+Asynchronous Messages
+=====================
+
+Over time, Open vSwitch has added many knobs that control whether a
+given controller receives OpenFlow asynchronous messages. This
+section describes how all of these features interact.
+
+First, a service controller never receives any asynchronous messages
+unless it changes its miss_send_len from the service controller
+default of zero in one of the following ways:
+
+ - Sending an OFPT_SET_CONFIG message with nonzero miss_send_len.
+
+ - Sending any NXT_SET_ASYNC_CONFIG message: as a side effect, this
+ message changes the miss_send_len to
+ OFP_DEFAULT_MISS_SEND_LEN (128) for service controllers.
+
+Second, OFPT_FLOW_REMOVED and NXT_FLOW_REMOVED messages are generated
+only if the flow that was removed had the OFPFF_SEND_FLOW_REM flag
+set.
+
+Third, OFPT_PACKET_IN and NXT_PACKET_IN messages are sent only to
+OpenFlow controller connections that have the correct connection ID
+(see "struct nx_controller_id" and "struct nx_action_controller"):
+
+ - For packet-in messages generated by a NXAST_CONTROLLER action,
+ the controller ID specified in the action.
+
+ - For other packet-in messages, controller ID zero. (This is the
+ default ID when an OpenFlow controller does not configure one.)
+
+Finally, Open vSwitch consults a per-connection table indexed by the
+message type, reason code, and current role. The following table
+shows how this table is initialized by default when an OpenFlow
+connection is made. An entry labeled "yes" means that the message is
+sent, an entry labeled "---" means that the message is suppressed.
+
+ master/
+ message and reason code other slave
+ ---------------------------------------- ------- -----
+ OFPT_PACKET_IN / NXT_PACKET_IN
+ OFPR_NO_MATCH yes ---
+ OFPR_ACTION yes ---
+ OFPR_INVALID_TTL --- ---
+
+ OFPT_FLOW_REMOVED / NXT_FLOW_REMOVED
+ OFPRR_IDLE_TIMEOUT yes ---
+ OFPRR_HARD_TIMEOUT yes ---
+ OFPRR_DELETE yes ---
+
+ OFPT_PORT_STATUS
+ OFPPR_ADD yes yes
+ OFPPR_DELETE yes yes
+ OFPPR_MODIFY yes yes
+
+The NXT_SET_ASYNC_CONFIG message directly sets all of the values in
+this table for the current connection. The
+OFPC_INVALID_TTL_TO_CONTROLLER bit in the OFPT_SET_CONFIG message
+controls the setting for OFPR_INVALID_TTL for the "master" role.
+
+
+OFPAT_ENQUEUE
+=============
+
+The OpenFlow 1.0 specification requires the output port of the OFPAT_ENQUEUE
+action to "refer to a valid physical port (i.e. < OFPP_MAX) or OFPP_IN_PORT".
+Although OFPP_LOCAL is not less than OFPP_MAX, it is an 'internal' port which
+can have QoS applied to it in Linux. Since we allow the OFPAT_ENQUEUE to apply
+to 'internal' ports whose port numbers are less than OFPP_MAX, we interpret
+OFPP_LOCAL as a physical port and support OFPAT_ENQUEUE on it as well.
+
+
+OFPT_FLOW_MOD
+=============
+
+The OpenFlow specification for the behavior of OFPT_FLOW_MOD is
+confusing. The following tables summarize the Open vSwitch
+implementation of its behavior in the following categories:
+
+ - "match on priority": Whether the flow_mod acts only on flows
+ whose priority matches that included in the flow_mod message.
+
+ - "match on out_port": Whether the flow_mod acts only on flows
+ that output to the out_port included in the flow_mod message (if
+ out_port is not OFPP_NONE). OpenFlow 1.1 and later have a
+ similar feature (not listed separately here) for out_group.
+
+ - "match on flow_cookie": Whether the flow_mod acts only on flows
+ whose flow_cookie matches an optional controller-specified value
+ and mask.
+
+ - "updates flow_cookie": Whether the flow_mod changes the
+ flow_cookie of the flow or flows that it matches to the
+ flow_cookie included in the flow_mod message.
+
+ - "updates OFPFF_ flags": Whether the flow_mod changes the
+ OFPFF_SEND_FLOW_REM flag of the flow or flows that it matches to
+ the setting included in the flags of the flow_mod message.
+
+ - "honors OFPFF_CHECK_OVERLAP": Whether the OFPFF_CHECK_OVERLAP
+ flag in the flow_mod is significant.
