X-Git-Url: http://git.onelab.eu/?p=sliver-openvswitch.git;a=blobdiff_plain;f=FAQ;h=c43b0c8f3b3177cc55c30b4a714ebad90e9fd362;hp=678ca2cffc9e306fdf28a4c02f96de8eac338596;hb=c5cf10598f8c9f4428291e9df3ecd72a05fb1ccf;hpb=c483d489caeec8b38991065580365e8a2b34237e diff --git a/FAQ b/FAQ index 678ca2cff..c43b0c8f3 100644 --- a/FAQ +++ b/FAQ @@ -3,6 +3,518 @@ Frequently Asked Questions ========================== +General +------- + +Q: What is Open vSwitch? + +A: Open vSwitch is a production quality open source software switch + designed to be used as a vswitch in virtualized server + environments. A vswitch forwards traffic between different VMs on + the same physical host and also forwards traffic between VMs and + the physical network. Open vSwitch supports standard management + interfaces (e.g. sFlow, NetFlow, IPFIX, RSPAN, CLI), and is open to + programmatic extension and control using OpenFlow and the OVSDB + management protocol. + + Open vSwitch as designed to be compatible with modern switching + chipsets. This means that it can be ported to existing high-fanout + switches allowing the same flexible control of the physical + infrastructure as the virtual infrastructure. It also means that + Open vSwitch will be able to take advantage of on-NIC switching + chipsets as their functionality matures. + +Q: What virtualization platforms can use Open vSwitch? + +A: Open vSwitch can currently run on any Linux-based virtualization + platform (kernel 2.6.32 and newer), including: KVM, VirtualBox, Xen, + Xen Cloud Platform, XenServer. As of Linux 3.3 it is part of the + mainline kernel. The bulk of the code is written in platform- + independent C and is easily ported to other environments. We welcome + inquires about integrating Open vSwitch with other virtualization + platforms. + +Q: How can I try Open vSwitch? + +A: The Open vSwitch source code can be built on a Linux system. You can + build and experiment with Open vSwitch on any Linux machine. + Packages for various Linux distributions are available on many + platforms, including: Debian, Ubuntu, Fedora. + + You may also download and run a virtualization platform that already + has Open vSwitch integrated. For example, download a recent ISO for + XenServer or Xen Cloud Platform. Be aware that the version + integrated with a particular platform may not be the most recent Open + vSwitch release. + +Q: Does Open vSwitch only work on Linux? + +A: No, Open vSwitch has been ported to a number of different operating + systems and hardware platforms. Most of the development work occurs + on Linux, but the code should be portable to any POSIX system. We've + seen Open vSwitch ported to a number of different platforms, + including FreeBSD, Windows, and even non-POSIX embedded systems. + + By definition, the Open vSwitch Linux kernel module only works on + Linux and will provide the highest performance. However, a userspace + datapath is available that should be very portable. + +Q: What's involved with porting Open vSwitch to a new platform or + switching ASIC? + +A: The PORTING document describes how one would go about porting Open + vSwitch to a new operating system or hardware platform. + +Q: Why would I use Open vSwitch instead of the Linux bridge? + +A: Open vSwitch is specially designed to make it easier to manage VM + network configuration and monitor state spread across many physical + hosts in dynamic virtualized environments. Please see WHY-OVS for a + more detailed description of how Open vSwitch relates to the Linux + Bridge. + +Q: How is Open vSwitch related to distributed virtual switches like the + VMware vNetwork distributed switch or the Cisco Nexus 1000V? + +A: Distributed vswitch applications (e.g., VMware vNetwork distributed + switch, Cisco Nexus 1000V) provide a centralized way to configure and + monitor the network state of VMs that are spread across many physical + hosts. Open vSwitch is not a distributed vswitch itself, rather it + runs on each physical host and supports remote management in a way + that makes it easier for developers of virtualization/cloud + management platforms to offer distributed vswitch capabilities. + + To aid in distribution, Open vSwitch provides two open protocols that + are specially designed for remote management in virtualized network + 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-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? + +A: Open vSwitch is intended to be a useful component for building + flexible network infrastructure. There are many different approaches + to distribution which balance trade-offs between simplicity, + scalability, hardware compatibility, convergence times, logical + forwarding model, etc. The goal of Open vSwitch is to be able to + support all as a primitive building block rather than choose a + particular point in the distributed design space. + +Q: How can I contribute to the Open vSwitch Community? + +A: You can start by joining the mailing lists and helping to answer + questions. You can also suggest improvements to documentation. If + you have a feature or bug you would like to work on, send a mail to + one of the mailing lists: + + http://openvswitch.org/mlists/ + + +Releases +-------- + +Q: What does it mean for an Open vSwitch release to be LTS (long-term + support)? + +A: All official releases have been through a comprehensive testing + process and are suitable for production use. Planned releases will + occur several times a year. If a significant bug is identified in an + LTS release, we will provide an updated release that includes the + fix. Releases that are not LTS may not be fixed and may just be + supplanted by the next major release. The current LTS release is + 1.9.x. + +Q: What Linux kernel versions does each Open vSwitch release work with? + +A: The following table lists the Linux kernel versions against which the + given versions of the Open vSwitch kernel module will successfully + build. The Linux kernel versions are upstream kernel versions, so + Linux kernels modified from the upstream sources may not build in + some cases even if they are based on a supported version. This is + most notably true of Red Hat Enterprise Linux (RHEL) kernels, which + are extensively modified from upstream. + + Open