This document aims to comprehensively document all of the OpenFlow actions and instructions, both standard and non-standard, supported by Open vSwitch, regardless of origin46 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 message46
In this document, we define an action as an OpenFlow action, which is a kind of command that specifies what to do with a packet46 Actions are used in OpenFlow flows to describe what to do when the flow matches a packet, and in a few other places in OpenFlow46 Each version of the OpenFlow specification defines standard actions, and beyond that many OpenFlow switches, including Open vSwitch, implement extensions to the standard46
OpenFlow groups actions in two ways: as an action list or an action set, described below46
Action Lists
An action list, a concept present in every version of OpenFlow, is simply an ordered sequence of actions46 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 1460, section 3463], with one exception: when an action list outputs multiple packets, the switch may output the packets in an order different from that specified46 Usually, this exception is not important, especially in the common case when the packets are output to different ports46
Action Sets
OpenFlow 1461 introduced the concept of an action set46 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 specifications46 Because of these semantics, some standard OpenFlow actions cannot usefully be included in an action set46 For some, but not all, Open vSwitch extension actions, Open vSwitch defines its own action set semantics and ordering46
The OpenFlow pipeline has an action set associated with it as a packet is processed46 After pipeline processing is otherwise complete, the switch executes the actions in the action set46
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:
An action set may only contain the actions listed above46
Packet processing can encounter a variety of errors:
OpenFlow 1460 allows any action to be part of any flow, regardless of the flow's match46 Some combinations do not make sense, e46g46 an set_nw_tos action in a flow that matches only ARP packets or strip_vlan in a flow that matches packets without VLAN tags46 Other combinations have varying results depending on the kind of packet that the flow processes, e46g46 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 packet46 Nevertheless OVS allows all of the above in conformance with OpenFlow 1460, 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:1462463464
Open vSwitch calls these kinds of combinations inconsistencies between match and actions46 OpenFlow 1461 and later forbid inconsistencies, and disallow the examples described above by preventing such flows from being added46 All of the above, for example, will fail with an error message if one replaces OpenFlow10 by OpenFlow1146
OpenFlow 1461 and later cannot detect and disallow all inconsistencies46 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 execute46 Thus, actions with write_actions and some other contexts are exempt from consistency requirements46
When OVS executes an action inconsistent with the packet, it treats it as a no-op46
Open vSwitch supports multiple OpenFlow versions simultaneously on a single switch46 When actions are added with one OpenFlow version and then retrieved with another, Open vSwitch does its best to translate between them46
Inter-version compatibility issues can still arise when different connections use different OpenFlow versions46 Backward compatibility is the most obvious case46 Suppose, for example, that an OpenFlow 1461 session adds a flow with a push_vlan action, for which there is no equivalent in OpenFlow 146046 If an OpenFlow 1460 session retrieves this flow, Open vSwitch must somehow represent the action46
Forward compatibility can also be an issue, because later OpenFlow versions sometimes remove functionality46 The best example is the enqueue action from OpenFlow 1460, which OpenFlow 1461 removed46
In practice, Open vSwitch uses a variety of strategies for inter-version compatibility:
Perfect inter-version compatibility is not possible, so best results require OpenFlow connections to use a consistent version46 One may enforce use of a particular version by setting the protocols column for a bridge, e46g46 to force br0 to use only OpenFlow 1463:
ovs-vsctl set bridge br0 protocols=OpenFlow13
Many Open vSwitch actions refer to fields46 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_DST46 Before Open vSwitch 2467, only OXM or NXM field names were accepted46
Many actions that act on fields can also act on subfields, that is, parts of fields, written as field[start4646end], where start is the first bit and end is the last bit to use in field, e46g46 vlan_tci[13464615] for the VLAN PCP46 A single-bit subfield may also be written as field[offset], e46g46 vlan_tci[13] for the least-significant bit of the VLAN PCP46 Empty brackets may be used to explicitly designate an entire field, e46g46 vlan_tci[] for the entire 16-bit VLAN TCI header46 Before Open vSwitch 2467, brackets were required in field specifications46
See ovs-fields(7) for a list of fields and their names46