+
+ - "updates idle_timeout" and "updates hard_timeout": Whether the
+ idle_timeout and hard_timeout in the flow_mod, respectively,
+ have an effect on the flow or flows matched by the flow_mod.
+
+ - "updates idle timer": Whether the flow_mod resets the per-flow
+ timer that measures how long a flow has been idle.
+
+ - "updates hard timer": Whether the flow_mod resets the per-flow
+ timer that measures how long it has been since a flow was
+ modified.
+
+ - "zeros counters": Whether the flow_mod resets per-flow packet
+ and byte counters to zero.
+
+ - "may add a new flow": Whether the flow_mod may add a new flow to
+ the flow table. (Obviously this is always true for "add"
+ commands but in some OpenFlow versions "modify" and
+ "modify-strict" can also add new flows.)
+
+ - "sends flow_removed message": Whether the flow_mod generates a
+ flow_removed message for the flow or flows that it affects.
+
+An entry labeled "yes" means that the flow mod type does have the
+indicated behavior, "---" means that it does not, an empty cell means
+that the property is not applicable, and other values are explained
+below the table.
+
+OpenFlow 1.0
+------------
+
+ MODIFY DELETE
+ ADD MODIFY STRICT DELETE STRICT
+ === ====== ====== ====== ======
+match on priority yes --- yes --- yes
+match on out_port --- --- --- yes yes
+match on flow_cookie --- --- --- --- ---
+match on table_id --- --- --- --- ---
+controller chooses table_id --- --- ---
+updates flow_cookie yes yes yes
+updates OFPFF_SEND_FLOW_REM yes + +
+honors OFPFF_CHECK_OVERLAP yes + +
+updates idle_timeout yes + +
+updates hard_timeout yes + +
+resets idle timer yes + +
+resets hard timer yes yes yes
+zeros counters yes + +
+may add a new flow yes yes yes
+sends flow_removed message --- --- --- % %
+
+(+) "modify" and "modify-strict" only take these actions when they
+ create a new flow, not when they update an existing flow.
+
+(%) "delete" and "delete_strict" generates a flow_removed message if
+ the deleted flow or flows have the OFPFF_SEND_FLOW_REM flag set.
+ (Each controller can separately control whether it wants to
+ receive the generated messages.)
+
+OpenFlow 1.1
+------------
+
+OpenFlow 1.1 makes these changes:
+
+ - The controller now must specify the table_id of the flow match
+ searched and into which a flow may be inserted. Behavior for a
+ table_id of 255 is undefined.
+
+ - A flow_mod, except an "add", can now match on the flow_cookie.
+
+ - When a flow_mod matches on the flow_cookie, "modify" and
+ "modify-strict" never insert a new flow.
+
+ MODIFY DELETE
+ ADD MODIFY STRICT DELETE STRICT
+ === ====== ====== ====== ======
+match on priority yes --- yes --- yes
+match on out_port --- --- --- yes yes
+match on flow_cookie --- yes yes yes yes
+match on table_id yes yes yes yes yes
+controller chooses table_id yes yes yes
+updates flow_cookie yes --- ---
+updates OFPFF_SEND_FLOW_REM yes + +
+honors OFPFF_CHECK_OVERLAP yes + +
+updates idle_timeout yes + +
+updates hard_timeout yes + +
+resets idle timer yes + +
+resets hard timer yes yes yes
+zeros counters yes + +
+may add a new flow yes # #
+sends flow_removed message --- --- --- % %
+
+(+) "modify" and "modify-strict" only take these actions when they
+ create a new flow, not when they update an existing flow.
+
+(%) "delete" and "delete_strict" generates a flow_removed message if
+ the deleted flow or flows have the OFPFF_SEND_FLOW_REM flag set.
+ (Each controller can separately control whether it wants to
+ receive the generated messages.)
+
+(#) "modify" and "modify-strict" only add a new flow if the flow_mod
+ does not match on any bits of the flow cookie
+
+OpenFlow 1.2
+------------
+
+OpenFlow 1.2 makes these changes:
+
+ - Only "add" commands ever add flows, "modify" and "modify-strict"
+ never do.
+
+ - A new flag OFPFF_RESET_COUNTS now controls whether "modify" and
+ "modify-strict" reset counters, whereas previously they never
+ reset counters (except when they inserted a new flow).