vSwitch Linux kernel + ------------ ------------- + 1.4.x 2.6.18 to 3.2 + 1.5.x 2.6.18 to 3.2 + 1.6.x 2.6.18 to 3.2 + 1.7.x 2.6.18 to 3.3 + 1.8.x 2.6.18 to 3.4 + 1.9.x 2.6.18 to 3.8 + 1.10.x 2.6.18 to 3.8 + 1.11.x 2.6.18 to 3.8 + 2.0.x 2.6.32 to 3.10 + 2.1.x 2.6.32 to 3.11 + 2.2.x 2.6.32 to 3.13 + + Open vSwitch userspace should also work with the Linux kernel module + built into Linux 3.3 and later. + + Open vSwitch userspace is not sensitive to the Linux kernel version. + It should build against almost any kernel, certainly against 2.6.32 + and later. + +Q: I get an error like this when I configure Open vSwitch: + + configure: error: Linux kernel in is version , but + version newer than is not supported (please refer to the + FAQ for advice) + + What should I do? + +A: If there is a newer version of Open vSwitch, consider building that + one, because it may support the kernel that you are building + against. (To find out, consult the table in the previous answer.) + + Otherwise, use the Linux kernel module supplied with the kernel + that you are using. All versions of Open vSwitch userspace are + compatible with all versions of the Open vSwitch kernel module, so + this will also work. See also the following question. + +Q: What features are not available in the Open vSwitch kernel datapath + that ships as part of the upstream Linux kernel? + +A: The kernel module in upstream Linux does not include support for + LISP. Work is in progress to add support for LISP to the upstream + Linux version of the Open vSwitch kernel module. For now, if you + need this feature, use the kernel module from the Open vSwitch + distribution instead of the upstream Linux kernel module. + + Certain features require kernel support to function or to have + reasonable performance. If the ovs-vswitchd log file indicates that + a feature is not supported, consider upgrading to a newer upstream + Linux release or using the kernel module paired with the userspace + distribution. + +Q: What features are not available when using the userspace datapath? + +A: Tunnel virtual ports are not supported, as described in the + previous answer. It is also not possible to use queue-related + actions. On Linux kernels before 2.6.39, maximum-sized VLAN packets + may not be transmitted. + +Q: What Linux kernel versions does IPFIX flow monitoring work with? + +A: IPFIX flow monitoring requires the Linux kernel module from Open + vSwitch version 1.10.90 or later. + +Q: Should userspace or kernel be upgraded first to minimize downtime? + + In general, the Open vSwitch userspace should be used with the + 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 possibility of incompatibilities. + +Q: What happened to the bridge compatibility feature? + +A: Bridge compatibility was a feature of Open vSwitch 1.9 and earlier. + When it was enabled, Open vSwitch imitated the interface of the + Linux kernel "bridge" module. This allowed users to drop Open + vSwitch into environments designed to use the Linux kernel bridge + module without adapting the environment to use Open vSwitch. + + Open vSwitch 1.10 and later do not support bridge compatibility. + The feature was dropped because version 1.10 adopted a new internal + architecture that made bridge compatibility difficult to maintain. + Now that many environments use OVS directly, it would be rarely + useful in any case. + + To use bridge compatibility, install OVS 1.9 or earlier, including + the accompanying kernel modules (both the main and bridge + compatibility modules), following the instructions that come with + the release. Be sure to start the ovs-brcompatd daemon. + + +Terminology +----------- + +Q: I thought Open vSwitch was a virtual Ethernet switch, but the + documentation keeps talking about bridges. What's a bridge? + +A: In networking, the terms "bridge" and "switch" are synonyms. Open + vSwitch implements an Ethernet switch, which means that it is also + an Ethernet bridge. + +Q: What's a VLAN? + +A: See the "VLAN" section below. + + +Basic Configuration +------------------- + +Q: How do I configure a port as an access port? + +A: Add "tag=VLAN" to your "ovs-vsctl add-port" command. For example, + the following commands configure br0 with eth0 as a trunk port (the + default) and tap0 as an access port for VLAN 9: + + ovs-vsctl add-br br0 + ovs-vsctl add-port br0 eth0 + ovs-vsctl add-port br0 tap0 tag=9 + + If you want to configure an already added port as an access port, + use "ovs-vsctl set", e.g.: + + ovs-vsctl set port tap0 tag=9 + +Q: How do I configure a port as a SPAN port, that is, enable mirroring + of all traffic to that port? + +A: The following commands configure br0 with eth0 and tap0 as trunk + ports. All traffic coming in or going out on eth0 or tap0 is also + mirrored to tap1; any traffic arriving on tap1 is dropped: + + ovs-vsctl add-br br0 + ovs-vsctl add-port br0 eth0 + ovs-vsctl add-port br0 tap0 + ovs-vsctl add-port br0 tap1 \ + -- --id=@p get port tap1 \ + -- --id=@m create mirror name=m0 select-all=true output-port=@p \ + -- set bridge br0 mirrors=@m + + To later disable mirroring, run: + + ovs-vsctl clear bridge br0 mirrors + +Q: Does Open vSwitch support configuring a port in promiscuous mode? + +A: Yes. How you configure it depends on what you mean by "promiscuous + mode": + + - Conventionally, "promiscuous mode" is a feature of a network + interface card. Ordinarily, a NIC passes to the CPU only the + packets actually destined to its host machine. It discards + the rest to avoid wasting memory and CPU cycles. When + promiscuous mode is enabled, however, it passes every packet + to the CPU. On an old-style shared-media or hub-based + network, this allows the host to spy on all packets on the + network. But in the switched networks that are almost + everywhere these days, promiscuous mode doesn't have much + effect, because few packets not destined to a host are + delivered to the host's NIC. + + This form of promiscuous mode is configured in the guest OS of + the VMs on your bridge, e.g. with "ifconfig". + + - The VMware vSwitch uses a different definition of "promiscuous + mode". When you configure promiscuous mode on a VMware vNIC, + the vSwitch sends a copy of every packet received by the + vSwitch to that