[ovs-discuss] GRE tunnel with 0.99.2 snapshot

Jesse Gross jesse at nicira.com
Thu Mar 25 15:42:14 UTC 2010

On Thu, Mar 25, 2010 at 4:10 AM, Lee, Jeongkeun <jklee at hp.com> wrote:

> Hi,
> Does the current snapshot support GRE tunnel?
> Based on the mailing list logs, gre support is under development and will
> be a part of the next release.

There is a prototype version of GRE support currently checked into the
master branch that is based on the Linux GRE code but a more integrated
version is currently under development.

> I just tried to attach a gre interface (created by linux 'ip') by ovs-vsctl
> add-port and ovs-dpctl add-if but none of them worked. I wonder there is any
> APIs used for testing.

If it didn't attach at all, it is probably because the type specified to the
ip command was "gre" instead of "gretap".  "gre" is for IP over GRE, whereas
"gretap" is for Ethernet over GRE.  However, the Linux GRE implementation
has a number of bugs, both generally and specifically when used for
bridging, the severity of which depend on the kernel version.  However, all
versions have some issues so I would not recommend using it.

> I found a mention about gre interface type in the ovs-vswichtd.conf.db man
> page, though..

 The OVS tree currently includes a modified version of the Linux GRE module
with a number of bug fixes and enhancements.  It also includes support for
setting up tunnels directly from the OVS config protocol.  To use it you
have to:

1. Unload the Linux ip_gre module if it already loaded
2. Load the OVS GRE module (ip_gre_mod.ko in the same directory as the main
OVS module).
3. Create an interface of type "gre" using the config protocol.  The options
field on the interface has several GRE specific choices such as remote_ip,
local_ip, key, etc.
4. Connect the interface to a bridge and use it like a normal port.
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