Many Open vSwitch actions refer to OpenFlow ports46 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 ports46 OpenFlow 1461 and later use 32-bit port numbers, but Open vSwitch never assigns a port number that requires more than 16 bits46
In most contexts, the name of a port may also be used46 (The most obvious context where a port name may not be used is in an ovs-ofctl command along with the --no-names option46) 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])46
Open vSwitch also supports the following standard OpenFlow port names (even in contexts where port names are not otherwise supported)46 The corresponding OpenFlow 1460 and 1461+ port numbers are listed alongside them but should not be used in flow syntax:
These actions send a packet to a physical port or a controller46 A packet that never encounters an output action on its trip through the Open vSwitch pipeline is effectively dropped46 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 effect46
Outputs the packet to an OpenFlow port most commonly specified as port46 Alternatively, the output port may be read from field, a field or subfield in the syntax described under ``Field Specifications'' above46 Either way, if the port is the packet's input port, the packet is not output46
The port may be one of the following standard OpenFlow ports:
The port may also be one of the following additional OpenFlow ports, unless max_len is specified:
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_PORT46
With max_len, the packet is truncated to at most nbytes bytes before being output46 In this case, the output port may not be a patch port46 Truncation is just for the single output action, so that later actions in the OpenFlow pipeline work with the complete packet46 The truncation feature is meant for use in monitoring applications, e46g46 for mirroring packets to a collector46
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 action46 All versions of Open vSwitch treat such an action as a no-op46 If a port with the number is created later, then the action will be honored at that point46 (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 time46)
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)46 When output is disabled, output actions (and other actions that output to the port) are allowed but have no effect46
Open vSwitch allows output to a port that does not exist, although OpenFlow allows switches to reject such actions46
Output to the Input Port
OpenFlow requires a switch to ignore attempts to send a packet out its ingress port in the most straightforward way46 For example, output:234 has no effect if the packet has ingress port 23446 The rationale is that dropping these packets makes it harder to loop the network46 Sometimes this behavior can even be convenient, e46g46 it is often the desired behavior in a flow that forwards a packet to several ports (``floods'' the packet)46
Sometimes one really needs to send a packet out its ingress port (``hairpin'')46 In this case, use in_port to explicitly output the packet to its input port, e46g46:
$ 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 port46 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 port46 It's difficult to take advantage of output to in_port in this situation46 To help, Open vSwitch provides, as an OpenFlow extension, the ability to modify the in_port field46 Whatever value is currently in the in_port field is both the port to which output will be dropped and the destination for in_port46 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"
All versions of OpenFlow and Open vSwitch support output to a literal port46 Output to a register is an OpenFlow extension introduced in Open vSwitch 146346 Output with truncation is an OpenFlow extension introduced in Open vSwitch 246646
Sends the packet and its metadata to an OpenFlow controller or controllers encapsulated in an OpenFlow ``packet-in'' message46 The supported options are:
All versions of OpenFlow and Open vSwitch support controller action and its max_len option46 The userdata and pause options require the Open vSwitch NXAST_CONTROLLER2 extension action added in Open vSwitch 246646 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 146646
Enqueues the packet on the specified queue within port port46
port must be an OpenFlow port number or name as described under ``Port Specifications'' above46 port may be in_port or local but the other standard OpenFlow ports are not allowed46
queue must be a a number between 0 and 4294967294 (0xfffffffe), inclusive46 The number of actually supported queues depends on the switch46 Some OpenFlow implementations do not support queuing at all46 In Open vSwitch, the supported queues vary depending on the operating system, datapath, and hardware in use46 Use the QoS and Queue tables in the Open vSwitch database to configure queuing on individual OpenFlow ports (see ovs-vswitchd46conf46db(5) for more information)46
Only OpenFlow 1460 supports enqueue46 OpenFlow 1461 added the set_queue action to use in its place along with output46
Open vSwitch translates enqueue to a sequence of three actions in OpenFlow 1461 or later: set_queue:queue, output:port, pop_queue46 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 action46
These actions choose a port (``slave'') from a comma-separated OpenFlow port list46 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'' above46