+
+ MODIFY DELETE
+ ADD MODIFY STRICT DELETE STRICT
+ === ====== ====== ====== ======
+match on priority yes --- yes --- yes
+match on out_port --- --- --- yes yes
+match on flow_cookie --- yes yes yes yes
+match on table_id yes yes yes yes yes
+controller chooses table_id yes yes yes
+updates flow_cookie yes --- ---
+updates OFPFF_SEND_FLOW_REM yes --- ---
+honors OFPFF_CHECK_OVERLAP yes --- ---
+updates idle_timeout yes --- ---
+updates hard_timeout yes --- ---
+resets idle timer yes --- ---
+resets hard timer yes yes yes
+zeros counters yes & &
+may add a new flow yes --- ---
+sends flow_removed message --- --- --- % %
+
+(%) "delete" and "delete_strict" generates a flow_removed message if
+ the deleted flow or flows have the OFPFF_SEND_FLOW_REM flag set.
+ (Each controller can separately control whether it wants to
+ receive the generated messages.)
+
+(&) "modify" and "modify-strict" reset counters if the
+ OFPFF_RESET_COUNTS flag is specified.
+
+OpenFlow 1.3
+------------
+
+OpenFlow 1.3 makes these changes:
+
+ - Behavior for a table_id of 255 is now defined, for "delete" and
+ "delete-strict" commands, as meaning to delete from all tables.
+ A table_id of 255 is now explicitly invalid for other commands.
+
+ - New flags OFPFF_NO_PKT_COUNTS and OFPFF_NO_BYT_COUNTS for "add"
+ operations.
+
+The table for 1.3 is the same as the one shown above for 1.2.
+
+
+OFPT_PACKET_IN
+==============
+
+The OpenFlow 1.1 specification for OFPT_PACKET_IN is confusing. The
+definition in OF1.1 openflow.h is[*]:
+
+ /* Packet received on port (datapath -> controller). */
+ struct ofp_packet_in {
+ struct ofp_header header;
+ uint32_t buffer_id; /* ID assigned by datapath. */
+ uint32_t in_port; /* Port on which frame was received. */
+ uint32_t in_phy_port; /* Physical Port on which frame was received. */
+ uint16_t total_len; /* Full length of frame. */
+ uint8_t reason; /* Reason packet is being sent (one of OFPR_*) */
+ uint8_t table_id; /* ID of the table that was looked up */
+ uint8_t data[0]; /* Ethernet frame, halfway through 32-bit word,
+ so the IP header is 32-bit aligned. The
+ amount of data is inferred from the length
+ field in the header. Because of padding,
+ offsetof(struct ofp_packet_in, data) ==
+ sizeof(struct ofp_packet_in) - 2. */
+ };
+ OFP_ASSERT(sizeof(struct ofp_packet_in) == 24);
+
+The confusing part is the comment on the data[] member. This comment
+is a leftover from OF1.0 openflow.h, in which the comment was correct:
+sizeof(struct ofp_packet_in) is 20 in OF1.0 and offsetof(struct
+ofp_packet_in, data) is 18. When OF1.1 was written, the structure
+members were changed but the comment was carelessly not updated, and
+the comment became wrong: sizeof(struct ofp_packet_in) and
+offsetof(struct ofp_packet_in, data) are both 24 in OF1.1.
+
+That leaves the question of how to implement ofp_packet_in in OF1.1.
+The OpenFlow reference implementation for OF1.1 does not include any
+padding, that is, the first byte of the encapsulated frame immediately
+follows the 'table_id' member without a gap. Open vSwitch therefore
+implements it the same way for compatibility.
+
+For an earlier discussion, please see the thread archived at:
+https://mailman.stanford.edu/pipermail/openflow-discuss/2011-August/002604.html
+
+[*] The quoted definition is directly from OF1.1. Definitions used
+ inside OVS omit the 8-byte ofp_header members, so the sizes in
+ this discussion are 8 bytes larger than those declared in OVS
+ header files.
+
+
+VLAN Matching
+=============
+
+The 802.1Q VLAN header causes more trouble than any other 4 bytes in
+networking. More specifically, three versions of OpenFlow and Open
+vSwitch have among them four different ways to match the contents and
+presence of the VLAN header. The following table describes how each
+version works.
+
+ Match NXM OF1.0 OF1.1 OF1.2
+ ----- --------- ----------- ----------- ------------
+ [1] 0000/0000 ????/1,??/? ????/1,??/? 0000/0000,--
+ [2] 0000/ffff ffff/0,??/? ffff/0,??/? 0000/ffff,--
+ [3] 1xxx/1fff 0xxx/0,??/1 0xxx/0,??/1 1xxx/ffff,--
+ [4] z000/f000 ????/1,0y/0 fffe/0,0y/0 1000/1000,0y
+ [5] zxxx/ffff 0xxx/0,0y/0 0xxx/0,0y/0 1xxx/ffff,0y
+ [6] 0000/0fff <none> <none> <none>
+ [7] 0000/f000 <none> <none> <none>
+ [8] 0000/efff <none> <none> <none>
+ [9] 1001/1001 <none> <none> 1001/1001,--
+ [10] 3000/3000 <none> <none> <none>
+
+Each column is interpreted as follows.
