that matches only packets that contain an IPv4 or
IPv6 header. See Inconsistencies, above, for more information.
Conformance
All versions of OpenFlow and Open vSwitch support this
action.
The set_mpls_label, set_mpls_tc, and set_mpls_ttl actions
Syntax:
set_mpls_label:label
set_mpls_tc:tc
set_mpls_ttl:ttl
The set_mpls_label action sets the label of the packet’s outer
MPLS label stack entry. label should be a 20-bit value that is
decimal by default; use a 0x prefix to specify the value in
hexadecimal.
The set_mpls_tc action sets the traffic class of the packet’s
outer MPLS label stack entry. tc should be in the range 0 to 7,
inclusive.
The set_mpls_ttl action sets the TTL of the packet’s outer MPLS
label stack entry. ttl should be in the range 0 to 255 inclusive.
In OpenFlow 1.1 and later, consistency rules allow these actions
only in a flow that matches only packets that contain an MPLS
label (or following an action that adds an MPLS label, e.g.
push_mpls:0x8847). See Inconsistencies, above, for more
information.
Conformance
OpenFlow 1.0 does not support MPLS, but Open vSwitch
implements these actions as extensions. OpenFlow 1.1 has
specialized actions for these purposes. OpenFlow 1.2 and
later do not, so Open vSwitch translates them to
appropriate OFPAT_SET_FIELD actions for those versions,
The dec_mpls_ttl and dec_nsh_ttl actions
Syntax:
dec_mpls_ttl
dec_nsh_ttl
These actions decrement the TTL of the packet’s outer MPLS label
stack entry or its NSH header, respectively. If the TTL is
initially 0 or 1, no decrement occurs. Instead, Open vSwitch
sends a packet-in message with reason code BOFPR_INVALID_TTL to
OpenFlow controllers with ID 0, if it has enabled receiving them.
Processing the current set of actions then stops. (However, if
the current set of actions was reached through resubmit, remaining
actions in outer levels resume processing.)
In OpenFlow 1.1 and later, consistency rules allow this actions
only in a flow that matches only packets that contain an MPLS
label or an NSH header, respectively. See Inconsistencies, above,
for more information.
Conformance
Open vSwitch 1.11 introduced support for MPLS. OpenFlow
1.1 and later support dec_mpls_ttl. Open vSwitch
implements dec_mpls_ttl as an extension to OpenFlow 1.0.
Open vSwitch 2.8 introduced support for NSH, although the
NSH draft changed after release so that only Open vSwitch
2.9 and later conform to the final protocol specification.
The dec_nsh_ttl action and NSH support in general is an
Open vSwitch extension not supported by any version of
OpenFlow.
The check_pkt_larger action
Syntax:
check_pkt_larger(pkt_len)->dst
Checks if the packet is larger than the specified length in
pkt_len. If so, stores 1 in dst, which should be a 1-bit field;
if not, stores 0.
The packet length to check against the argument pkt_len includes
the L2 header and L2 payload of the packet, but not the VLAN tag
(if present).
Examples:
• check_pkt_larger(1500)->reg0[0]
• check_pkt_larger(8000)->reg9[10]
This action was added in Open vSwitch 2.12.
The delete_field action
Syntax:
delete_field:field
The delete_field action deletes a field in the syntax described
under Field Specifications above. Currently, only the
tun_metadata fields are supported.
This action was added in Open vSwitch 2.14.
The set_tunnel action
Syntax:
set_tunnel:id
set_tunnel64:id
Many kinds of tunnels support a tunnel ID, e.g. VXLAN and Geneve
have a 24-bit VNI, and GRE has an optional 32-bit key. This
action sets the value used for tunnel ID in such tunneled packets,
although whether it is used for a particular tunnel depends on the
tunnel’s configuration. See the tunnel ID documentation in
ovs-fields(7) for more information.
Conformance
These actions are OpenFlow extensions. set_tunnel was
introduced in Open vSwitch 1.0. set_tunnel64, which is
needed if id is wider than 32 bits, was added in Open
vSwitch 1.1. Both actions always set the entire tunnel ID
field. Open vSwitch supports these actions in all versions
of OpenFlow, but in OpenFlow 1.2 and later it translates
them to an appropriate standardized OFPAT_SET_FIELD action.