These actions hash a set of fields using basis as a universal hash parameter, then apply the bundle link selection algorithm to choose a port46
fields must be one of the following46 For the options with ``symmetric'' in the name, reversing source and destination addresses yields the same hash:
algorithm must be one of the following:
for i in [1,n_slaves]:
weights[i] = hash(flow, i)
slave = { i such that weights[i] >= weights[j] for all j != i }
The algorithms take port liveness into account when selecting slaves46 The definition of whether a port is live is subject to change46 It currently takes into account carrier status and link monitoring protocols such as BFD and CFM46 If none of the slaves is live, bundle does not output the packet and bundle_load stores OFPP_NONE (65535) in the output field46
Example: bundle(eth_src,0,hrw,ofport,slaves:4,8) uses an Ethernet source hash with basis 0, to select between OpenFlow ports 4 and 8 using the Highest Random Weight algorithm46
Open vSwitch 1462 introduced the bundle and bundle_load OpenFlow extension actions46
Outputs the packet to the OpenFlow group group, which must be a number in the range 0 to 4294967040 (0xffffff00)46 The group must exist or Open vSwitch will refuse to add the flow46 When a group is deleted, Open vSwitch also deletes all of the flows that output to it46
Groups contain action sets, whose semantics are described above in the section ``Action Sets''46 The semantics of action sets can be surprising to users who expect action list semantics, since action sets reorder and sometimes ignore actions46
A group action usually executes the action set or sets in one or more group buckets46 Open vSwitch saves the packet and metadata before it executes each bucket, and then restores it afterward46 Thus, when a group executes more than one bucket, this means that each bucket executes on the same packet and metadata46 Moreover, regardless of the number of buckets executed, the packet and metadata are the same before and after executing the group46
Sometimes saving and restoring the packet and metadata can be undesirable46 In these situations, workarounds are possible46 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 selected46 An obvious design would be for the bucket to communicate the value via set_field on a register46 This does not work because registers are part of the metadata that group saves and restores46 The following alternative bucket designs do work:
An exit action within a group bucket terminates only execution of that bucket, not other buckets or the overall pipeline46
OpenFlow 1461 introduced group46 Open vSwitch 2466 and later also supports group as an extension to OpenFlow 146046
Removes the outermost VLAN tag, if any, from the packet46
The two names for this action are synonyms with no semantic difference46 The OpenFlow 1460 specification uses the name strip_vlan and later versions use pop_vlan, but OVS accepts either name regardless of version46
In OpenFlow 1461 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)46 See ``Inconsistencies'', above, for more information46
All versions of OpenFlow and Open vSwitch support this action46
Pushes a new outermost VLAN onto the packet46 Uses TPID ethertype, which must be 0x8100 for an 802461Q C-tag or 0x88a8 for a 802461ad S-tag46
OpenFlow 1461 and later supports this action46 Open vSwitch 2468 added support for multiple VLAN tags (with a limit of 2) and 802461ad S-tags46
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 0x884846
If the packet did not already contain any MPLS labels, initializes the new LSE as:
If the packet did already contain an MPLS label, initializes the new outermost label as a copy of the existing outermost label46
OVS currently supports at most 3 MPLS labels46
This action applies only to Ethernet packets46
Open vSwitch 14611 introduced support for MPLS46 OpenFlow 1461 and later support push_mpls46 Open vSwitch implements push_mpls as an extension to OpenFlow 146046
Strips the outermost MPLS label stack entry and changes the packet's Ethertype to ethertype46
This action applies only to Ethernet packets with at least one MPLS label46 If there is more than one MPLS label, then ethertype should be an MPLS Ethertype (B0x8847 or 0x8848)46
Open vSwitch 14611 introduced support for MPLS46 OpenFlow 1461 and later support pop_mpls46 Open vSwitch implements pop_mpls as an extension to OpenFlow 146046
The encap action encapsulates a packet with a specified header46 It has variants for different kinds of encapsulation46
The encap(nsh(464646)) variant encapsulates an Ethernet frame with NSH46 The md_type may be 1 or 2 for metadata type 1 or 2, defaulting to 146 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 0x46 For example:
The encap(ethernet) variant encapsulate a bare L3 packet in an Ethernet frame46 The Ethernet type is initialized to the L3 packet's type, e46g46 0x0800 if the L3 packet is IPv446 The Ethernet source and destination are initially zeroed46
This action is an Open vSwitch extension to OpenFlow 1463 and later, introduced in Open vSwitch 246846
Removes an outermost encapsulation from the packet:
This action is an Open vSwitch extension to OpenFlow 1463 and later, introduced in Open vSwitch 246846
