section describes how all of these features interact.
First, a service controller never receives any asynchronous messages
-unless it explicitly configures a miss_send_len greater than zero with
-an OFPT_SET_CONFIG message.
+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
receive the generated messages.)
+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 z,
+ 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
============
gateway.
+Action Reproduction
+===================
+
+It seems likely that many controllers, at least at startup, use the
+OpenFlow "flow statistics" request to obtain existing flows, then
+compare the flows' actions against the actions that they expect to
+find. Before version 1.8.0, Open vSwitch always returned exact,
+byte-for-byte copies of the actions that had been added to the flow
+table. The current version of Open vSwitch does not always do this in
+some exceptional cases. This section lists the exceptions that
+controller authors must keep in mind if they compare actual actions
+against desired actions in a bytewise fashion:
+
+ - Open vSwitch zeros padding bytes in action structures,
+ regardless of their values when the flows were added.
+
+ - Open vSwitch "normalizes" the instructions in OpenFlow 1.1
+ (and later) in the following way:
+
+ * OVS sorts the instructions into the following order:
+ Apply-Actions, Clear-Actions, Write-Actions,
+ Write-Metadata, Goto-Table.
+
+ * OVS drops Apply-Actions instructions that have empty
+ action lists.
+
+ * OVS drops Write-Actions instructions that have empty
+ action sets.
+
+Please report other discrepancies, if you notice any, so that we can
+fix or document them.
+
+
Suggestions
===========