environments: OpenFlow, which exposes flow-based forwarding state,
and the OVSDB management protocol, which exposes switch port state.
In addition to the switch implementation itself, Open vSwitch
- includes tools (ovs-controller, ovs-ofctl, ovs-vsctl) that developers
- can script and extend to provide distributed vswitch capabilities
- that are closely integrated with their virtualization management
- platform.
+ includes tools (ovs-ofctl, ovs-vsctl) that developers can script and
+ extend to provide distributed vswitch capabilities that are closely
+ integrated with their virtualization management platform.
Q: Why doesn't Open vSwitch support distribution?
kernel version included in the same release or with the version
from upstream Linux. However, when upgrading between two releases
of Open vSwitch it is best to migrate userspace first to reduce
- the possbility of incompatibilities.
+ the possibility of incompatibilities.
Q: What features are not available in the Open vSwitch kernel datapath
that ships as part of the upstream Linux kernel?
ports will not work with the userspace datapath, only with the
kernel module.
-Q: Why are there so many different ways to dump flows?
+
+Implementation Details
+----------------------
+
+Q: I hear OVS has a couple of kinds of flows. Can you tell me about them?
A: Open vSwitch uses different kinds of flows for different purposes:
about hidden flows.)
- The Open vSwitch software switch implementation uses a second
- kind of flow internally. These flows, called "exact-match"
- or "datapath" or "kernel" flows, do not support wildcards or
- priorities and comprise only a single table, which makes them
- suitable for caching. OpenFlow flows and exact-match flows
+ kind of flow internally. These flows, called "datapath" or
+ "kernel" flows, do not support priorities and comprise only a
+ single table, which makes them suitable for caching. (Like
+ OpenFlow flows, datapath flows do support wildcarding, in Open
+ vSwitch 1.11 and later.) OpenFlow flows and datapath flows
also support different actions and number ports differently.
- Exact-match flows are an implementation detail that is
- subject to change in future versions of Open vSwitch. Even
- with the current version of Open vSwitch, hardware switch
- implementations do not necessarily use exact-match flows.
+ Datapath flows are an implementation detail that is subject to
+ change in future versions of Open vSwitch. Even with the
+ current version of Open vSwitch, hardware switch
+ implementations do not necessarily use this architecture.
- Each of the commands for dumping flows has a different purpose:
+ Users and controllers directly control only the OpenFlow flow
+ table. Open vSwitch manages the datapath flow table itself, so
+ users should not normally be concerned with it.
+
+Q: Why are there so many different ways to dump flows?
+
+A: Open vSwitch has two kinds of flows (see the previous question), so
+ it has commands with different purposes for dumping each kind of
+ flow:
- "ovs-ofctl dump-flows <br>" dumps OpenFlow flows, excluding
hidden flows. This is the most commonly useful form of flow
including hidden flows. This is occasionally useful for
troubleshooting suspected issues with in-band control.
- - "ovs-dpctl dump-flows [dp]" dumps the exact-match flow table
+ - "ovs-dpctl dump-flows [dp]" dumps the datapath flow table
entries for a Linux kernel-based datapath. In Open vSwitch
1.10 and later, ovs-vswitchd merges multiple switches into a
single datapath, so it will show all the flows on all your
useful for debugging.
- "ovs-appctl dpif/dump-flows <br>", new in Open vSwitch 1.10,
- dumps exact-match flows for only the specified bridge,
- regardless of the type.
+ dumps datapath flows for only the specified bridge, regardless
+ of the type.
+
+
+Performance
+-----------
+
+Q: I just upgraded and I see a performance drop. Why?
+
+A: The OVS kernel datapath may have been updated to a newer version than
+ the OVS userspace components. Sometimes new versions of OVS kernel
+ module add functionality that is backwards compatible with older
+ userspace components but may cause a drop in performance with them.
+ Especially, if a kernel module from OVS 2.1 or newer is paired with
+ OVS userspace 1.10 or older, there will be a performance drop for
+ TCP traffic.
+
+ Updating the OVS userspace components to the latest released
+ version should fix the performance degradation.
+
+ To get the best possible performance and functionality, it is
+ recommended to pair the same versions of the kernel module and OVS
+ userspace.
Configuration Problems
Q: How do I make a flow drop packets?
-A: An empty set of actions causes a packet to be dropped. You can
- specify an empty set of actions with "actions=" on the ovs-ofctl
- command line. For example:
+A: To drop a packet is to receive it without forwarding it. OpenFlow
+ explicitly specifies forwarding actions. Thus, a flow with an
+ empty set of actions does not forward packets anywhere, causing
+ them to be dropped. You can specify an empty set of actions with
+ "actions=" on the ovs-ofctl command line. For example:
ovs-ofctl add-flow br0 priority=65535,actions=
ovs-ofctl add-flow br0 priority=65535,actions=drop
+ "drop" is not an action, either in OpenFlow or Open vSwitch.
+ Rather, it is only a way to say that there are no actions.
+
Q: I added a flow to send packets out the ingress port, like this:
ovs-ofctl add-flow br0 in_port=2,actions=2
git://git.onelab.eu / sliver-openvswitch.git / blobdiff