These actions modify packet data and metadata fields46
These actions loads a literal value into a field or part of a field46 The set_field action takes value in the customary syntax for field dst, e46g46 00:11:22:33:44:55 for an Ethernet address, and dst as the field's name46 The optional mask allows part of a field to be set46
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'' above46
The following all set the Ethernet source address to 00:11:22:33:44:55:
The following all set the multicast bit in the Ethernet destination address:
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 0x80046 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-op46
Open vSwitch 1461 introduced NXAST_REG_LOAD as a extension to OpenFlow 1460 and used load to express it46 Later, OpenFlow 1462 introduced a standard OFPAT_SET_FIELD action that was restricted to loading entire fields, so Open vSwitch added the form set_field with this restriction46 OpenFlow 1465 extended OFPAT_SET_FIELD to the point that it became a superset of NXAST_REG_LOAD46 Open vSwitch translates either syntax as necessary for the OpenFlow version in use: in OpenFlow 1460 and 1461, NXAST_REG_LOAD; in OpenFlow 1462, 1463, and 1464, NXAST_REG_LOAD for load or for loading a subfield, OFPAT_SET_FIELD otherwise; and OpenFlow 1465 and later, OFPAT_SET_FIELD46
Copies the named bits from field or subfield src to field or subfield dst46 src and dst should fields or subfields in the syntax described under ``Field Specifications'' above46 The two fields or subfields must have the same width46
Examples:
In OpenFlow 1460 through 1464, move ordinarily uses an Open vSwitch extension to OpenFlow46 In OpenFlow 1465, move uses the OpenFlow 1465 standard OFPAT_COPY_FIELD action46 The ONF has also made OFPAT_COPY_FIELD available as an extension to OpenFlow 146346 Open vSwitch 2464 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 it46
Sets the Ethernet source or destination address, respectively, to mac, which should be expressed in the form xx:xx:xx:xx:xx:xx46
For L3-only packets, that is, those that lack an Ethernet header, this action has no effect46
OpenFlow 1460 and 1461 have specialized actions for these purposes46 OpenFlow 1462 and later do not, so Open vSwitch translates them to appropriate OFPAT_SET_FIELD actions for those versions,
Sets the IPv4 source or destination address, respectively, to ip, which should be expressed in the form w46x46y46z46
In OpenFlow 1461 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, e46g46 pop_mpls:0x0800)46 See ``Inconsistencies'', above, for more information46
OpenFlow 1460 and 1461 have specialized actions for these purposes46 OpenFlow 1462 and later do not, so Open vSwitch translates them to appropriate OFPAT_SET_FIELD actions for those versions,
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 25546 This action does not modify the two least significant bits of the ToS field (the ECN bits)46
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, inclusive46 This action does not modify the six most significant bits of the field (the DSCP bits)46
In OpenFlow 1461 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)46 See ``Inconsistencies'', above, for more information46
OpenFlow 1460 has a mod_nw_tos action but not mod_nw_ecn46 Open vSwitch implements the latter in OpenFlow 1460 as an extension using NXAST_REG_LOAD46 OpenFlow 1461 has specialized actions for these purposes46 OpenFlow 1462 and later do not, so Open vSwitch translates them to appropriate OFPAT_SET_FIELD actions for those versions,
Sets the TCP or UDP or SCTP source or destination port, respectively, to port46 Both IPv4 and IPv6 are supported46
In OpenFlow 1461 and later, consistency rules allow these actions only in a flow that matches only packets that contain a TCP or UDP or SCTP header46 See ``Inconsistencies'', above, for more information46
OpenFlow 1460 and 1461 have specialized actions for these purposes46 OpenFlow 1462 and later do not, so Open vSwitch translates them to appropriate OFPAT_SET_FIELD actions for those versions,
Decrement TTL of IPv4 packet or hop limit of IPv6 packet46 If the TTL or hop limit is initially 0 or 1, no decrement occurs, as packets reaching TTL zero must be rejected46 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 actions46 (However, if the current set of actions was reached through resubmit, the remaining actions in outer levels resume processing46)
As an Open vSwitch extension to OpenFlow, this action supports the ability to specify a list of controller IDs46 Open vSwitch will only send the message to controllers with the given ID or IDs46 Specifying no list is equivalent to specifying a single controller ID of zero46
Sets the TCP or UDP or SCTP source or destination port, respectively, to port46 Both IPv4 and IPv6 are supported46
In OpenFlow 1461 and later, consistency rules allow these actions only in a flow that matches only packets that contain an IPv4 or IPv6 header46 See ``Inconsistencies'', above, for more information46
All versions of OpenFlow and Open vSwitch support this action46
The set_mpls_label action sets the label of the packet's outer MPLS label stack entry46 label should be a 20-bit value that is decimal by default; use a 0x prefix to specify the value in hexadecimal46
