X-Git-Url: http://git.onelab.eu/?a=blobdiff_plain;f=FAQ;h=a98739cb36fc6fd387f9d602a378b82ea98887d5;hb=31ce74a9f05312e3d68e55034b23ff2690a91ce7;hp=678ca2cffc9e306fdf28a4c02f96de8eac338596;hpb=c483d489caeec8b38991065580365e8a2b34237e;p=sliver-openvswitch.git diff --git a/FAQ b/FAQ index 678ca2cff..a98739cb3 100644 --- a/FAQ +++ b/FAQ @@ -3,6 +3,287 @@ 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, + 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 2.6.18 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-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. + +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 + 1.4.x. + +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 3.3 and later does not include + the following features: + + - 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. + + 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. + + - 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. + + 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. + + - Patch virtual ports, that is, interfaces with type "patch". + You can use Linux "veth" devices as a substitute. + + We don't have any plans to add patch ports upstream. + +Q: What features are not available when using the userspace datapath? + +A: Tunnel and patch 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. + + +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: 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). + + Configuration Problems ---------------------- @@ -60,8 +341,8 @@ 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 +410,68 @@ 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: Is there any documentation on the database tables and fields? + +A: Yes. ovs-vswitchd.conf.db(5) is a comprehensive reference. + 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 +489,7 @@ 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 @@ -239,10 +578,37 @@ A: The configuration for VLANs in the Open vSwitch database (e.g. via controller. This will only be suitable for some situations, though. +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. + 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: + + http://openvswitch.org/development/openflow-1-x-plan/ + Q: I'm getting "error type 45250 code 0". What's that? A: This is a Open vSwitch extension to OpenFlow error codes. Open @@ -315,6 +681,72 @@ 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. + Contact -------