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I wrote most of this myself.  The answer to "I can't seem to use Open
vSwitch in a wireless network" is based on a response by Jesse Gross:
http://openvswitch.org/pipermail/discuss/2011-January/004707.html

Signed-off-by: Ben Pfaff <blp@nicira.com>
This commit is contained in:
Ben Pfaff 2012-06-12 09:40:11 -07:00
parent b5600ca2d0
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7 changed files with 330 additions and 1 deletions
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FAQ Normal file
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Open vSwitch <http://openvswitch.org>
Frequently Asked Questions
==========================
Configuration Problems
----------------------
Q: I created a bridge and added my Ethernet port to it, using commands
like these:
ovs-vsctl add-br br0
ovs-vsctl add-port br0 eth0
and as soon as I ran the "add-port" command I lost all connectivity
through eth0. Help!
A: A physical Ethernet device that is part of an Open vSwitch bridge
should not have an IP address. If one does, then that IP address
will not be fully functional.
You can restore functionality by moving the IP address to an Open
vSwitch "internal" device, such as the network device named after
the bridge itself. For example, assuming that eth0's IP address is
192.168.128.5, you could run the commands below to fix up the
situation:
ifconfig eth0 0.0.0.0
ifconfig br0 192.168.128.5
(If your only connection to the machine running OVS is through the
IP address in question, then you would want to run all of these
commands on a single command line, or put them into a script.) If
there were any additional routes assigned to eth0, then you would
also want to use commands to adjust these routes to go through br0.
If you use DHCP to obtain an IP address, then you should kill the
DHCP client that was listening on the physical Ethernet interface
(e.g. eth0) and start one listening on the internal interface
(e.g. br0). You might still need to manually clear the IP address
from the physical interface (e.g. with "ifconfig eth0 0.0.0.0").
There is no compelling reason why Open vSwitch must work this way.
However, this is the way that the Linux kernel bridge module has
always worked, so it's a model that those accustomed to Linux
bridging are already used to. Also, the model that most people
expect is not implementable without kernel changes on all the
versions of Linux that Open vSwitch supports.
By the way, this issue is not specific to physical Ethernet
devices. It applies to all network devices except Open vswitch
"internal" devices.
Q: I created a bridge and added a couple of Ethernet ports to it,
using commands like these:
ovs-vsctl add-br br0
ovs-vsctl add-port br0 eth0
ovs-vsctl add-port br0 eth1
and now my network seems to have melted: connectivity is unreliable
(even connectivity that doesn't go through Open vSwitch), all the
LEDs on my physical switches are blinking, and wireshark shows
duplicated packets.
A: More than likely, you've looped your network. Probably, eth0 and
eth1 are connected to the same physical Ethernet switch. This
yields a scenario where OVS receives a broadcast packet on eth0 and
sends it out on eth1, then the physical switch connected to eth1
sends the packet back on eth0, and so on forever. More complicated
scenarios, involving a loop through multiple switches, are possible
too.
The solution depends on what you are trying to do:
- If you added eth0 and eth1 to get higher bandwidth or higher
reliability between OVS and your physical Ethernet switch,
use a bond. The following commands create br0 and then add
eth0 and eth1 as a bond:
ovs-vsctl add-br br0
ovs-vsctl add-bond br0 bond0 eth0 eth1
Bonds have tons of configuration options. Please read the
documentation on the Port table in ovs-vswitchd.conf.db(5)
for all the details.
- Perhaps you don't actually need eth0 and eth1 to be on the
same bridge. For example, if you simply want to be able to
connect each of them to virtual machines, then you can put
each of them on a bridge of its own:
ovs-vsctl add-br br0
ovs-vsctl add-port br0 eth0
ovs-vsctl add-br br1
ovs-vsctl add-port br1 eth1
and then connect VMs to br0 and br1. (A potential
disadvantage is that traffic cannot directly pass between br0
and br1. Instead, it will go out eth0 and come back in eth1,
or vice versa.)
- If you have a redundant or complex network topology and you
want to prevent loops, turn on spanning tree protocol (STP).
The following commands create br0, enable STP, and add eth0
and eth1 to the bridge. The order is important because you
don't want have to have a loop in your network even
transiently:
ovs-vsctl add-br br0
ovs-vsctl set bridge br0 stp_enable=true
ovs-vsctl add-port br0 eth0
ovs-vsctl add-port br0 eth1
The Open vSwitch implementation of STP is not well tested.
Please report any bugs you observe, but if you'd rather avoid
acting as a beta tester then another option might be your
best shot.
Q: I can't seem to use Open vSwitch in a wireless network.
A: Wireless base stations generally only allow packets with the source
MAC address of NIC that completed the initial handshake.
Therefore, without MAC rewriting, only a single device can
communicate over a single wireless link.
This isn't specific to Open vSwitch, it's enforced by the access
point, so the same problems will show up with the Linux bridge or
any other way to do bridging.
VLANs
-----
Q: VLANs don't work.
A: Many drivers in Linux kernels before version 3.3 had VLAN-related
bugs. If you are having problems with VLANs that you suspect to be
driver related, then you have several options:
- Upgrade to Linux 3.3 or later.
- Build and install a fixed version of the particular driver
that is causing trouble, if one is available.
- Use a NIC whose driver does not have VLAN problems.
- Use "VLAN splinters", a feature in Open vSwitch 1.4 and later
that works around bugs in kernel drivers. To enable VLAN
splinters on interface eth0, use the command:
ovs-vsctl set interface eth0 other-config:enable-vlan-splinters=true
For VLAN splinters to be effective, Open vSwitch must know
which VLANs are in use. See the "VLAN splinters" section in
the Interface table in ovs-vswitchd.conf.db(5) for details on
how Open vSwitch infers in-use VLANs.
VLAN splinters increase memory use and reduce performance, so