The set_queue and pop_queue actions
Syntax:
set_queue:queue
pop_queue
The set_queue action sets the queue ID to be used for subsequent
output actions to queue, which must be a 32-bit integer. The
range of meaningful values of queue, and their meanings, varies
greatly from one OpenFlow implementation to another. Even within
a single implementation, there is no guarantee that all OpenFlow
ports have the same queues configured or that all OpenFlow ports
in an implementation can be configured the same way queue-wise.
For more information, see the documentation for the output queue
field in ovs-fields(7).
The pop_queue restores the output queue to the default that was
set when the packet entered the switch (generally 0).
Four billion queues ought to be enough for anyone: ]8;;https://mailman.stanford.edu/pipermail/openflow-spec/2009-August/000394.html\‐
https://mailman.stanford.edu/pipermail/openflow-spec/2009-August/000394.html ]8;;\
Conformance
OpenFlow 1.1 introduced the set_queue action. Open vSwitch
also supports it as an extension in OpenFlow 1.0.
The pop_queue action is an Open vSwitch extension.
Open vSwitch is often used to implement a firewall. The preferred
way to implement a firewall is connection tracking, that is, to
keep track of the connection state of individual TCP sessions.
The ct action described in this section, added in Open vSwitch
2.5, implements connection tracking. For new deployments, it is
the recommended way to implement firewalling with Open vSwitch.
Before ct was added, Open vSwitch did not have built-in support
for connection tracking. Instead, Open vSwitch supported the
learn action, which allows a received packet to add a flow to an
OpenFlow flow table. This could be used to implement a primitive
form of connection tracking: packets passing through the firewall
in one direction could create flows that allowed response packets
back through the firewall in the other direction. The additional
fin_timeout action allowed the learned flows to expire quickly
after TCP session termination.
The ct action
Syntax:
ct([argument]...)
ct(commit[,argument]...)
The action has two modes of operation, distinguished by whether
commit is present. The following arguments may be present in
either mode:
zone=value
A zone is a 16-bit id that isolates connections into
separate domains, allowing overlapping network addresses
in different zones. If a zone is not provided, then the
default is 0. The value may be specified either as a
16-bit integer literal or a field or subfield in the
syntax described under Field Specifications above.
Without commit, this action sends the packet through the
connection tracker. The connection tracker keeps track of the
state of TCP connections for packets passed through it. For each
packet through a connection, it checks that it satisfies TCP
invariants and signals the connection state to later actions using
the ct_state metadata field, which is documented in ovs-fields(7).
In this form, ct forks the OpenFlow pipeline:
• In one fork, ct passes the packet to the connection tracker.
Afterward, it reinjects the packet into the OpenFlow pipeline
with the connection tracking fields initialized. The
ct_state field is initialized with connection state and
ct_zone to the connection tracking zone specified on the zone
argument. If the connection is one that is already tracked,
ct_mark and ct_label to its existing mark and label,
respectively; otherwise they are zeroed. In addition,
ct_nw_proto, ct_nw_src, ct_nw_dst, ct_ipv6_src, ct_ipv6_dst,
ct_tp_src, and ct_tp_dst are initialized appropriately for
the original direction connection. See the resubmit action
for a way to search the flow table with the connection
tracking original direction fields swapped with the packet
5-tuple fields. See ovs-fields(7) for details on the
connection tracking fields.
• In the other fork, the original instance of the packet
continues independent processing following the ct action.
The ct_state field and other connection tracking metadata are
cleared.
Without commit, the ct action accepts the following arguments:
table=table
Sets the OpenFlow table where the packet is reinjected.
The table must be a number between 0 and 254 inclusive,
or a table’s name. If table is not specified, then the
packet is not reinjected.
nat
nat(type=addrs[:ports][,flag]...)
Specify address and port translation for the connection
being tracked. The type must be src, for source
address/port translation (SNAT), or dst, for destination
address/port translation (DNAT). Setting up address
translation for a new connection takes effect only if
the connection is later committed with ct(commit ...).
The src and dst options take the following arguments:
addrs The IP address addr or range addr1-addr2 from
which the translated address should be
selected. If only one address is given, then
that address will always be selected,
otherwise the address selection can be
informed by the optional persistent flag as
described below. Either IPv4 or IPv6
addresses can be provided, but both addresses
must be of the same type, and the datapath
behavior is undefined in case of providing
IPv4 address range for an IPv6 packet, or
IPv6 address range for an IPv4 packet. IPv6
addresses must be bracketed with [ and ] if a
port range is also given.
ports The L4 port or range port1-port2 from which
the translated port should be selected. When
a port range is specified, fallback to
ephemeral ports does not happen, else, it
will. The port number selection can be
informed by the optional random and hash
flags described below.