The set_mpls_tc action sets the traffic class of the packet's outer MPLS label stack entry46 tc should be in the range 0 to 7, inclusive46
The set_mpls_ttl action sets the TTL of the packet's outer MPLS label stack entry46 ttl should be in the range 0 to 255 inclusive46
In OpenFlow 1461 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, e46g46 push_mpls:0x8847)46 See ``Inconsistencies'', above, for more information46
OpenFlow 1460 does not support MPLS, but Open vSwitch implements these actions as extensions46 OpenFlow 1461 has specialized actions for these purposes46 OpenFlow 1462 and later do not, so Open vSwitch translates them to appropriate OFPAT_SET_FIELD actions for those versions,
These actions decrement the TTL of the packet's outer MPLS label stack entry or its NSH header, respectively46 If the TTL is initially 0 or 1, no decrement occurs46 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 them46 Processing the current set of actions then stops46 (However, if the current set of actions was reached through resubmit, remaining actions in outer levels resume processing46)
In OpenFlow 1461 and later, consistency rules allow this actions only in a flow that matches only packets that contain an MPLS label or an NSH header, respectively46 See ``Inconsistencies'', above, for more information46
Open vSwitch 14611 introduced support for MPLS46 OpenFlow 1461 and later support dec_mpls_ttl46 Open vSwitch implements dec_mpls_ttl as an extension to OpenFlow 146046
Open vSwitch 2468 introduced support for NSH, although the NSH draft changed after release so that only Open vSwitch 2469 and later conform to the final protocol specification46 The dec_nsh_ttl action and NSH support in general is an Open vSwitch extension not supported by any version of OpenFlow46
Checks if the packet is larger than the specified length in pkt_len46 If so, stores 1 in dst, which should be a 1-bit field; if not, stores 046
The packet length to check againt the argument pkt_len includes the L2 header and L2 payload of the packet, but not the VLAN tag (if present)46
Examples:
This action was added in Open vSwitch 24611469046
Many kinds of tunnels support a tunnel ID, e46g46 VXLAN and Geneve have a 24-bit VNI, and GRE has an optional 32-bit key46 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 configuration46 See the tunnel ID documentation in ovs-fields(7) for more information46
These actions are OpenFlow extensions46 set_tunnel was introduced in Open vSwitch 146046 set_tunnel64, which is needed if id is wider than 32 bits, was added in Open vSwitch 146146 Both actions always set the entire tunnel ID field46
Open vSwitch supports these actions in all versions of OpenFlow, but in OpenFlow 1462 and later it translates them to an appropriate standardized OFPAT_SET_FIELD action46
The set_queue action sets the queue ID to be used for subsequent output actions to queue, which must be a 32-bit integer46 The range of meaningful values of queue, and their meanings, varies greatly from one OpenFlow implementation to another46 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-wise46 For more information, see the documentation for the output queue field in ovs-fields(7)46
The pop_queue restores the output queue to the default that was set when the packet entered the switch (generally 0)46
Four billion queues ought to be enough for anyone: <URL: https://mailman.stanford.edu/pipermail/openflow-spec/2009-August/000394.html >
OpenFlow 1461 introduced the set_queue action46 Open vSwitch also supports it as an extension in OpenFlow 146046
The pop_queue action is an Open vSwitch extension46
Open vSwitch is often used to implement a firewall46 The preferred way to implement a firewall is ``connection tracking,'' that is, to keep track of the connection state of individual TCP sessions46 The ct action described in this section, added in Open vSwitch 2465, implements connection tracking46 For new deployments, it is the recommended way to implement firewalling with Open vSwitch46
Before ct was added, Open vSwitch did not have built-in support for connection tracking46 Instead, Open vSwitch supported the learn action, which allows a received packet to add a flow to an OpenFlow flow table46 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 direction46 The additional fin_timeout action allowed the learned flows to expire quickly after TCP session termination46
The action has two modes of operation, distinguished by whether commit is present46 The following arguments may be present in either mode:
Without commit, this action sends the packet through the connection tracker46 The connection tracker keeps track of the state of TCP connections for packets passed through it46 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)46
In this form, ct forks the OpenFlow pipeline:
Without commit, the ct action accepts the following arguments:
With commit, the connection tracker commits the connection to the connection tracking module46 The commit flag should only be used from the pipeline within the first fork of ct without commit46 Information about the connection is stored beyond the lifetime of the packet in the pipeline46 Some ct_state flags are only available for committed connections46
