Using Open vSwitch as a Simple OpenFlow Switch ============================================== Open vSwitch uses OpenFlow as its preferred method of remote flow table configuration. This is the simplest method of using it with an OpenFlow controller. The ovs-vsctl "set-controller" command can also be used in conjunction with ovs-vswitchd to set the controller for one or more bridges. We recommend using OpenFlow in this manner and in this case you should not run ovs-openflowd. Directions for setting up ovs-vswitchd can be found in INSTALL.Linux. However, it is also possible to use Open vSwitch as a simple OpenFlow switch like that provided by the OpenFlow reference implementation [1]. The remainder of this file describes how to use it in that manner. What is OpenFlow? ----------------- OpenFlow is a flow-based switch specification designed to enable researchers to run experiments in live networks. OpenFlow is based on a simple Ethernet flow switch that exposes a standardized interface for adding and removing flow entries. An OpenFlow switch consists of three parts: (1) A "flow table" in which each flow entry is associated with an action telling the switch how to process the flow, (2) a "secure channel" that connects the switch to a remote process (a controller), allowing commands and packets to be sent between the controller and the switch, and (3) an OpenFlow protocol implementation, providing an open and standard way for a controller to talk to the switch. An OpenFlow switch can thus serve as a simple datapath element that forwards packets between ports according to flow actions defined by the controller using OpenFlow commands. Example actions are: - Forward this flow's packets to the given port(s) - Drop this flow's packets - Encapsulate and forward this flow's packets to the controller. The OpenFlow switch is defined in detail in the OpenFlow switch Specification [2]. Installation Procedure ---------------------- The procedure below explains how to use the Open vSwitch as a simple OpenFlow switch. 1. Build and install the Open vSwitch kernel modules and userspace programs as described in INSTALL.Linux. It is important to run "make install", because some Open vSwitch programs expect to find files in locations selected at installation time. 2. Load the openvswitch kernel module (which was built in step 1), e.g.: % insmod datapath/linux-2.6/openvswitch_mod.ko If your Linux kernel is earlier than 2.6.36, this kernel module cannot be loaded if the Linux bridge module is already loaded. Thus, you may need to remove any existing bridges and unload the bridge module with "rmmod bridge" before you can do this. 3. Create a datapath instance. The command below creates a datapath identified as dp0 (see ovs-dpctl(8) for more detailed usage information). # ovs-dpctl add-dp dp0 Creating datapath dp0 creates a new network device, also named dp0. This network device, called the datapath's "local port", will be bridged to the physical switch ports by ovs-openflowd(8). It is optionally used for in-band control as described in step 5. 4. Use ovs-dpctl to attach the datapath to physical interfaces on the machine. Say, for example, you want to create a trivial 2-port switch using interfaces eth1 and eth2, you would issue the following commands: # ovs-dpctl add-if dp0 eth1 # ovs-dpctl add-if dp0 eth2 You can verify that the interfaces were successfully added by asking ovs-dpctl to print the current status of datapath dp0: # ovs-dpctl show dp0 5. Arrange so that the switch can reach the controller over the network. This can be done in two ways. The switch may be configured for out-of-band control, which means it uses a network separate from the data traffic that it controls. Alternatively, the switch may be configured to contact the controller over one of the network devices under its control. In-band control is often more convenient than out-of-band, because it is not necessary to maintain two independent networks. - If you are using out-of-band control, at this point make sure that the switch machine can reach the controller over the network. - If you are using in-band control, then at this point you must configure the dp0 network device created in step 3. This device is not yet bridged to any physical network (because ovs-openflowd does that, and it is not yet running), so the next step depends on whether connectivity is required to configure the device's IP address: * If the switch has a static IP address, you may configure its IP address now, e.g.: # ifconfig dp0 192.168.1.1 * If the switch does not have a static IP address, e.g. its IP address is obtained dynamically via DHCP, then proceed to the next step. The DHCP client will not be able to contact the DHCP server until the secure channel has started. The address will be obtained in step 7. 6. Run ovs-openflowd to start the secure channel connecting the datapath to a remote controller. If the controller is running on host 192.168.1.2 port 6633 (the default port), the ovs-openflowd invocation would look like this: # ovs-openflowd dp0 tcp:192.168.1.2 - If you are using out-of-band control, add --out-of-band to the command line. Using the "tcp:" argument causes the switch to connect in an insecure manner. Please see INSTALL.SSL for a description of how to connect securely using SSL. 7. If you are using in-band control, and the switch obtains its IP address dynamically, then you may now obtain the switch's IP address, e.g. by invoking a DHCP client. The secure channel will only be able to connect to the controller after an IP address has been obtained. 8. The secure channel should connect to the controller within a few seconds. References ---------- [1] OpenFlow Reference Implementation. [2] OpenFlow Switch Specification.