vNIC. That has a much bigger effect than just + enabling promiscuous mode in a guest OS. Rather than getting + a few stray packets for which the switch does not yet know the + correct destination, the vNIC gets every packet. The effect + is similar to replacing the vSwitch by a virtual hub. + + This "promiscuous mode" is what switches normally call "port + mirroring" or "SPAN". For information on how to configure + SPAN, see "How do I configure a port as a SPAN port, that is, + enable mirroring of all traffic to that port?" + +Q: How do I configure a VLAN as an RSPAN VLAN, that is, enable + mirroring of all traffic to that VLAN? + +A: The following commands configure br0 with eth0 as a trunk port and + tap0 as an access port for VLAN 10. All traffic coming in or going + out on tap0, as well as traffic coming in or going out on eth0 in + VLAN 10, is also mirrored to VLAN 15 on eth0. The original tag for + VLAN 10, in cases where one is present, is dropped as part of + mirroring: + + ovs-vsctl add-br br0 + ovs-vsctl add-port br0 eth0 + ovs-vsctl add-port br0 tap0 tag=10 + ovs-vsctl \ + -- --id=@m create mirror name=m0 select-all=true select-vlan=10 \ + output-vlan=15 \ + -- set bridge br0 mirrors=@m + + To later disable mirroring, run: + + ovs-vsctl clear bridge br0 mirrors + + Mirroring to a VLAN can disrupt a network that contains unmanaged + switches. See ovs-vswitchd.conf.db(5) for details. Mirroring to a + GRE tunnel has fewer caveats than mirroring to a VLAN and should + generally be preferred. + +Q: Can I mirror more than one input VLAN to an RSPAN VLAN? + +A: Yes, but mirroring to a VLAN strips the original VLAN tag in favor + of the specified output-vlan. This loss of information may make + the mirrored traffic too hard to interpret. + + To mirror multiple VLANs, use the commands above, but specify a + comma-separated list of VLANs as the value for select-vlan. To + mirror every VLAN, use the commands above, but omit select-vlan and + its value entirely. + + When a packet arrives on a VLAN that is used as a mirror output + VLAN, the mirror is disregarded. Instead, in standalone mode, OVS + floods the packet across all the ports for which the mirror output + VLAN is configured. (If an OpenFlow controller is in use, then it + can override this behavior through the flow table.) If OVS is used + as an intermediate switch, rather than an edge switch, this ensures + that the RSPAN traffic is distributed through the network. + + Mirroring to a VLAN can disrupt a network that contains unmanaged + switches. See ovs-vswitchd.conf.db(5) for details. Mirroring to a + GRE tunnel has fewer caveats than mirroring to a VLAN and should + generally be preferred. + +Q: How do I configure mirroring of all traffic to a GRE tunnel? + +A: The following commands configure br0 with eth0 and tap0 as trunk + ports. All traffic coming in or going out on eth0 or tap0 is also + mirrored to gre0, a GRE tunnel to the remote host 192.168.1.10; any + traffic arriving on gre0 is dropped: + + ovs-vsctl add-br br0 + ovs-vsctl add-port br0 eth0 + ovs-vsctl add-port br0 tap0 + ovs-vsctl add-port br0 gre0 \ + -- set interface gre0 type=gre options:remote_ip=192.168.1.10 \ + -- --id=@p get port gre0 \ + -- --id=@m create mirror name=m0 select-all=true output-port=@p \ + -- set bridge br0 mirrors=@m + + To later disable mirroring and destroy the GRE tunnel: + + ovs-vsctl clear bridge br0 mirrors + ovs-vcstl del-port br0 gre0 + +Q: Does Open vSwitch support ERSPAN? + +A: No. ERSPAN is an undocumented proprietary protocol. As an + alternative, Open vSwitch supports mirroring to a GRE tunnel (see + above). + +Q: How do I connect two bridges? + +A: First, why do you want to do this? Two connected bridges are not + much different from a single bridge, so you might as well just have + a single bridge with all your ports on it. + + If you still want to connect two bridges, you can use a pair of + patch ports. The following example creates bridges br0 and br1, + adds eth0 and tap0 to br0, adds tap1 to br1, and then connects br0 + and br1 with a pair of patch ports. + + ovs-vsctl add-br br0 + ovs-vsctl add-port br0 eth0 + ovs-vsctl add-port br0 tap0 + ovs-vsctl add-br br1 + ovs-vsctl add-port br1 tap1 + ovs-vsctl \ + -- add-port br0 patch0 \ + -- set interface patch0 type=patch options:peer=patch1 \ + -- add-port br1 patch1 \ + -- set interface patch1 type=patch options:peer=patch0 + + Bridges connected with patch ports are much like a single bridge. + For instance, if the example above also added eth1 to br1, and both + eth0 and eth1 happened to be connected to the same next-hop switch, + then you could loop your network just as you would if you added + eth0 and eth1 to the same bridge (see the "Configuration Problems" + section below for more information). + + If you are using Open vSwitch 1.9 or an earlier version, then you + need to be using the kernel module bundled with Open vSwitch rather + than the one that is integrated into Linux 3.3 and later, because + Open vSwitch 1.9 and earlier versions need kernel support for patch + ports. This also means that in Open vSwitch 1.9 and earlier, patch + ports will not work with the userspace datapath, only with the + kernel module. + + +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: + + - OpenFlow flows are the most important kind of flow. OpenFlow + controllers use these flows to define a switch's policy. + OpenFlow flows support wildcards, priorities, and multiple + tables. + + When in-band control is in use, Open vSwitch sets up a few + "hidden" flows, with priority higher than a controller or the + user can configure, that are not visible via OpenFlow. (See + the "Controller" section of the FAQ for more information + about hidden flows.) + + - The Open vSwitch software switch implementation uses a second + 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. + + 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. + + 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
" dumps OpenFlow flows, excluding + hidden flows. This is the most commonly useful form of flow + dump. (Unlike the other commands, this should work with any + OpenFlow switch, not just Open vSwitch.) + + - "ovs-appctl bridge/dump-flows