The optional flags are:
random The selection of the port from the given
range should be done using a fresh random
number. This flag is mutually exclusive with
hash.
hash The selection of the port from the given
range should be done using a datapath
specific hash of the packet’s IP addresses
and the other, non-mapped port number. This
flag is mutually exclusive with random.
persistent
The selection of the IP address from the
given range should be done so that the same
mapping can be provided after the system
restarts.
If alg is specified for the committing ct action that
also includes nat with a src or dst attribute, then the
datapath tries to set up the helper to be NAT-aware.
This functionality is datapath specific and may not be
supported by all datapaths.
A bare nat argument with no options will only translate
the packet being processed in the way the connection has
been set up with an earlier, committed ct action. A nat
action with src or dst, when applied to a packet
belonging to an established (rather than new)
connection, will behave the same as a bare nat.
For SNAT, there is a special case when the src IP
address is configured as all 0’s, i.e.,
nat(src=0.0.0.0). In this case, when a source port
collision is detected during the commit, the source port
will be translated to an ephemeral port. If there is no
collision, no SNAT is performed.
Open vSwitch 2.6 introduced nat. Linux 4.6 was the
earliest upstream kernel that implemented ct support for
nat.
With commit, the connection tracker commits the connection to the
connection tracking module. The commit flag should only be used
from the pipeline within the first fork of ct without commit.
Information about the connection is stored beyond the lifetime of
the packet in the pipeline. Some ct_state flags are only
available for committed connections.
The following options are available only with commit:
force A committed connection always has the directionality of
the packet that caused the connection to be committed in
the first place. This is the original direction of the
connection, and the opposite direction is the reply
direction. If a connection is already committed, but it
is in the wrong direction, force effectively terminates
the existing connection and starts a new one in the
current direction. This flag has no effect if the
original direction of the connection is already the same
as that of the current packet.
exec(action...)
Perform each action within the context of connection
tracking. Only actions which modify the ct_mark or
ct_label fields are accepted within exec action, and
these fields may only be modified with this option. For
example:
set_field:value[/mask]->ct_mark
Store a 32-bit metadata value with the
connection. Subsequent lookups for packets in
this connection will populate ct_mark when the
packet is sent to the connection tracker with the
table specified.
set_field:value[/mask]->ct_label
Store a 128-bit metadata value with the
connection. Subsequent lookups for packets in
this connection will populate ct_label when the
packet is sent to the connection tracker with the
table specified.
alg=alg
Specify application layer gateway alg to track specific
connection types. If subsequent related connections are
sent through the ct action, then the rel flag in the
ct_state field will be set. Supported types include:
ftp Look for negotiation of FTP data connections.
Specify this option for FTP control connections
to detect related data connections and populate
the rel flag for the data connections.
tftp Look for negotiation of TFTP data connections.
Specify this option for TFTP control connections
to detect related data connections and populate
the rel flag for the data connections.
Related connections inherit ct_mark from that stored
with the original connection (i.e. the connection
created by ct(alg=...).
With the Linux datapath, global sysctl options affect ct behavior.
In particular, if net.netfilter.nf_conntrack_helper is enabled,
which it is by default until Linux 4.7, then application layer
gateway helpers may be executed even if alg is not specified. For
security reasons, the netfilter team recommends users disable this
option. For further details, please see ]8;;http://www.netfilter.org/news.html#2012-04-03\‐
http://www.netfilter.org/news.html#2012-04-03 ]8;;\ .
