datapath: genlmsg_new_unicast to genlmsg_new

[cascardo/ovs.git] / FAQ.md

diff --git a/FAQ.md b/FAQ.md
index 9f3dc61..063bd70 100644 (file)
--- a/FAQ.md
+++ b/FAQ.md
@@ -199,6 +199,9 @@ Tunnel - STT          |      NO        |       YES      |    NO     |   YES   |
 Tunnel - GRE          |      3.11      |       YES      |    YES    |   YES   |
 Tunnel - VXLAN        |      3.12      |       YES      |    YES    |   YES   |
 Tunnel - Geneve       |      3.18      |       YES      |    YES    |   YES   |
+Tunnel - GRE-IPv6     |      NO        |       NO       |    YES    |   NO    |
+Tunnel - VXLAN-IPv6   |      4.3       |       YES      |    YES    |   NO    |
+Tunnel - Geneve-IPv6  |      4.4       |       YES      |    YES    |   NO    |
 QoS - Policing        |      YES       |       YES      |    NO     |   NO    |
 QoS - Shaping         |      YES       |       YES      |    NO     |   NO    |
 sFlow                 |      YES       |       YES      |    YES    |   NO    |
@@ -2029,6 +2032,47 @@ A: OpenFlow actions are executed in the order specified.  Thus, the
 
        ovs-ofctl add-flow br0 dl_vlan=123,actions=mod_vlan_vid:456,output:1
 
+### Q: The "learn" action can't learn the action I want, can you improve it?
+
+A: 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:
+       http://openvswitch.org/pipermail/discuss/2016-June/021694.html
+
+     - MAC learning in the middle of a pipeline, as described in
+       [Tutorial.md].
+
+     - TCP state based firewalling, by learning outgoing connections
+       based on SYN packets and matching them up with incoming
+       packets.
+
+     - At least some of the features described in T. A. Hoff,
+       "Extending Open vSwitch to Facilitate Creation of Stateful SDN
+       Applications".
+
 
 Development
 -----------
@@ -2095,3 +2139,4 @@ http://openvswitch.org/
 [INSTALL.md]:INSTALL.md
 [OPENFLOW-1.1+.md]:OPENFLOW-1.1+.md
 [INSTALL.DPDK.md]:INSTALL.DPDK.md
+[Tutorial.md]:tutorial/Tutorial.md