The following options are available only with commit:
With the Linux datapath, global sysctl options affect ct behavior46 In particular, if net46netfilter46nf_conntrack_helper is enabled, which it is by default until Linux 4467, then application layer gateway helpers may be executed even if alg is not specified46 For security reasons, the netfilter team recommends users disable this option46 For further details, please see <URL: http://www.netfilter.org/news.html#2012-04-03 > 46
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 connections46 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 size46 Reassembly occurs within the context of the zone, meaning that IP fragments in different zones are not assembled together46 Pipeline processing for the initial fragments is halted46 When the final fragment is received, the message is assembled and pipeline processing continues for that flow46 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)46 As such, it is strongly recommended that multiple flows should not execute ct to reassemble fragments from the same IP message46
The ct action was introduced in Open vSwitch 246546 Some of its features were introduced later, noted individually above46
Clears connection tracking state from the flow, zeroing ct_state, ct_zone, ct_mark, and ct_label46
This action was introduced in Open vSwitch 2466469046
The learn action adds or modifies a flow in an OpenFlow table, similar to ovs-ofctl --strict mod-flows46 The arguments specify the match fields, actions, and other properties of the flow to be added or modified46
Match fields for the new flow are specified as follows46 At least one match field should ordinarily be specified:
The field and src arguments above should be fields or subfields in the syntax described under ``Field Specifications'' above46
Match field specifications must honor prerequisites for both the flow with the learn and the new flow that it creates46 Consider the following complete flow, in the syntax accepted by ovs-ofctl46 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_src46 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_dst46 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 follows46 At least one action should ordinarily be specified:
The following additional arguments are optional:
By itself, the learn action can only put two kinds of actions into the flows that it creates: load and output actions46 If learn is used in isolation, these are severe limits46
However, learn is not meant to be used in isolation46 It is a primitive meant to be used together with other Open vSwitch features to accomplish a task46 Its existing features are enough to accomplish most tasks46
Here is an outline of a typical pipeline structure that allows for versatile behavior using learn:
This approach can be used to implement many learn-based features46 For example:
The learn action is an Open vSwitch extension to OpenFlow added in Open vSwitch 146346 Some features of learn were added in later versions, as noted individually above46
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 flag46 When such a packet is observed, the action reduces the rule's timeouts to those specified on the action46 If the rule's existing timeout is already shorter than the one that the action specifies, then that timeout is unaffected46
The timeouts are specified as key-value pairs:
This action is normally added to a learned flow by the learn action46 It is unlikely to be useful otherwise46
This Open vSwitch extension action was added in Open vSwitch 1465469046
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 entry46 Arguments can customize the search:
The changes, if any, to the input port and connection tracking fields are just for searching the flow table46 The changes are not visible to actions or to later flow table lookups46
The most common use of resubmit is to visit another flow table without port or ct, like this: resubmit(,table)46
Recursive resubmit actions are permitted46
The resubmit action is an Open vSwitch extension46 However, the goto_table instruction in OpenFlow 1461 and later can be viewed as a kind of restricted resubmit46
Open vSwitch 14624690 added table46 Open vSwitch 2467 added ct46
Open vSwitch imposes a limit on resubmit recursion that varies among version:
Executes each nested action, saving much of the packet and pipeline state beforehand and then restoring it afterward46 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 set46
This action was added in Open vSwitch 2466469046
The push action pushes src on a general-purpose stack46 The pop action pops an entry off the stack into dst46 src and dst should be fields or subfields in the syntax described under ``Field Specifications'' above46
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 purposes46 Any data or metadata field, or part of one, may be pushed, and any modifiable field or subfield may be popped46
The number of bits pushed in a stack entry do not have to match the number of bits later popped from that entry46 If more bits are popped from an entry than were pushed, then the entry is conceptually left-padded with 0-bits as needed46 If fewer bits are popped than pushed, then bits are conceptually trimmed from the left side of the entry46