The ct action may be used as a primitive to construct stateful
firewalls by selectively committing some traffic, then matching
ct_state to allow established connections while denying new
connections. The following flows provide an example of how to
implement a simple firewall that allows new connections from port
1 to port 2, and only allows established connections to send
traffic from port 2 to port 1:
table=0,priority=1,action=drop
table=0,priority=10,arp,action=normal
table=0,priority=100,ip,ct_state=-trk,action=ct(table=1)
table=1,in_port=1,ip,ct_state=+trk+new,action=ct(commit),2
table=1,in_port=1,ip,ct_state=+trk+est,action=2
table=1,in_port=2,ip,ct_state=+trk+new,action=drop
table=1,in_port=2,ip,ct_state=+trk+est,action=1
If ct is executed on IPv4 (or IPv6) fragments, then the message is
implicitly reassembled before sending to the connection tracker
and refragmented upon output, to the original maximum received
fragment size. Reassembly occurs within the context of the zone,
meaning that IP fragments in different zones are not assembled
together. Pipeline processing for the initial fragments is
halted. When the final fragment is received, the message is
assembled and pipeline processing continues for that flow. Packet
ordering is not guaranteed by IP protocols, so it is not possible
to determine which IP fragment will cause message reassembly (and
therefore continue pipeline processing). As such, it is strongly
recommended that multiple flows should not execute ct to
reassemble fragments from the same IP message.
Conformance
The ct action was introduced in Open vSwitch 2.5. Some of
its features were introduced later, noted individually
above.
The ct_clear action
Syntax:
ct_clear
Clears connection tracking state from the flow, zeroing ct_state,
ct_zone, ct_mark, and ct_label.
This action was introduced in Open vSwitch 2.7.
The learn action
Syntax:
learn(argument...)
The learn action adds or modifies a flow in an OpenFlow table,
similar to ovs-ofctl --strict mod-flows. The arguments specify
the match fields, actions, and other properties of the flow to be
added or modified.
Match fields for the new flow are specified as follows. At least
one match field should ordinarily be specified:
field=value
Specifies that field, in the new flow, must match the
literal value, e.g. dl_type=0x800. Shorthand match
syntax, such as ip in place of dl_type=0x800, is not
supported.
field=src
Specifies that field in the new flow must match src
taken from the packet currently being processed. For
example, udp_dst=udp_src, applied to a UDP packet with
source port 53, creates a flow which matches udp_dst=53.
field and src must have the same width.
field Shorthand for the previous form when field and src are
the same. For example, udp_dst, applied to a UDP packet
with destination port 53, creates a flow which matches
udp_dst=53.
The field and src arguments above should be fields or subfields in
the syntax described under Field Specifications above.
Match field specifications must honor prerequisites for both the
flow with the learn and the new flow that it creates. Consider
the following complete flow, in the syntax accepted by ovs-ofctl.
If the flow’s match on udp were omitted, then the flow would not
satisfy the prerequisites for the learn action’s use of udp_src.
If dl_type=0x800 or nw_proto were omitted from learn, then the new
flow would not satisfy the prerequisite for its match on udp_dst.
For more information on prerequisites, please refer to
ovs-fields(7):
udp, actions=learn(dl_type=0x800, nw_proto=17, udp_dst=udp_src)
Actions for the new flow are specified as follows. At least one
action should ordinarily be specified:
load:value->dst
Adds a load action to the new flow that loads the
literal value into dst. The syntax is the same as the
load action explained in the Field Modification Actions
section.
load:src->dst
Adds a load action to the new flow that loads src, a
field or subfield from the packet being processed, into
dst.
output:field
Adds an output action to the new flow’s actions that
outputs to the OpenFlow port taken from field, which
must be a field as described above.
fin_idle_timeout=seconds / fin_hard_timeout=seconds
Adds a fin_timeout action with the specified arguments
to the new flow. This feature was added in Open vSwitch
1.6.
The following additional arguments are optional:
idle_timeout=seconds
hard_timeout=seconds
priority=value
cookie=value
send_flow_rem
These arguments have the same meaning as in the usual
flow syntax documented in ovs-ofctl(8).
table=table
The table in which the new flow should be inserted.
Specify a decimal number between 0 and 254 inclusive or
the name of a table. The default, if table is
unspecified, is table 1 (not 0).
delete_learned
When this flag is specified, deleting the flow that
contains the learn action will also delete the flows
created by learn. Specifically, when the last learn
action with this flag and particular table and cookie
values is removed, the switch deletes all of the flows
in the specified table with the specified cookie.
This flag was added in Open vSwitch 2.4.
limit=number
If the number of flows in the new flow’s table with the
same cookie exceeds number, the action will not add a
new flow. By default, or with limit=0, there is no
limit.
This flag was added in Open vSwitch 2.8.
result_dst=field[bit]
If learn fails (because the number of flows exceeds
limit), the action sets field[bit] to 0, otherwise it
will be set to 1. field[bit] must be a single bit.
