ovs-actions(7) Open vSwitch Manual 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.
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, and decap
of other types of packets is unsupported and also
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.
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.
Theoutputaction
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.
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.
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"
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.
Thecontrolleraction
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.
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.
Theenqueueaction
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 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.
Thebundleandbundle_loadactions
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.
Thegroupaction
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.
Thestrip_vlanandpopactions
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.
Thepush_vlanaction
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.
Thepush_mplsaction
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.
Thepop_mplsaction
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.
Theencapaction
Syntax:
encap(nsh([md_type=md_type], [tlv(class,type,value)]...))
encap(ethernet)
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.
Conformance:
This action is an Open vSwitch extension to OpenFlow 1.3 and
later, introduced in Open vSwitch 2.8.
Thedecapaction
Syntax:
decap
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, 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.
These actions modify packet data and metadata fields.
Theset_fieldandloadactions
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.
Themoveaction
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.
Themod_dl_srcandmod_dl_dstactions
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,
Themod_nw_srcandmod_nw_dstactions
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,
Themod_nw_tosandmod_nw_ecnactions
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,
Themod_tp_srcandmod_tp_dstactions
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,
Thedec_ttlaction
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.
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 an IPv4 or
IPv6 header. See ``Inconsistencies’’, above, for more
information.
Conformance:
All versions of OpenFlow and Open vSwitch support this action.
Theset_mpls_label,set_mpls_tc, andset_mpls_ttlactions
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,
Thedec_mpls_ttlanddec_nsh_ttlactions
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.
Thecheck_pkt_largeraction
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 2.11.90.
Thedelete_fieldaction
Syntax:
delete_field:field
The delete_field action deletes a field in the syntax described
under ``Field Specifications’’ above. Currently, only the
tun_metadta fields are supported.
This action was added in Open vSwitch 2.13.90.
Theset_tunnelaction
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.
Theset_queueandpop_queueactions
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: ⟨https://
mailman.stanford.edu/pipermail/openflow-spec/2009-August/
000394.html⟩
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.
Thectaction
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 userspace datapath only supports
the hash behavior.
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.
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
⟨http://www.netfilter.org/news.html#2012-04-03⟩ .
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.
Thect_clearaction
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 2.6.90.
Thelearnaction
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 ``Header
Modification’’ 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 1.5.90.
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 ⟨https://
mail.openvswitch.org/pipermail/ovs-discuss/
2016-June/021694.html⟩ .
• 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.
Thefin_timeoutaction
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
1.5.90.
Theresubmitaction
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 1.2.90 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.
Thecloneaction
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 2.6.90.
Thepushandpopactions
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.
Theexitaction
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).
Themultipathaction
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.
Theconjunctionaction
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.
Thenoteaction
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.
Thesampleaction
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=id
When sending samples to IPFIX collectors, the
unsigned 32-bit integer Observation Domain ID sent
in every IPFIX flow record. Defaults to 0.
obs_point_id=id
When sending samples to IPFIX collectors, the
unsigned 32-bit integer Observation Point ID sent
in every IPFIX flow record. 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 2.5.90, 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 2.5.90
did not include a direction. From 2.5.90 until
2.6.90, 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 2.6.90 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.
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.
Themeteraction 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.
Theclear_actionsinstruction
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.
Thewrite_actionsinstruction
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.
Thewrite_metadatainstruction
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.
Thegoto_tableinstruction
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.
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 2020-12-18. (At that
time, the date of the most recent commit that was found in the
repository was 2020-12-16.) 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
Open vSwitch 2.14.90 ovs-actions(7)
Pages that refer to this page: ovs-vswitchd.conf.db(5), ovs-ofctl(8)
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