+
+ - Match: See the list below.
+
+ - NXM: xxxx/yyyy means NXM_OF_VLAN_TCI_W with value xxxx and mask
+ yyyy. A mask of 0000 is equivalent to omitting
+ NXM_OF_VLAN_TCI(_W), a mask of ffff is equivalent to
+ NXM_OF_VLAN_TCI.
+
+ - OF1.0 and OF1.1: wwww/x,yy/z means dl_vlan wwww, OFPFW_DL_VLAN
+ x, dl_vlan_pcp yy, and OFPFW_DL_VLAN_PCP z. ? means that the
+ given nibble is ignored (and conventionally 0 for wwww or yy,
+ conventionally 1 for x or z). <none> means that the given match
+ is not supported.
+
+ - OF1.2: xxxx/yyyy,zz means OXM_OF_VLAN_VID_W with value xxxx and
+ mask yyyy, and OXM_OF_VLAN_PCP (which is not maskable) with
+ value zz. A mask of 0000 is equivalent to omitting
+ OXM_OF_VLAN_VID(_W), a mask of ffff is equivalent to
+ OXM_OF_VLAN_VID. -- means that OXM_OF_VLAN_PCP is omitted.
+ <none> means that the given match is not supported.
+
+The matches are:
+
+ [1] Matches any packet, that is, one without an 802.1Q header or with
+ an 802.1Q header with any TCI value.
+
+ [2] Matches only packets without an 802.1Q header.
+
+ NXM: Any match with (vlan_tci == 0) and (vlan_tci_mask & 0x1000)
+ != 0 is equivalent to the one listed in the table.
+
+ OF1.0: The spec doesn't define behavior if dl_vlan is set to
+ 0xffff and OFPFW_DL_VLAN_PCP is not set.
+
+ OF1.1: The spec says explicitly to ignore dl_vlan_pcp when
+ dl_vlan is set to 0xffff.
+
+ OF1.2: The spec doesn't say what should happen if (vlan_vid == 0)
+ and (vlan_vid_mask & 0x1000) != 0 but (vlan_vid_mask != 0x1000),
+ but it would be straightforward to also interpret as [2].
+
+ [3] Matches only packets that have an 802.1Q header with VID xxx (and
+ any PCP).
+
+ [4] Matches only packets that have an 802.1Q header with PCP y (and
+ any VID).
+
+ NXM: z is ((y << 1) | 1).
+
+ OF1.0: The spec isn't very clear, but OVS implements it this way.
+
+ OF1.2: Presumably other masks such that (vlan_vid_mask & 0x1fff)
+ == 0x1000 would also work, but the spec doesn't define their
+ behavior.
+
+ [5] Matches only packets that have an 802.1Q header with VID xxx and
+ PCP y.
+
+ NXM: z is ((y << 1) | 1).
+
+ OF1.2: Presumably other masks such that (vlan_vid_mask & 0x1fff)
+ == 0x1fff would also work.
+
+ [6] Matches packets with no 802.1Q header or with an 802.1Q header
+ with a VID of 0. Only possible with NXM.
+
+ [7] Matches packets with no 802.1Q header or with an 802.1Q header
+ with a PCP of 0. Only possible with NXM.
+
+ [8] Matches packets with no 802.1Q header or with an 802.1Q header
+ with both VID and PCP of 0. Only possible with NXM.
+
+ [9] Matches only packets that have an 802.1Q header with an
+ odd-numbered VID (and any PCP). Only possible with NXM and
+ OF1.2. (This is just an example; one can match on any desired
+ VID bit pattern.)
+
+[10] Matches only packets that have an 802.1Q header with an
+ odd-numbered PCP (and any VID). Only possible with NXM. (This
+ is just an example; one can match on any desired VID bit
+ pattern.)
+
+Additional notes:
+
+ - OF1.2: The top three bits of OXM_OF_VLAN_VID are fixed to zero,
+ so bits 13, 14, and 15 in the masks listed in the table may be
+ set to arbitrary values, as long as the corresponding value bits
+ are also zero. The suggested ffff mask for [2], [3], and [5]
+ allows a shorter OXM representation (the mask is omitted) than
+ the minimal 1fff mask.
+
+
+Flow Cookies
+============
+
+OpenFlow 1.0 and later versions have the concept of a "flow cookie",
+which is a 64-bit integer value attached to each flow. The treatment
+of the flow cookie has varied greatly across OpenFlow versions,
+however.