This flag was added in Open vSwitch 2.8.
By itself, the learn action can only put two kinds of actions into
the flows that it creates: load and output actions. If learn is
used in isolation, these are severe limits.
However, learn is not meant to be used in isolation. It is a
primitive meant to be used together with other Open vSwitch
features to accomplish a task. Its existing features are enough
to accomplish most tasks.
Here is an outline of a typical pipeline structure that allows for
versatile behavior using learn:
• Flows in table A contain a learn action, that populates flows
in table L, that use a load action to populate register R
with information about what was learned.
• Flows in table B contain two sequential resubmit actions: one
to table L and another one to table B + 1.
• Flows in table B + 1 match on register R and act differently
depending on what the flows in table L loaded into it.
This approach can be used to implement many learn-based features.
For example:
• Resubmit to a table selected based on learned information,
e.g. see ]8;;https://mail.openvswitch.org/pipermail/ovs-discuss/2016-June/021694.html\‐
https://mail.openvswitch.org/pipermail/ovs-discuss/2016-June/021694.html ]8;;\
.
• MAC learning in the middle of a pipeline, as described in the
Open vSwitch Advanced Features Tutorial in the OVS
documentation.
• TCP state based firewalling, by learning outgoing connections
based on SYN packets and matching them up with incoming
packets. (This is usually better implemented using the ct
action.)
• At least some of the features described in T. A. Hoff,
Extending Open vSwitch to Facilitate Creation of Stateful SDN
Applications.
Conformance
The learn action is an Open vSwitch extension to OpenFlow
added in Open vSwitch 1.3. Some features of learn were
added in later versions, as noted individually above.
The fin_timeout action
Syntax:
fin_timeout(key=value...)
This action changes the idle timeout or hard timeout, or both, of
the OpenFlow flow that contains it, when the flow matches a TCP
packet with the FIN or RST flag. When such a packet is observed,
the action reduces the rule’s timeouts to those specified on the
action. If the rule’s existing timeout is already shorter than
the one that the action specifies, then that timeout is
unaffected.
The timeouts are specified as key-value pairs:
idle_timeout=seconds
Causes the flow to expire after the given number of
seconds of inactivity.
hard_timeout=seconds
Causes the flow to expire after the given number of
seconds, regardless of activity. (seconds specifies
time since the flow’s creation, not since the receipt of
the FIN or RST.)
This action is normally added to a learned flow by the learn
action. It is unlikely to be useful otherwise.
Conformance
This Open vSwitch extension action was added in Open
vSwitch 1.6.
The resubmit action
Syntax:
resubmit:port
resubmit([port],[table][,ct])``
Searches an OpenFlow flow table for a matching flow and executes
the actions found, if any, before continuing to the following
action in the current flow entry. Arguments can customize the
search:
• If port is given as an OpenFlow port number or name, then it
specifies a value to use for the input port metadata field as
part of the search, in place of the input port currently in
the flow. Specifying in_port as port is equivalent to
omitting it.
• If table is given as an integer between 0 and 254 or a table
name, it specifies the OpenFlow table to search. If it is
not specified, the table from the current flow is used.
• If ct is specified, then the search is done with packet
5-tuple fields swapped with the corresponding conntrack
original direction tuple fields. See the documentation for
ct above, for more information about connection tracking, or
ovs-fields(7) for details about the connection tracking
fields.
This flag requires a valid connection tracking state as a
match prerequisite in the flow where this action is placed.
Examples of valid connection tracking state matches include
ct_state=+new, ct_state=+est, ct_state=+rel, and
ct_state=+trk-inv.
The changes, if any, to the input port and connection tracking
fields are just for searching the flow table. The changes are not
visible to actions or to later flow table lookups.
The most common use of resubmit is to visit another flow table
without port or ct, like this: resubmit(,table).
Recursive resubmit actions are permitted.
Conformance
The resubmit action is an Open vSwitch extension. However,
the goto_table instruction in OpenFlow 1.1 and later can be
viewed as a kind of restricted resubmit.
Open vSwitch 1.3 added table. Open vSwitch 2.7 added ct.
Open vSwitch imposes a limit on resubmit recursion that
varies among version:
• Open vSwitch 1.0.1 and earlier did not support
recursion.
• Open vSwitch 1.0.2 and 1.0.3 limited recursion to 8
levels.
• Open vSwitch 1.1 and 1.2 limited recursion to 16
levels.
