[ovs-discuss] VLAN mode=dot1q-tunnel and tags in OVS

Sim Paul simpaul48 at gmail.com
Fri Nov 16 19:46:22 UTC 2018

On Fri, Nov 16, 2018 at 6:00 AM Eric Garver <eric at garver.life> wrote:

> On Thu, Nov 15, 2018 at 03:49:53PM -0800, Sim Paul wrote:
> [..]
> > My concerns are:
> > 1. Shouldn't setting vlan-limit=0, tag=10 push tag=10 on all packets
> > leaving VM1 and i should see tag=10 in tcpdump.
> > 2. Does setting vlan-limit=0 mean i can push unlimited tags on the
> packet ?
> > How can i test this ?
> No. That's not what it means. You can't push more than the datapath
> supports.
> See "vlan-limit" in the ovs-vswitchd.conf man page:
Ok. That means , currently the "maximum" number of VLAN tags supported are 2
which is what the OpenvSwitch userspace currently supports.

I am still trying to understand the test case behavior that i pasted in my
previous email.
In my first test case when vlan-limit=1, the ping worked because
only the outside VLAN tag (36) was inspected ??
But in second case when i set vlan-limit=2, ping stopped working because
both tags 36 and 120 were inspected ?

Shouldn't the ping work even in second test case ?
Pardon my ignorance about vlan tag matching inside the kernel here, but
can someone explain how the packet matching would occur if packet has >= 2
If another tag is forced onto the packet, would that third tag be dropped
or would it replace
an existing tag ?


>     "Value  0  means  unlimited.  The actual number of supported VLAN
>     headers is the smallest of vlan-limit, the number of VLANs sup‐
>     ported by  Open vSwitch userspace (currently 2), and the number
>     supported by the datapath."
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