+
+In OpenFlow 1.0:
+
+ - OFPFC_ADD set the cookie in the flow that it added.
+
+ - OFPFC_MODIFY and OFPFC_MODIFY_STRICT updated the cookie for
+ the flow or flows that it modified.
+
+ - OFPST_FLOW messages included the flow cookie.
+
+ - OFPT_FLOW_REMOVED messages reported the cookie of the flow
+ that was removed.
+
+OpenFlow 1.1 made the following changes:
+
+ - Flow mod operations OFPFC_MODIFY, OFPFC_MODIFY_STRICT,
+ OFPFC_DELETE, and OFPFC_DELETE_STRICT, plus flow stats
+ requests and aggregate stats requests, gained the ability to
+ match on flow cookies with an arbitrary mask.
+
+ - OFPFC_MODIFY and OFPFC_MODIFY_STRICT were changed to add a
+ new flow, in the case of no match, only if the flow table
+ modification operation did not match on the cookie field.
+ (In OpenFlow 1.0, modify operations always added a new flow
+ when there was no match.)
+
+ - OFPFC_MODIFY and OFPFC_MODIFY_STRICT no longer updated flow
+ cookies.
+
+OpenFlow 1.2 made the following changes:
+
+ - OFPC_MODIFY and OFPFC_MODIFY_STRICT were changed to never
+ add a new flow, regardless of whether the flow cookie was
+ used for matching.
+
+Open vSwitch support for OpenFlow 1.0 implements the OpenFlow 1.0
+behavior with the following extensions:
+
+ - An NXM extension field NXM_NX_COOKIE(_W) allows the NXM
+ versions of OFPFC_MODIFY, OFPFC_MODIFY_STRICT, OFPFC_DELETE,
+ and OFPFC_DELETE_STRICT flow_mods, plus flow stats requests
+ and aggregate stats requests, to match on flow cookies with
+ arbitrary masks. This is much like the equivalent OpenFlow
+ 1.1 feature.
+
+ - Like OpenFlow 1.1, OFPC_MODIFY and OFPFC_MODIFY_STRICT add a
+ new flow if there is no match and the mask is zero (or not
+ given).
+
+ - The "cookie" field in OFPT_FLOW_MOD and NXT_FLOW_MOD messages
+ is used as the cookie value for OFPFC_ADD commands, as
+ described in OpenFlow 1.0. For OFPFC_MODIFY and
+ OFPFC_MODIFY_STRICT commands, the "cookie" field is used as a
+ new cookie for flows that match unless it is UINT64_MAX, in
+ which case the flow's cookie is not updated.
+
+ - NXT_PACKET_IN (the Nicira extended version of
+ OFPT_PACKET_IN) reports the cookie of the rule that
+ generated the packet, or all-1-bits if no rule generated the
+ packet. (Older versions of OVS used all-0-bits instead of
+ all-1-bits.)
+
+The following table shows the handling of different protocols when
+receiving OFPFC_MODIFY and OFPFC_MODIFY_STRICT messages. A mask of 0
+indicates either an explicit mask of zero or an implicit one by not
+specifying the NXM_NX_COOKIE(_W) field.
+
+ Match Update Add on miss Add on miss
+ cookie cookie mask!=0 mask==0
+ ====== ====== =========== ===========
+OpenFlow 1.0 no yes <always add on miss>
+OpenFlow 1.1 yes no no yes
+OpenFlow 1.2 yes no no no
+NXM yes yes* no yes
+
+* Updates the flow's cookie unless the "cookie" field is UINT64_MAX.
+
+
+Multiple Table Support
+======================
+
+OpenFlow 1.0 has only rudimentary support for multiple flow tables.
+Notably, OpenFlow 1.0 does not allow the controller to specify the
+flow table to which a flow is to be added. Open vSwitch adds an
+extension for this purpose, which is enabled on a per-OpenFlow
+connection basis using the NXT_FLOW_MOD_TABLE_ID message. When the
+extension is enabled, the upper 8 bits of the 'command' member in an
+OFPT_FLOW_MOD or NXT_FLOW_MOD message designates the table to which a
+flow is to be added.
+
+The Open vSwitch software switch implementation offers 255 flow
+tables. On packet ingress, only the first flow table (table 0) is
+searched, and the contents of the remaining tables are not considered
+in any way. Tables other than table 0 only come into play when an
+NXAST_RESUBMIT_TABLE action specifies another table to search.
+
+Tables 128 and above are reserved for use by the switch itself.
+Controllers should use only tables 0 through 127.
+