• Open vSwitch 1.2 through 1.8 limited recursion to 32
levels.
• Open vSwitch 1.9 through 2.0 limited recursion to 64
levels.
• Open vSwitch 2.1 through 2.5 limited recursion to 64
levels and impose a total limit of 4,096 resubmits per
flow translation (earlier versions did not impose any
total limit).
• Open vSwitch 2.6 and later imposes the same limits as
2.5, with one exception: resubmit from table x to any
table y > x does not count against the recursion depth
limit.
The clone action
Syntax:
clone(action...)
Executes each nested action, saving much of the packet and
pipeline state beforehand and then restoring it afterward. The
state that is saved and restored includes all flow data and
metadata (including, for example, in_port and ct_state), the stack
accessed by push and pop actions, and the OpenFlow action set.
This action was added in Open vSwitch 2.7.
The push and pop actions
Syntax:
push:src
pop:dst
The push action pushes src on a general-purpose stack. The pop
action pops an entry off the stack into dst. src and dst should
be fields or subfields in the syntax described under Field
Specifications above.
Controllers can use the stack for saving and restoring data or
metadata around resubmit actions, for swapping or rearranging data
and metadata, or for other purposes. Any data or metadata field,
or part of one, may be pushed, and any modifiable field or
subfield may be popped.
The number of bits pushed in a stack entry do not have to match
the number of bits later popped from that entry. If more bits are
popped from an entry than were pushed, then the entry is
conceptually left-padded with 0-bits as needed. If fewer bits are
popped than pushed, then bits are conceptually trimmed from the
left side of the entry.
The stack’s size is limited. The limit is intended to be high
enough that normal use will not pose problems. Stack overflow or
underflow is an error that stops action execution (see Stack too
deep under Error Handling, above).
Examples:
• push:reg2[0..5] or push:NXM_NX_REG2[0..5] pushes on the stack
the 6 bits in register 2 bits 0 through 5.
• pop:reg2[0..5] or pop:NXM_NX_REG2[0..5] pops the value from
top of the stack and copy bits 0 through 5 of that value into
bits 0 through 5 of register 2.
Conformance
Open vSwitch 1.2 introduced push and pop as OpenFlow
extension actions.
The exit action
Syntax:
exit
This action causes Open vSwitch to immediately halt execution of
further actions. Actions which have already been executed are
unaffected. Any further actions, including those which may be in
other tables, or different levels of the resubmit call stack, are
ignored. However, an exit action within a group bucket terminates
only execution of that bucket, not other buckets or the overall
pipeline. Actions in the action set are still executed (specify
clear_actions before exit to discard them).
The multipath action
Syntax:
multipath(fields,basis,algorithm,n_links,arg,dst)
Hashes fields using basis as a universal hash parameter, then the
applies multipath link selection algorithm (with parameter arg) to
choose one of n_links output links numbered 0 through n_links
minus 1, and stores the link into dst, which must be a field or
subfield in the syntax described under Field Specifications above.
The bundle or bundle_load actions are usually easier to use than
multipath.
fields must be one of the following:
eth_src
Hashes Ethernet source address only.
symmetric_l4
Hashes Ethernet source, destination, and type, VLAN ID,
IPv4/IPv6 source, destination, and protocol, and TCP or
SCTP (but not UDP) ports. The hash is computed so that
pairs of corresponding flows in each direction hash to
the same value, in environments where L2 paths are the
same in each direction. UDP ports are not included in
the hash to support protocols such as VXLAN that use
asymmetric ports in each direction.
symmetric_l3l4
Hashes IPv4/IPv6 source, destination, and protocol, and
TCP or SCTP (but not UDP) ports. Like symmetric_l4,
this is a symmetric hash, but by excluding L2 headers it
is more effective in environments with asymmetric L2
paths (e.g. paths involving VRRP IP addresses on a
router). Not an effective hash function for protocols
other than IPv4 and IPv6, which hash to a constant zero.
symmetric_l3l4+udp
Like symmetric_l3l4+udp, but UDP ports are included in
the hash. This is a more effective hash when asymmetric
UDP protocols such as VXLAN are not a consideration.
symmetric_l3
Hashes network source address and network destination
address.
nw_src Hashes network source address only.
nw_dst Hashes network destination address only.
The algorithm used to compute the final result link must be one of
the following:
modulo_n
Computes link = hash(flow) % n_links.