" dumps OpenFlow flows, + including hidden flows. This is occasionally useful for + troubleshooting suspected issues with in-band control. + + - "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 + kernel-based switches. This command can occasionally be + useful for debugging. + + - "ovs-appctl dpif/dump-flows
", new in Open vSwitch 1.10, + 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 ---------------------- @@ -60,8 +572,8 @@ Q: I created a bridge and added a couple of Ethernet ports to it, 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. + LEDs on my physical switches are blinking, wireshark shows + duplicated packets, and CPU usage is very high. A: More than likely, you've looped your network. Probably, eth0 and eth1 are connected to the same physical Ethernet switch. This @@ -129,10 +641,222 @@ A: Wireless base stations generally only allow packets with the source point, so the same problems will show up with the Linux bridge or any other way to do bridging. +Q: I can't seem to add my PPP interface to an Open vSwitch bridge. + +A: PPP most commonly carries IP packets, but Open vSwitch works only + with Ethernet frames. The correct way to interface PPP to an + Ethernet network is usually to use routing instead of switching. + +Q: Is there any documentation on the database tables and fields? + +A: Yes. ovs-vswitchd.conf.db(5) is a comprehensive reference. + +Q: When I run ovs-dpctl I no longer see the bridges I created. Instead, + I only see a datapath called "ovs-system". How can I see datapath + information about a particular bridge? + +A: In version 1.9.0, OVS switched to using a single datapath that is + shared by all bridges of that type. The "ovs-appctl dpif/*" + commands provide similar functionality that is scoped by the bridge. + +Q: I created a GRE port using ovs-vsctl so why can't I send traffic or + see the port in the datapath? + +A: On Linux kernels before 3.11, the OVS GRE module and Linux GRE module + cannot be loaded at the same time. It is likely that on your system the + Linux GRE module is already loaded and blocking OVS (to confirm, check + dmesg for errors regarding GRE registration). To fix this, unload all + GRE modules that appear in lsmod as well as the OVS kernel module. You + can then reload the OVS module following the directions in INSTALL, + which will ensure that dependencies are satisfied. + + +Quality of Service (QoS) +------------------------ + +Q: How do I configure Quality of Service (QoS)? + +A: Suppose that you want to set up bridge br0 connected to physical + Ethernet port eth0 (a 1 Gbps device) and virtual machine interfaces + vif1.0 and vif2.0, and that you want to limit traffic from vif1.0 + to eth0 to 10 Mbps and from vif2.0 to eth0 to 20 Mbps. Then, you + could configure the bridge this way: + + ovs-vsctl -- \ + add-br br0 -- \ + add-port br0 eth0 -- \ + add-port br0 vif1.0 -- set interface vif1.0 ofport_request=5 -- \ + add-port br0 vif2.0 -- set interface vif2.0 ofport_request=6 -- \ + set port eth0 qos=@newqos -- \ + --id=@newqos create qos type=linux-htb \ + other-config:max-rate=1000000000 \ + queues:123=@vif10queue \ + queues:234=@vif20queue -- \ + --id=@vif10queue create queue other-config:max-rate=10000000 -- \ + --id=@vif20queue create queue other-config:max-rate=20000000 + + At this point, bridge br0 is configured with the ports and eth0 is + configured with the queues that you need for QoS, but nothing is + actually directing packets from vif1.0 or vif2.0 to the queues that + we have set up for them. That means that all of the packets to + eth0 are going to the "default queue", which is not what we want. + + We use OpenFlow to direct packets from vif1.0 and vif2.0 to the + queues reserved for them: + + ovs-ofctl add-flow br0 in_port=5,actions=set_queue:123,normal + ovs-ofctl add-flow br0 in_port=6,actions=set_queue:234,normal + + Each of the above flows matches on the input port, sets up the + appropriate queue (123 for vif1.0, 234 for vif2.0), and then + executes the "normal" action, which performs the same switching + that Open vSwitch would have done without any OpenFlow flows being + present. (We know that vif1.0 and vif2.0 have OpenFlow port + numbers 5 and 6, respectively, because we set their ofport_request + columns above. If we had not done that, then we would have needed + to find out their port numbers before setting up these flows.) + + Now traffic going from vif1.0 or vif2.0 to eth0 should be + rate-limited. + + By the way, if you delete the bridge created by the above commands, + with: + + ovs-vsctl del-br br0 + + then that will leave one unreferenced QoS record and two + unreferenced Queue records in the Open vSwich database. One way to + clear them out, assuming you don't have other QoS or Queue records + that you want to keep, is: + + ovs-vsctl -- --all destroy QoS -- --all destroy Queue + + If you do want to keep some QoS or Queue records, or the Open + vSwitch you are using is older than version 1.8 (which added the + --all option), then you will have to destroy QoS and Queue records + individually. + +Q: I configured Quality of Service (QoS) in my OpenFlow network by + adding records to the QoS and Queue table, but the results aren't + what I expect. + +A: Did you install OpenFlow flows that use your queues? This is the + primary way to tell Open vSwitch which queues you want to use. If + you don't do this, then the default queue will be used, which will + probably not have the effect you want. + + Refer to the previous question for an example. + +Q: I'd like to take advantage of some QoS feature that Open vSwitch + doesn't yet support. How do I do that? + +A: Open vSwitch does not implement QoS itself. Instead, it can + configure some, but not all, of the QoS features built into the + Linux kernel. If you need some QoS feature that OVS cannot + configure itself, then the first step is to figure out whether + Linux QoS supports that feature. If it does, then you can submit a + patch to support Open vSwitch configuration for that feature, or + you can use "tc" directly to configure the feature in Linux. (If + Linux QoS doesn't support the feature you want, then first you have + to add that support to Linux.) + +Q: I configured QoS, correctly, but my measurements show that it isn't + working as well as I expect. + +A: With the Linux kernel, the Open vSwitch implementation of QoS has + two aspects: + + - Open vSwitch configures a subset of Linux kernel QoS + features, according to what is in OVSDB. It is possible that + this code has bugs. If you believe that this is so, then you + can configure the Linux traffic control (QoS) stack directly + with the "tc" program. If you get better results that way, + you can send a detailed bug report to bugs@openvswitch.org. + + It is certain that Open vSwitch cannot configure every Linux + kernel QoS feature. If you need some feature that OVS cannot + configure, then you can also use "tc" directly (or add that + feature to OVS). + + - The Open vSwitch implementation of OpenFlow allows flows to + be directed to particular queues. This is pretty simple and + unlikely to have serious bugs at this point. + + However, most problems with QoS on Linux are not bugs in Open + vSwitch at all. They tend to be either configuration errors + (please see the earlier questions in this section) or issues with + the traffic control (QoS) stack in Linux. The Open vSwitch + developers are not experts on Linux traffic control. We suggest + that, if you believe you are encountering a problem with Linux + traffic control, that you consult the tc manpages (e.g. tc(8), + tc-htb(8), tc-hfsc(8)), web resources (e.g. http://lartc.org/), or + mailing lists (e.g. http://vger.kernel.org/vger-lists.html#netdev). + +Q: Does Open vSwitch support OpenFlow meters? + +A: Since version 2.0, Open vSwitch has OpenFlow protocol support for + OpenFlow meters. There is no implementation of meters in the Open + vSwitch software switch (neither the kernel-based nor userspace + switches). + VLANs ----- +Q: What's a VLAN? + +A: At the simplest level, a VLAN (short for "virtual LAN") is a way to + partition a single switch into multiple switches. Suppose, for + example, that you have two groups of machines, group A and group B. + You want the machines in group A to be able to talk to each other, + and you want the machine in group B to be able to talk to each + other, but you don't want the machines in group A to be able to + talk to the machines in group B. You can do this with two + switches, by plugging the machines in group A into one switch and + the machines in group B into the other switch. + + If you only have one switch, then you can use VLANs to do the same + thing, by configuring the ports for machines in group A as VLAN + "access ports" for one VLAN and the ports for group B as "access + ports" for a different VLAN. The switch will only forward packets + between ports that are assigned to the same VLAN, so this + effectively subdivides your single switch into two independent + switches, one for each group of machines. + + So far we haven't said anything about VLAN headers. With access + ports, like we've described so far, no VLAN header is present in + the Ethernet frame. This means that the machines (or switches) + connected to access ports need not be aware that VLANs are + involved, just like in the case where we use two different physical + switches. + + Now suppose that you have a whole bunch of switches in your + network, instead of just one, and that some machines in group A are + connected directly to both switches 1 and 2. To allow these + machines to talk to each other, you could add an access port for + group A's VLAN to switch 1 and another to switch 2, and then + connect an Ethernet cable between those ports. That works fine, + but it doesn't scale well as the number of switches and the number + of VLANs increases, because you use up a lot of valuable switch + ports just connecting together your VLANs. + + This is where VLAN headers come in. Instead of using one cable and + two ports per VLAN to connect a pair of switches, we configure a + port on each switch as a VLAN "trunk port". Packets sent and + received on a trunk port carry a VLAN header that says what VLAN + the packet belongs to, so that only two ports total are required to + connect the switches, regardless of the number of VLANs in use. + Normally, only switches (either physical or virtual) are connected + to a trunk port, not individual hosts, because individual hosts + don't expect to see a VLAN header in the traffic that they receive. + + None of the above discussion says anything about particular VLAN + numbers. This is because VLAN numbers are completely arbitrary. + One must only ensure that a given VLAN is numbered consistently + throughout a network and that different VLANs are given different + numbers. (That said, VLAN 0 is usually synonymous with a packet + that has no VLAN header, and VLAN 4095 is reserved.) + Q: VLANs don't work. A: Many drivers in Linux kernels before version 3.3 had VLAN-related @@ -150,7 +874,7 @@ A: Many drivers in Linux kernels before version 3.3 had VLAN-related 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 + 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 @@ -207,6 +931,40 @@ A: It's possible that you have the VLAN configured on your physical equally well. Refer to the documentation for the Port table in ovs-vswitchd.conf.db(5) for more information. +Q: I added a pair of VMs on different VLANs, like this: + + ovs-vsctl add-br br0 + ovs-vsctl add-port br0 eth0 + ovs-vsctl add-port br0 tap0 tag=9 + ovs-vsctl add-port br0 tap1 tag=10 + + but the VMs can't access each other, the external network, or the + Internet. + +A: It is to be expected that the VMs can't access each other. VLANs + are a means to partition a network. When you configured tap0 and + tap1 as access ports for different VLANs, you indicated that they + should be isolated from each other. + + As for the external network and the Internet, it seems likely that + the machines you are trying to access are not on VLAN 9 (or 10) and + that the Internet is not available on VLAN 9 (or 10). + +Q: I added a pair of VMs on the same VLAN, like this: + + ovs-vsctl add-br br0 + ovs-vsctl add-port br0 eth0 + ovs-vsctl add-port br0 tap0 tag=9 + ovs-vsctl add-port br0 tap1 tag=9 + + The VMs can access each other, but not the external network or the + Internet. + +A: It seems likely that the machines you are trying to access in the + external network are not on