[ovs-discuss] multicast GRE tunnel problems

[Jesse Gross]

On Thu, Sep 30, 2010 at 7:15 AM, Mike Wray <mike.wray at hp.com> wrote:
>
> I'm trying to use openvswitch to bridge multicast GRE tunnels, but I can't
> get it to work. This is my first go at using openvswitch, so I may be doing
> something wrong.
>
> *) First try: create GRE tunnels using standard linux commands on hosts A
> and B.

Standard Linux GRE tunnels transport IP packets but Open vSwitch deals
with Ethernet frames.  This is why you could ping across the link but
Open vSwitch can't use it.

It is possible to setup Linux GRE for Ethernet frames but you need to
use the ip link command with a type of "gretap".  However, due to a
number of correctness and performance issues (or no support at all)
that vary across Linux kernel versions, we don't support/recommend
using the Linux GRE implementation.

> *) Second try. Use an openvswitch GRE port. On host A clear everything up,
> rmmod ip_gre and start again. Leave host B as-is.
>
> Host A:
> INTF=$(ovs-vsctl create interface name=vtun2 type=gre
> options="local_ip=192.168.1.10,remote_ip=224.10.0.1,key=2")
> PORT=$(ovs-vsctl create port name=vtun2 interfaces=[${INTF}] )
> ovs-vsctl add-br vbr2
> ovs-vsctl add bridge vbr2 ports ${PORT}
> ifconfig vbr2 10.2.0.10/16
>
> Ping from B doesn't work. Using tcpdump I see GRE packets (ARP)
> coming into A on eth0, but nothing on vbr2.
> Doing ping from A I see GRE packets (ARP) coming into B on eth0,
> but tcpdump on vtun2 shows strange stuff with ethertype 0x6558.
> So there might be an interoperability problem.

EtherType 0x6558 is the GRE type for Ethernet frames, which is what
Open vSwitch needs.  If Linux is configured in this mode, it uses the
same EtherType.

>
> *) Third try. Use openvswitch GRE ports at both ends.
> Leave A as-is, setup GRE using ovs-vsctl on B.
> Ping from B doesn't work. I see GRE packets (ARP) going out eth0 on B
> and coming in eth0 on A but nothing on the vbr2 bridge.

This configuration would normally work.  However, multicast isn't
currently implemented in the Open vSwitch GRE stack.  It's planned and
it shouldn't be too much work but it hasn't been done yet.