This algorithm redistributes all traffic when n_links
changes. It has O(1) performance.
Use 65535 for max_link to get a raw hash value.
This algorithm is specified by RFC 2992.
hash_threshold
Computes link = hash(flow) / (MAX_HASH / n_links).
Redistributes between one-quarter and one-half of
traffic when n_links changes. It has O(1) performance.
This algorithm is specified by RFC 2992.
hrw (Highest Random Weight)
Computes the following:
for i in [0, n_links]:
weights[i] = hash(flow, i)
link = { i such that weights[i] >= weights[j] for all j != i }
Redistributes 1 / n_links of traffic when n_links
changes. It has O(n_links) performance. If n_links is
greater than a threshold (currently 64, but subject to
change), Open vSwitch will substitute another algorithm
automatically.
This algorithm is specified by RFC 2992.
iter_hash (Iterative Hash)
Computes the following:
i = 0
repeat:
i = i + 1
link = hash(flow, i) % arg
while link > max_link
Redistributes 1 / n_links of traffic when n_links
changes. O(1) performance when arg / max_link is
bounded by a constant.
Redistributes all traffic when arg changes.
arg must be greater than max_link and for best
performance should be no more than approximately
max_link * 2. If arg is outside the acceptable range,
Open vSwitch will automatically substitute the least
power of 2 greater than max_link.
This algorithm is specific to Open vSwitch.
Only the iter_hash algorithm uses arg.
It is an error if max_link is greater than or equal to 2**n_bits.
Conformance
This is an OpenFlow extension added in Open vSwitch 1.1.
The conjunction action
Syntax:
conjunction(id, k/n)
This action allows for sophisticated conjunctive match flows.
Refer to Conjunctive Match Fields in ovs-fields(7) for details.
A flow that has one or more conjunction actions may not have any
other actions except for note actions.
Conformance
Open vSwitch 2.4 introduced the conjunction action and
conj_id field. They are Open vSwitch extensions to
OpenFlow.
The note action
Syntax:
note:[hh]...
This action does nothing at all. OpenFlow controllers may use it
to annotate flows with more data than can fit in a flow cookie.
The action may include any number of bytes represented as hex
digits hh. Periods may separate pairs of hex digits, for
readability. The note action’s format doesn’t include an exact
length for its payload, so the provided bytes will be padded on
the right by enough bytes with value 0 to make the total number 6
more than a multiple of 8.
Conformance
This action is an extension to OpenFlow introduced in Open
vSwitch 1.1.
The sample action
Syntax:
sample(argument...)
Samples packets and sends one sample for every sampled packet.
The following argument forms are accepted:
probability=packets
The number of sampled packets out of 65535. Must be
greater or equal to 1.
collector_set_id=id
The unsigned 32-bit integer identifier of the set of
sample collectors to send sampled packets to. Defaults
to 0.
obs_domain_id=value
When sending samples to IPFIX collectors, the unsigned
32-bit integer Observation Domain ID sent in every IPFIX
flow record. The value may be specified as a 32-bit
integer or a field or subfield in the syntax described
under Field Specifications above. Defaults to 0.
obs_point_id=value
When sending samples to IPFIX collectors, the unsigned
32-bit integer Observation Point ID sent in every IPFIX
flow record. The value may be specified as a 32-bit
integer or a field or subfield in the syntax described
under Field Specifications above. Defaults to 0.
sampling_port=port
Sample packets on port, which should be the ingress or
egress port. This option, which was added in Open
vSwitch 2.6, allows the IPFIX implementation to export
egress tunnel information.
ingress
egress Specifies explicitly that the packet is being sampled on
ingress to or egress from the switch. IPFIX reports
sent by Open vSwitch before version 2.6 did not include
a direction. From 2.6 until 2.7, IPFIX reports inferred
a direction from sampling_port: if it was the packet’s
output port, then the direction was reported as egress,
otherwise as ingress. Open vSwitch 2.7 introduced these
options, which allow the inferred direction to be
overridden. This is particularly useful when the
ingress (or egress) port is not a tunnel.
Refer to ovs-vswitchd.conf.db(5) for more details on configuring
sample collector sets.
Conformance
This action is an OpenFlow extension added in Open vSwitch
2.4.
Support for subfields in obs_domain_id and obs_point_id was
added in Open vSwitch 3.4.