VLAN 9 and that the Internet is not + available on VLAN 9. Also, ensure VLAN 9 is set up as an allowed + trunk VLAN on the upstream switch port to which eth0 is connected. + Q: Can I configure an IP address on a VLAN? A: Yes. Use an "internal port" configured as an access port. For @@ -221,6 +979,50 @@ A: Yes. Use an "internal port" configured as an access port. For ovs-vsctl add-port br0 vlan9 tag=9 -- set interface vlan9 type=internal ifconfig vlan9 192.168.0.7 + See also the following question. + +Q: I configured one IP address on VLAN 0 and another on VLAN 9, like + this: + + ovs-vsctl add-br br0 + ovs-vsctl add-port br0 eth0 + ifconfig br0 192.168.0.5 + ovs-vsctl add-port br0 vlan9 tag=9 -- set interface vlan9 type=internal + ifconfig vlan9 192.168.0.9 + + but other hosts that are only on VLAN 0 can reach the IP address + configured on VLAN 9. What's going on? + +A: RFC 1122 section 3.3.4.2 "Multihoming Requirements" describes two + approaches to IP address handling in Internet hosts: + + - In the "Strong ES Model", where an ES is a host ("End + System"), an IP address is primarily associated with a + particular interface. The host discards packets that arrive + on interface A if they are destined for an IP address that is + configured on interface B. The host never sends packets from + interface A using a source address configured on interface B. + + - In the "Weak ES Model", an IP address is primarily associated + with a host. The host accepts packets that arrive on any + interface if they are destined for any of the host's IP + addresses, even if the address is configured on some + interface other than the one on which it arrived. The host + does not restrict itself to sending packets from an IP + address associated with the originating interface. + + Linux uses the weak ES model. That means that when packets + destined to the VLAN 9 IP address arrive on eth0 and are bridged to + br0, the kernel IP stack accepts them there for the VLAN 9 IP + address, even though they were not received on vlan9, the network + device for vlan9. + + To simulate the strong ES model on Linux, one may add iptables rule + to filter packets based on source and destination address and + adjust ARP configuration with sysctls. + + BSD uses the strong ES model. + 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 @@ -236,12 +1038,135 @@ A: The configuration for VLANs in the Open vSwitch database (e.g. via 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. + controller. In situations where this is not suitable, you can + implement VLAN handling yourself, e.g.: + - If a packet comes in on an access port, and the flow table + needs to send it out on a trunk port, then the flow can add + the appropriate VLAN tag with the "mod_vlan_vid" action. -Controllers ------------ + - If a packet comes in on a trunk port, and the flow table + needs to send it out on an access port, then the flow can + strip the VLAN tag with the "strip_vlan" action. + +Q: I configured ports on a bridge as access ports with different VLAN + tags, like this: + + ovs-vsctl add-br br0 + ovs-vsctl set-controller br0 tcp:192.168.0.10:6633 + ovs-vsctl add-port br0 eth0 + ovs-vsctl add-port br0 tap0 tag=9 + ovs-vsctl add-port br0 tap1 tag=10 + + but the VMs running behind tap0 and tap1 can still communicate, + that is, they are not isolated from each other even though they are + on different VLANs. + +A: Do you have a controller configured on br0 (as the commands above + do)? If so, then this is a variant on the previous question, "My + OpenFlow controller doesn't see the VLANs that I expect," and you + can refer to the answer there for more information. + + +VXLANs +----- + +Q: What's a VXLAN? + +A: VXLAN stands for Virtual eXtensible Local Area Network, and is a means + to solve the scaling challenges of VLAN networks in a multi-tenant + environment. VXLAN is an overlay network which transports an L2 network + over an existing L3 network. For more information on VXLAN, please see + the IETF draft available here: + + http://tools.ietf.org/html/draft-mahalingam-dutt-dcops-vxlan-03 + +Q: How much of the VXLAN protocol does Open vSwitch currently support? + +A: Open vSwitch currently supports the framing format for packets on the + wire. There is currently no support for the multicast aspects of VXLAN. + To get around the lack of multicast support, it is possible to + pre-provision MAC to IP address mappings either manually or from a + controller. + +Q: What destination UDP port does the VXLAN implementation in Open vSwitch + use? + +A: By default, Open vSwitch will use the assigned IANA port for VXLAN, which + is 4789. However, it is possible to configure the destination UDP port + manually on a per-VXLAN tunnel basis. An example of this configuration is + provided below. + + ovs-vsctl add-br br0 + ovs-vsctl add-port br0 vxlan1 -- set interface vxlan1 + type=vxlan options:remote_ip=192.168.1.2 options:key=flow + options:dst_port=8472 + + +Using OpenFlow (Manually or Via Controller) +------------------------------------------- + +Q: What versions of OpenFlow does Open vSwitch support? + +A: The following table lists the versions of OpenFlow supported by + each version of Open vSwitch: + + Open vSwitch OF1.0 OF1.1 OF1.2 OF1.3 OF1.4 + =============== ===== ===== ===== ===== ===== + 1.9 and earlier yes --- --- --- --- + 1.10 yes --- [*] [*] --- + 1.11 yes --- [*] [*] --- + 2.0 yes [*] [*] [*] --- + 2.1 yes [*] [*] [*] --- + 2.2 yes [*] [*] [*] [%] + + [*] Supported, with one or more missing features. + [%] Support is unsafe: ovs-vswitchd will abort when certain + unimplemented features are tested. + + Because of missing features, OpenFlow 1.1, 1.2, and 1.3 must be + enabled manually. The following command enables OpenFlow 1.0, 1.1, + 1.2, and 1.3 on bridge br0: + + ovs-vsctl set bridge br0 protocols=OpenFlow10,OpenFlow11,OpenFlow12,OpenFlow13 + + Use the -O option to enable support for later versions of OpenFlow + in ovs-ofctl. For example: + + ovs-ofctl -O OpenFlow13 dump-flows br0 + + OpenFlow 1.4 is a special case, because it is not implemented + safely: ovs-vswitchd will abort when certain unimplemented features + are tested. Thus, for now it is suitable only for experimental + use. ovs-vswitchd will