X-Git-Url: http://git.onelab.eu/?a=blobdiff_plain;f=FAQ;h=7488112c5cbd5933f10e35f0272145ccf2128707;hb=485e2766d816a18e1a51ddf5e12e55f38aeedf89;hp=b14bfa4535cef0f670cd4a0ac83b855904018d49;hpb=15d63ed3ac3fe8c7d545a554220ba9d27b17d13b;p=sliver-openvswitch.git diff --git a/FAQ b/FAQ index b14bfa453..7488112c5 100644 --- a/FAQ +++ b/FAQ @@ -113,7 +113,6 @@ A: You can start by joining the mailing lists and helping to answer http://openvswitch.org/mlists/ - Releases -------- @@ -128,46 +127,83 @@ A: All official releases have been through a comprehensive testing supplanted by the next major release. The current LTS release is 1.4.x. -Q: What features are not available in the Open vSwitch kernel datapath - that ships as part of the upstream Linux kernel? +Q: What Linux kernel versions does each Open vSwitch release work with? -A: The kernel module in upstream Linux 3.3 and later does not include - the following features: +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 - - Bridge compatibility, that is, support for the ovs-brcompatd - daemon that (if you enable it) lets "brctl" and other Linux - bridge tools transparently work with Open vSwitch instead. + Open vSwitch userspace should also work with the Linux kernel module + built into Linux 3.3 and later. - We do not expect bridge compatibility to ever be available in - upstream Linux. If you need bridge compatibility, use the - kernel module from the Open vSwitch distribution instead of the - upstream Linux kernel module. + Open vSwitch userspace is not sensitive to the Linux kernel version. + It should build against almost any kernel, certainly against 2.6.18 + and later. - - Tunnel virtual ports, that is, interfaces with type "gre", - "ipsec_gre", "capwap". It is possible to create tunnels in - Linux and attach them to Open vSwitch as system devices. - However, they cannot be dynamically created through the OVSDB - protocol or set the tunnel ids as a flow action. +Q: Should userspace or kernel be upgraded first to minimize downtime? - Work is in progress in adding these features to the upstream - Linux version of the Open vSwitch kernel module. For now, if - you need these features, use the kernel module from the Open - vSwitch distribution instead of the upstream Linux kernel - module. + 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 possbility of incompatibilities. - - Patch virtual ports, that is, interfaces with type "patch". - You can use Linux "veth" devices as a substitute. +Q: What features are not available in the Open vSwitch kernel datapath + that ships as part of the upstream Linux kernel? - We don't have any plans to add patch ports upstream. +A: The kernel module in upstream Linux 3.3 and later does not include + tunnel virtual ports, that is, interfaces with type "gre", + "ipsec_gre", "gre64", "ipsec_gre64", "vxlan", or "lisp". It is + possible to create tunnels in Linux and attach them to Open vSwitch + as system devices. However, they cannot be dynamically created + through the OVSDB protocol or set the tunnel ids as a flow action. + + Work is in progress in adding tunnel virtual ports to the upstream + Linux version of the Open vSwitch kernel module. For now, if you + need these features, use the kernel module from the Open vSwitch + distribution instead of the upstream Linux kernel module. + + The upstream kernel module does not include patch ports, but this + only matters for Open vSwitch 1.9 and earlier, because Open vSwitch + 1.10 and later implement patch ports without using this kernel + feature. Q: What features are not available when using the userspace datapath? -A: Tunnel and patch virtual ports are not supported, as described in the +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. +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 ------------------- @@ -283,6 +319,55 @@ A: No. ERSPAN is an undocumented proprietary protocol. As an alternative, Open vSwitch supports mirroring to a GRE tunnel (see above). +Q: Why are there so many different ways to dump flows? + +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 "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 + 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. + + Each of the commands for dumping flows has a different purpose: + + - "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 exact-match 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 exact-match flows for only the specified bridge, + regardless of the type. + Configuration Problems ---------------------- @@ -410,10 +495,133 @@ 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. + + +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 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). + VLANs ----- @@ -546,6 +754,25 @@ 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: Can I configure an IP address on a VLAN? A: Yes. Use an "internal port" configured as an access port. For @@ -575,8 +802,16 @@ 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. + + - 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: @@ -602,12 +837,24 @@ Controllers Q: What versions of OpenFlow does Open vSwitch support? -A: Open vSwitch supports OpenFlow 1.0. It also includes a number of - extensions that bring many of the features from later versions of - OpenFlow. Work is underway to provide support for later versions and - can be tracked here: +A: Open vSwitch 1.9 and earlier support only OpenFlow 1.0 (plus + extensions that bring in many of the features from later versions + of OpenFlow). - http://openvswitch.org/development/openflow-1-x-plan/ + Open vSwitch versions 1.10 and later will have experimental support + for OpenFlow 1.2 and 1.3. On these versions of Open vSwitch, the + following command enables OpenFlow 1.0, 1.2, and 1.3 on bridge br0: + + ovs-vsctl set bridge br0 protocols=OpenFlow10,OpenFlow12,OpenFlow13 + + Support for OpenFlow 1.1 is incomplete enough that it cannot yet be + enabled, even experimentally. + + Support for OpenFlow 1.2 and 1.3 is still incomplete. Work to be + done is tracked in OPENFLOW-1.1+ in the Open vSwitch source tree + (also via http://openvswitch.org/development/openflow-1-x-plan/). + When support for a given OpenFlow version is solidly implemented, + Open vSwitch will enable that version by default. Q: I'm getting "error type 45250 code 0". What's that? @@ -758,9 +1005,6 @@ A: Yes, Open vSwitch makes individual bond interfaces visible as controller is not configured, this happens implicitly to every packet.) - - The "autopath" Nicira extension action. However, "autopath" - is deprecated and scheduled for removal in February 2013. - - Mirrors configured for output to a bonded port. It would make a lot of sense for Open vSwitch to present a bond as @@ -768,6 +1012,88 @@ A: Yes, Open vSwitch makes individual bond interfaces visible as 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. + Contact -------