Every version of OpenFlow includes actions. OpenFlow 1.1
introduced the higher-level, related concept of instructions. In
OpenFlow 1.1 and later, actions within a flow are always
encapsulated within an instruction. Each flow has at most one
instruction of each kind, which are executed in the following
fixed order defined in the OpenFlow specification:
1. Meter
2. Apply-Actions
3. Clear-Actions
4. Write-Actions
5. Write-Metadata
6. Stat-Trigger (not supported by Open vSwitch)
7. Goto-Table
The most important instruction is Apply-Actions. This instruction
encapsulates any number of actions, which the instruction
executes. Open vSwitch does not explicitly represent
Apply-Actions. Instead, any action by itself is implicitly part
of an Apply-Actions instructions.
Open vSwitch syntax requires other instructions, if present, to be
in the order listed above. Otherwise it will flag an error.
The meter action and instruction
Syntax:
meter:meter_id
Apply meter meter_id. If a meter band rate is exceeded, the
packet may be dropped, or modified, depending on the meter band
type.
Conformance
OpenFlow 1.3 introduced the meter instruction. OpenFlow
1.5 changes meter from an instruction to an action.
OpenFlow 1.5 allows implementations to restrict meter to be
the first action in an action list and to exclude meter
from action sets, for better compatibility with OpenFlow
1.3 and 1.4. Open vSwitch restricts the meter action both
ways.
Open vSwitch 2.0 introduced OpenFlow protocol support for
meters, but it did not include a datapath implementation.
Open vSwitch 2.7 added meter support to the userspace
datapath. Open vSwitch 2.10 added meter support to the
kernel datapath. Open vSwitch 2.12 added support for meter
as an action in OpenFlow 1.5.
The clear_actions instruction
Syntax:
clear_actions
Clears the action set. See Action Sets, above, for more
information.
Conformance
OpenFlow 1.1 introduced clear_actions. Open vSwitch 2.1
added support for clear_actions.
The write_actions instruction
Syntax:
write_actions(action...)
Adds each action to the action set. The action set is carried
between flow tables and then executed at the end of the pipeline.
Only certain actions may be written to the action set. See Action
Sets, above, for more information.
Conformance
OpenFlow 1.1 introduced write_actions. Open vSwitch 2.1
added support for write_actions.
The write_metadata instruction
Syntax:
write_metadata:value[/mask]
Updates the flow’s metadata field. If mask is omitted, metadata
is set exactly to value; if mask is specified, then a 1-bit in
mask indicates that the corresponding bit in metadata will be
replaced with the corresponding bit from value. Both value and
mask are 64-bit values that are decimal by default; use a 0x
prefix to specify them in hexadecimal.
The metadata field can also be matched in the flow table and
updated with actions such as set_field and move.
Conformance
OpenFlow 1.1 introduced write_metadata. Open vSwitch 2.1
added support for write_metadata.
The goto_table instruction
Syntax:
goto_table:table
Jumps to table as the next table in the process pipeline. The
table may be a number between 0 and 254 or a table name.
It is an error if table is less than or equal to the table of the
flow that contains it; that is, goto_table must move forward in
the OpenFlow pipeline. Since goto_table must be the last
instruction in a flow, it never leads to recursion. The resubmit
extension action is more flexible.
Conformance
OpenFlow 1.1 introduced goto_table. Open vSwitch 2.1 added
support for goto_table.
The Open vSwitch Development Community
2016-2024, The Open vSwitch Development Community
This page is part of the Open vSwitch (a distributed virtual
multilayer switch) project. Information about the project can be
found at ⟨http://openvswitch.org/⟩. If you have a bug report for
this manual page, send it to bugs@openvswitch.org. This page was
obtained from the project's upstream Git repository
⟨https://github.com/openvswitch/ovs.git⟩ on 2025-08-11. (At that
time, the date of the most recent commit that was found in the
repository was 2025-07-31.) If you discover any rendering
problems in this HTML version of the page, or you believe there is
a better or more up-to-date source for the page, or you have
corrections or improvements to the information in this COLOPHON
(which is not part of the original manual page), send a mail to
man-pages@man7.org
3.6.90 Aug 09, 2025 OVS-ACTIONS(7)
Pages that refer to this page: ovn-nb(5), ovn-sb(5), ovs-vswitchd.conf.db(5), ovs-flowviz(8), ovs-ofctl(8)
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