use them only if needed.
- Apply the "vlan workaround" patch from the XenServer kernel
patch queue, build Open vSwitch against this patched kernel,
and then use ovs-vlan-bug-workaround(8) to enable the VLAN
workaround for each interface whose driver is buggy.
(This is a nontrivial exercise, so this option is included
only for completeness.)
It is not always easy to tell whether a Linux kernel driver has
buggy VLAN support. The ovs-vlan-test(8) and ovs-test(8) utilities
can help you test. See their manpages for details. Of the two
utilities, ovs-test(8) is newer and more thorough, but
ovs-vlan-test(8) may be easier to use.
Q: VLANs still don't work. I've tested the driver so I know that it's OK.
A: Do you have VLANs enabled on the physical switch that OVS is
attached to? Make sure that the port is configured to trunk the
VLAN or VLANs that you are using with OVS.
Q: Outgoing VLAN-tagged traffic goes through OVS to my physical switch
and to its destination host, but OVS seems to drop incoming return
traffic.
A: It's possible that you have the VLAN configured on your physical
switch as the "native" VLAN. In this mode, the switch treats
incoming packets either tagged with the native VLAN or untagged as
part of the native VLAN. It may also send outgoing packets in the
native VLAN without a VLAN tag.
If this is the case, you have two choices:
- Change the physical switch port configuration to tag packets
it forwards to OVS with the native VLAN instead of forwarding
them untagged.
- Change the OVS configuration for the physical port to a
native VLAN mode. For example, the following sets up a
bridge with port eth0 in "native-tagged" mode in VLAN 9:
ovs-vsctl add-br br0
ovs-vsctl add-port br0 eth0 tag=9 vlan_mode=native-tagged
In this situation, "native-untagged" mode will probably work
equally well. Refer to the documentation for the Port table
in ovs-vswitchd.conf.db(5) for more information.
Q: Can I configure an IP address on a VLAN?
A: Yes. Use an "internal port" configured as an access port. For
example, the following configures IP address 192.168.0.7 on VLAN 9.
That is, OVS will forward packets from eth0 to 192.168.0.7 only if
they have an 802.1Q header with VLAN 9. Conversely, traffic
forwarded from 192.168.0.7 to eth0 will be tagged with an 802.1Q
header with VLAN 9:
ovs-vsctl add-br br0
ovs-vsctl add-port br0 eth0
ovs-vsctl add-port br0 vlan9 tag=9 -- set interface vlan9 type=internal
ifconfig vlan9 192.168.0.7
Q: My OpenFlow controller doesn't see the VLANs that I expect.
A: The configuration for VLANs in the Open vSwitch database (e.g. via
ovs-vsctl) only affects traffic that goes through Open vSwitch's
implementation of the OpenFlow "normal switching" action. By
default, when Open vSwitch isn't connected to a controller and
nothing has been manually configured in the flow table, all traffic
goes through the "normal switching" action. But, if you set up
OpenFlow flows on your own, through a controller or using ovs-ofctl
or through other means, then you have to implement VLAN handling
yourself.
You can use "normal switching" as a component of your OpenFlow
actions, e.g. by putting "normal" into the lists of actions on
ovs-ofctl or by outputting to OFPP_NORMAL from an OpenFlow
controller. This will only be suitable for some situations,
though.
Controllers
-----------
Q: I'm getting "error type 45250 code 0". What's that?
A: This is a Open vSwitch extension to OpenFlow error codes. Open
vSwitch uses this extension when it must report an error to an
OpenFlow controller but no standard OpenFlow error code is
suitable.
Open vSwitch logs the errors that it sends to controllers, so the
easiest thing to do is probably to look at the ovs-vswitchd log to
find out what the error was.
If you want to dissect the extended error message yourself, the
format is documented in include/openflow/nicira-ext.h in the Open
vSwitch source distribution. The extended error codes are
documented in lib/ofp-errors.h.
Q1: Some of the traffic that I'd expect my OpenFlow controller to see
doesn't actually appear through the OpenFlow connection, even
though I know that it's going through.
Q2: Some of the OpenFlow flows that my controller sets up don't seem
to apply to certain traffic, especially traffic between OVS and
the controller itself.
A: By default, Open vSwitch assumes that OpenFlow controllers are
connected "in-band", that is, that the controllers are actually
part of the network that is being controlled. In in-band mode,
Open vSwitch sets up special "hidden" flows to make sure that
traffic can make it back and forth between OVS and the controllers.
These hidden flows are higher priority than any flows that can be
set up through OpenFlow, and they are not visible through normal
OpenFlow flow table dumps.
Usually, the hidden flows are desirable and helpful, but
occasionally they can cause unexpected behavior. You can view the
full OpenFlow flow table, including hidden flows, on bridge br0
with the command:
ovs-appctl bridge/dump-flows br0
to help you debug. The hidden flows are those with priorities
greater than 65535 (the maximum priority that can be set with
OpenFlow).
The DESIGN file at the top level of the Open vSwitch source
distribution describes the in-band model in detail.
If your controllers are not actually in-band (e.g. they are on
localhost via 127.0.0.1, or on a separate network), then you should
configure your controllers in "out-of-band" mode. If you have one
controller on bridge br0, then you can configure out-of-band mode
on it with:
ovs-vsctl set controller br0 connection-mode=out-of-band
Q: I configured all my controllers for out-of-band control mode but
"ovs-appctl bridge/dump-flows" still shows some hidden flows.
A: You probably have a remote manager configured (e.g. with "ovs-vsctl
set-manager"). By default, Open vSwitch assumes that managers need
in-band rules set up on every bridge. You can disable these rules
on bridge br0 with:
ovs-vsctl set bridge br0 other-config:disable-in-band=true
This actually disables in-band control entirely for the bridge, as
if all the bridge's controllers were configured for out-of-band
control.
Q: My OpenFlow controller doesn't see the VLANs that I expect.
A: See answer under "VLANs", above.
Contact
-------
bugs@openvswitch.org
http://openvswitch.org/