only allow OpenFlow 1.4 to be enabled + (which must be done in the same way described above) when it is + invoked with a special --enable-of14 command line option. + + OPENFLOW-1.1+ in the Open vSwitch source tree tracks support for + OpenFlow 1.1 and later features. When support for a given OpenFlow + version is solidly implemented, Open vSwitch will enable that + version by default. + +Q: Does Open vSwitch support MPLS? + +A: Before version 1.11, Open vSwitch did not support MPLS. That is, + these versions can match on MPLS Ethernet types, but they cannot + match, push, or pop MPLS labels, nor can they look past MPLS labels + into the encapsulated packet. + + Open vSwitch versions 1.11, 2.0, and 2.1 have very minimal support + for MPLS. With the userspace datapath only, these versions can + match, push, or pop a single MPLS label, but they still cannot look + past MPLS labels (even after popping them) into the encapsulated + packet. Kernel datapath support is unchanged from earlier + versions. + + Open vSwitch version 2.2 will be able to match, push, or pop up to + 3 MPLS labels. Looking past MPLS labels into the encapsulated + packet will still be unsupported. Both userspace and kernel + datapaths will be supported, but MPLS processing always happens in + userspace either way, so kernel datapath performance will be + disappointing. Q: I'm getting "error type 45250 code 0". What's that? @@ -315,6 +1240,294 @@ Q: My OpenFlow controller doesn't see the VLANs that I expect. A: See answer under "VLANs", above. +Q: I ran "ovs-ofctl add-flow br0 nw_dst=192.168.0.1,actions=drop" + but I got a funny message like this: + + ofp_util|INFO|normalization changed ofp_match, details: + ofp_util|INFO| pre: nw_dst=192.168.0.1 + ofp_util|INFO|post: + + and when I ran "ovs-ofctl dump-flows br0" I saw that my nw_dst + match had disappeared, so that the flow ends up matching every + packet. + +A: The term "normalization" in the log message means that a flow + cannot match on an L3 field without saying what L3 protocol is in + use. The "ovs-ofctl" command above didn't specify an L3 protocol, + so the L3 field match was dropped. + + In this case, the L3 protocol could be IP or ARP. A correct + command for each possibility is, respectively: + + ovs-ofctl add-flow br0 ip,nw_dst=192.168.0.1,actions=drop + + and + + ovs-ofctl add-flow br0 arp,nw_dst=192.168.0.1,actions=drop + + Similarly, a flow cannot match on an L4 field without saying what + L4 protocol is in use. For example, the flow match "tp_src=1234" + is, by itself, meaningless and will be ignored. Instead, to match + TCP source port 1234, write "tcp,tp_src=1234", or to match UDP + source port 1234, write "udp,tp_src=1234". + +Q: How can I figure out the OpenFlow port number for a given port? + +A: The OFPT_FEATURES_REQUEST message requests an OpenFlow switch to + respond with an OFPT_FEATURES_REPLY that, among other information, + includes a mapping between OpenFlow port names and numbers. From a + command prompt, "ovs-ofctl show br0" makes such a request and + prints the response for switch br0. + + The Interface table in the Open vSwitch database also maps OpenFlow + port names to numbers. To print the OpenFlow port number + associated with interface eth0, run: + + ovs-vsctl get Interface eth0 ofport + + You can print the entire mapping with: + + ovs-vsctl -- --columns=name,ofport list Interface + + but the output mixes together interfaces from all bridges in the + database, so it may be confusing if more than one bridge exists. + + In the Open vSwitch database, ofport value -1 means that the + interface could not be created due to an error. (The Open vSwitch + log should indicate the reason.) ofport value [] (the empty set) + means that the interface hasn't been created yet. The latter is + normally an intermittent condition (unless ovs-vswitchd is not + running). + +Q: I added some flows with my controller or with ovs-ofctl, but when I + run "ovs-dpctl dump-flows" I don't see them. + +A: ovs-dpctl queries a kernel datapath, not an OpenFlow switch. It + won't display the information that you want. You want to use + "ovs-ofctl dump-flows" instead. + +Q: It looks like each of the interfaces in my bonded port shows up + as an individual OpenFlow port. Is that right? + +A: Yes, Open vSwitch makes individual bond interfaces visible as + OpenFlow ports, rather than the bond as a whole. The interfaces + are treated together as a bond for only a few purposes: + + - Sending a packet to the OFPP_NORMAL port. (When an OpenFlow + controller is not configured, this happens implicitly to + every packet.) + + - Mirrors configured for output to a bonded port. + + It would make a lot of sense for Open vSwitch to present a bond as + a single OpenFlow port. If you want to contribute an + implementation of such a feature, please bring it up on the Open + vSwitch development mailing list at dev@openvswitch.org. + +Q: I have a sophisticated network setup involving Open vSwitch, VMs or + multiple hosts, and other components. The behavior isn't what I + expect. Help! + +A: To debug network behavior problems, trace the path of a packet, + hop-by-hop, from its origin in one host to a remote host. If + that's correct, then trace the path of the response packet back to + the origin. + + Usually a simple ICMP echo request and reply ("ping") packet is + good enough. Start by initiating an ongoing "ping" from the origin + host to a remote host. If you are tracking down a connectivity + problem, the "ping" will not display any successful output, but + packets are still being sent. (In this case the packets being sent + are likely ARP rather than ICMP.) + + Tools available for tracing include the following: + + - "tcpdump" and "wireshark" for observing hops across network + devices, such as Open vSwitch internal devices and physical + wires. + + - "ovs-appctl dpif/dump-flows
" in Open vSwitch 1.10 and + later or "ovs-dpctl dump-flows