The stack's size is limited46 The limit is intended to be high enough that ``normal'' use will not pose problems46 Stack overflow or underflow is an error that stops action execution (see ``Stack too deep'' under ``Error Handling'', above)46
Examples:
Open vSwitch 1462 introduced push and pop as OpenFlow extension actions46
This action causes Open vSwitch to immediately halt execution of further actions46 Actions which have already been executed are unaffected46 Any further actions, including those which may be in other tables, or different levels of the resubmit call stack, are ignored46 However, an exit action within a group bucket terminates only execution of that bucket, not other buckets or the overall pipeline46 Actions in the action set are still executed (specify clear_actions before exit to discard them)46
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'' above46
The bundle or bundle_load actions are usually easier to use than multipath46
fields must be one of the following:
The algorithm used to compute the final result link must be one of 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 }
i = 0
repeat:
i = i + 1
link = hash(flow, i) % arg
while link > max_link
Only the iter_hash algorithm uses arg46
It is an error if max_link is greater than or equal to 2**n_bits46
This is an OpenFlow extension added in Open vSwitch 146146
This action allows for sophisticated ``conjunctive match'' flows46 Refer to ``Conjunctive Match Fields'' in ovs-fields(7) for details46
A flow that has one or more conjunction actions may not have any other actions except for note actions46
Open vSwitch 2464 introduced the conjunction action and conj_id field46 They are Open vSwitch extensions to OpenFlow46
This action does nothing at all46 OpenFlow controllers may use it to annotate flows with more data than can fit in a flow cookie46
The action may include any number of bytes represented as hex digits hh46 Periods may separate pairs of hex digits, for readability46 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 846
This action is an extension to OpenFlow introduced in Open vSwitch 146146
Samples packets and sends one sample for every sampled packet46
The following argument forms are accepted:
Refer to ovs-vswitchd46conf46db(5) for more details on configuring sample collector sets46
This action is an OpenFlow extension added in Open vSwitch 246446
Every version of OpenFlow includes actions46 OpenFlow 1461 introduced the higher-level, related concept of instructions46 In OpenFlow 1461 and later, actions within a flow are always encapsulated within an instruction46 Each flow has at most one instruction of each kind, which are executed in the following fixed order defined in the OpenFlow specification:
The most important instruction is Apply-Actions46 This instruction encapsulates any number of actions, which the instruction executes46 Open vSwitch does not explicitly represent Apply-Actions46 Instead, any action by itself is implicitly part of an Apply-Actions instructions46
Open vSwitch syntax requires other instructions, if present, to be in the order listed above46 Otherwise it will flag an error46
Apply meter meter_id46 If a meter band rate is exceeded, the packet may be dropped, or modified, depending on the meter band type46
OpenFlow 1463 introduced the meter instruction46 OpenFlow 1465 changes meter from an instruction to an action46
OpenFlow 1465 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 1463 and 146446 Open vSwitch restricts the meter action both ways46
Open vSwitch 2460 introduced OpenFlow protocol support for meters, but it did not include a datapath implementation46 Open vSwitch 2467 added meter support to the userspace datapath46 Open vSwitch 24610 added meter support to the kernel datapath46 Open vSwitch 24612 added support for meter as an action in OpenFlow 146546
Clears the action set46 See ``Action Sets'', above, for more information46
OpenFlow 1461 introduced clear_actions46 Open vSwitch 2461 added support for clear_actions46
Adds each action to the action set46 The action set is carried between flow tables and then executed at the end of the pipeline46 Only certain actions may be written to the action set46 See ``Action Sets'', above, for more information46
OpenFlow 1461 introduced write_actions46 Open vSwitch 2461 added support for write_actions46
Updates the flow's metadata field46 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 value46 Both value and mask are 64-bit values that are decimal by default; use a 0x prefix to specify them in hexadecimal46
The metadata field can also be matched in the flow table and updated with actions such as set_field and move46
OpenFlow 1461 introduced write_metadata46 Open vSwitch 2461 added support for write_metadata46
Jumps to table as the next table in the process pipeline46 The table may be a number between 0 and 254 or a table name46
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 pipeline46 Since goto_table must be the last instruction in a flow, it never leads to recursion46 The resubmit extension action is more flexible46
OpenFlow 1461 introduced goto_table46 Open vSwitch 2461 added support for goto_table46