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Makefile.am
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@ -41,6 +41,7 @@ PYCOV_CLEAN_FILES = build-aux/check-structs,cover
EXTRA_DIST = \
CodingStyle \
DESIGN \
FAQ \
INSTALL.KVM \
INSTALL.Libvirt \
INSTALL.Linux \

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NEWS
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@ -1,5 +1,6 @@
post-v1.7.0
------------------------
- New FAQ. Please send updates and additions!
- ovs-ofctl:
- "mod-port" command can now control all OpenFlow config flags.
- Added support for arbitrary ethernet masks

2
README
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@ -90,6 +90,8 @@ What other documentation is available?
To install Open vSwitch on a regular Linux machine, read INSTALL.Linux.
For answers to common questions, read FAQ.
To use Open vSwitch as a drop-in replacement for the Linux bridge,
read INSTALL.bridge.

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debian/automake.mk vendored
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@ -12,6 +12,7 @@ EXTRA_DIST += \
debian/openvswitch-brcompat.postinst \
debian/openvswitch-brcompat.postrm \
debian/openvswitch-common.dirs \
debian/openvswitch-common.docs \
debian/openvswitch-common.install \
debian/openvswitch-common.manpages \
debian/openvswitch-controller.README.Debian \

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debian/openvswitch-common.docs vendored Normal file
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FAQ

3
rhel/openvswitch.spec.in
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@ -50,7 +50,7 @@ rhel_cp usr_share_openvswitch_scripts_sysconfig.template 0644
docdir=$RPM_BUILD_ROOT/usr/share/doc/openvswitch-%{version}
install -d -m755 "$docdir"
install -m 0644 rhel/README.RHEL "$docdir"
install -m 0644 FAQ rhel/README.RHEL "$docdir"
install python/compat/uuid.py $RPM_BUILD_ROOT/usr/share/openvswitch/python
install python/compat/argparse.py $RPM_BUILD_ROOT/usr/share/openvswitch/python
@ -152,5 +152,6 @@ exit 0
/usr/share/openvswitch/scripts/ovs-save
/usr/share/openvswitch/scripts/sysconfig.template
/usr/share/openvswitch/vswitch.ovsschema
/usr/share/doc/openvswitch-%{version}/FAQ
/usr/share/doc/openvswitch-%{version}/README.RHEL
/var/lib/openvswitch