" in earlier versions. + These tools allow one to observe the actions being taken on + packets in ongoing flows. + + See ovs-vswitchd(8) for "ovs-appctl dpif/dump-flows" + documentation, ovs-dpctl(8) for "ovs-dpctl dump-flows" + documentation, and "Why are there so many different ways to + dump flows?" above for some background. + + - "ovs-appctl ofproto/trace" to observe the logic behind how + ovs-vswitchd treats packets. See ovs-vswitchd(8) for + documentation. You can out more details about a given flow + that "ovs-dpctl dump-flows" displays, by cutting and pasting + a flow from the output into an "ovs-appctl ofproto/trace" + command. + + - SPAN, RSPAN, and ERSPAN features of physical switches, to + observe what goes on at these physical hops. + + Starting at the origin of a given packet, observe the packet at + each hop in turn. For example, in one plausible scenario, you + might: + + 1. "tcpdump" the "eth" interface through which an ARP egresses + a VM, from inside the VM. + + 2. "tcpdump" the "vif" or "tap" interface through which the ARP + ingresses the host machine. + + 3. Use "ovs-dpctl dump-flows" to spot the ARP flow and observe + the host interface through which the ARP egresses the + physical machine. You may need to use "ovs-dpctl show" to + interpret the port numbers. If the output seems surprising, + you can use "ovs-appctl ofproto/trace" to observe details of + how ovs-vswitchd determined the actions in the "ovs-dpctl + dump-flows" output. + + 4. "tcpdump" the "eth" interface through which the ARP egresses + the physical machine. + + 5. "tcpdump" the "eth" interface through which the ARP + ingresses the physical machine, at the remote host that + receives the ARP. + + 6. Use "ovs-dpctl dump-flows" to spot the ARP flow on the + remote host that receives the ARP and observe the VM "vif" + or "tap" interface to which the flow is directed. Again, + "ovs-dpctl show" and "ovs-appctl ofproto/trace" might help. + + 7. "tcpdump" the "vif" or "tap" interface to which the ARP is + directed. + + 8. "tcpdump" the "eth" interface through which the ARP + ingresses a VM, from inside the VM. + + It is likely that during one of these steps you will figure out the + problem. If not, then follow the ARP reply back to the origin, in + reverse. + +Q: How do I make a flow drop packets? + +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= + + would cause every packet entering switch br0 to be dropped. + + You can write "drop" explicitly if you like. The effect is the + same. Thus, the following command also causes every packet + entering switch br0 to be dropped: + + 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 + + but OVS drops the packets instead. + +A: Yes, OpenFlow requires a switch to ignore attempts to send a packet + out its ingress port. The rationale is that dropping these packets + makes it harder to loop the network. Sometimes this behavior can + even be convenient, e.g. it is often the desired behavior in a flow + that forwards a packet to several ports ("floods" the packet). + + Sometimes one really needs to send a packet out its ingress port + ("hairpin"). In this case, output to OFPP_IN_PORT, which in + ovs-ofctl syntax is expressed as just "in_port", e.g.: + + ovs-ofctl add-flow br0 in_port=2,actions=in_port + + This also works in some circumstances where the flow doesn't match + on the input port. For example, if you know that your switch has + five ports numbered 2 through 6, then the following will send every + received packet out every port, even its ingress port: + + ovs-ofctl add-flow br0 actions=2,3,4,5,6,in_port + + or, equivalently: + + ovs-ofctl add-flow br0 actions=all,in_port + + Sometimes, in complicated flow tables with multiple levels of + "resubmit" actions, a flow needs to output to a particular port + that may or may not be the ingress port. It's difficult to take + advantage of OFPP_IN_PORT in this situation. To help, Open vSwitch + provides, as an OpenFlow extension, the ability to modify the + in_port field. Whatever value is currently in the in_port field is + the port to which outputs will be dropped, as well as the + destination for OFPP_IN_PORT. This means that the following will + reliably output to port 2 or to ports 2 through 6, respectively: + + ovs-ofctl add-flow br0 in_port=2,actions=load:0->NXM_OF_IN_PORT[],2 + ovs-ofctl add-flow br0 actions=load:0->NXM_OF_IN_PORT[],2,3,4,5,6 + + If the input port is important, then one may save and restore it on + the stack: + + ovs-ofctl add-flow br0 actions=push:NXM_OF_IN_PORT[],\ + load:0->NXM_OF_IN_PORT[],\ + 2,3,4,5,6,\ + pop:NXM_OF_IN_PORT[] + +Q: My bridge br0 has host 192.168.0.1 on port 1 and host 192.168.0.2 + on port 2. I set up flows to forward only traffic destined to the + other host and drop other traffic, like this: + + priority=5,in_port=1,ip,nw_dst=192.168.0.2,actions=2 + priority=5,in_port=2,ip,nw_dst=192.168.0.1,actions=1 + priority=0,actions=drop + + But it doesn't work--I don't get any connectivity when I do this. + Why? + +A: These flows drop the ARP packets that IP hosts use to establish IP + connectivity over Ethernet. To solve the problem, add flows to + allow ARP to pass between the hosts: + + priority=5,in_port=1,arp,actions=2 + priority=5,in_port=2,arp,actions=1 + + This issue can manifest other ways, too. The following flows that + match on Ethernet addresses instead of IP addresses will also drop + ARP packets, because ARP requests are broadcast instead of being + directed to a specific host: + + priority=5,in_port=1,dl_dst=54:00:00:00:00:02,actions=2 + priority=5,in_port=2,dl_dst=54:00:00:00:00:01,actions=1 + priority=0,actions=drop + + The solution already described above will also work in this case. + It may be better to add flows to allow all multicast and broadcast + traffic: + + priority=5,in_port=1,dl_dst=01:00:00:00:00:00/01:00:00:00:00:00,actions=2 + priority=5,in_port=2,dl_dst=01:00:00:00:00:00/01:00:00:00:00:00,actions=1 + + +Development +----------- + +Q: How do I implement a new OpenFlow message? + +A: Add your new message to "enum ofpraw" and "enum ofptype" in + lib/ofp-msgs.h, following the existing pattern. Then recompile and + fix all of the new warnings, implementing new functionality for the + new message as needed. (If you configure with --enable-Werror, as + described in INSTALL, then it is impossible to miss any warnings.) + + If you need to add an OpenFlow vendor extension message for a + vendor that doesn't yet have any extension messages, then you will + also need to edit build-aux/extract-ofp-msgs. + + Contact -------