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 Troubleshoot Open vSwitch

Open vSwitch as used in the previous OpenStack Networking Service examples is a full-featured multilayer virtual switch licensed under the open source Apache 2.0 license. Full documentation can be found at the project's website. In practice, given the preceding configuration, the most common issues are being sure that the required bridges (br-int, br-tun, br-ex, etc.) exist and have the proper ports connected to them.

The Open vSwitch driver should and usually does manage this automatically, but it is useful to know how to do this by hand with the ovs-vsctl command. This command has many more subcommands than we will use here; see the man page or use ovs-vsctl --help for the full listing.

To list the bridges on a system, use ovs-vsctl list-br. This example shows a compute node that has an internal bridge and a tunnel bridge. VLAN networks are trunked through the eth1 network interface:

# ovs-vsctl list-br
br-int
br-tun
eth1-br
      

Working from the physical interface inwards, we can see the chain of ports and bridges. First, the bridge eth1-br, which contains the physical network interface eth1 and the virtual interface phy-eth1-br:

# ovs-vsctl list-ports eth1-br
eth1
phy-eth1-br
      

Next, the internal bridge, br-int, contains int-eth1-br, which pairs with phy-eth1-br to connect to the physical network shown in the previous bridge, patch-tun, which is used to connect to the GRE tunnel bridge and the TAP devices that connect to the instances currently running on the system:

# ovs-vsctl list-ports br-int
int-eth1-br
patch-tun
tap2d782834-d1
tap690466bc-92
tap8a864970-2d
      

The tunnel bridge, br-tun, contains the patch-int interface and gre-<N> interfaces for each peer it connects to via GRE, one for each compute and network node in your cluster:

# ovs-vsctl list-ports br-tun
patch-int
gre-1
.
.
.
gre-<N>
      

If any of these links is missing or incorrect, it suggests a configuration error. Bridges can be added with ovs-vsctl add-br, and ports can be added to bridges with ovs-vsctl add-port. While running these by hand can be useful debugging, it is imperative that manual changes that you intend to keep be reflected back into your configuration files.

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