[ovs-discuss] Error trying to add flow with strip_vlan action

Nikhil Handigol nikhil.handigol at gmail.com
Wed Sep 17 22:03:11 UTC 2014


On Wed, Sep 17, 2014 at 2:22 PM, Ben Pfaff <blp at nicira.com> wrote:

> On Wed, Sep 17, 2014 at 11:49:26AM -0700, Nikhil Handigol wrote:
> > I've setup an OVS bridge br0 with the following commands:
> > $ sudo ovs-vsctl add-br br0
> > $ sudo ovs-vsctl set bridge br0
> > protocols=OpenFlow10,OpenFlow11,OpenFlow12,OpenFlow13
> > $ sudo ovs-vsctl set bridge br0 datapath_type=netdev
> >
> >
> > I tried to insert the following flow with a strip_vlan action:
> > $ sudo ovs-ofctl -O OpenFlow13 add-flow br0 "cookie=0x0, table=1,
> > send_flow_rem
> >
> priority=30,vlan_tci=0x0ffe/0x1fff,arp,metadata=0xffffffff00000000,arp_tpa=10.0.0.1
> > actions=strip_vlan,write_metadata:0xcafecafe00000000,goto_table:2"
> >
> > I get the following error:
> > ovs-ofctl: none of the usable flow formats (none) is among the allowed
> flow
> > formats (OXM-OpenFlow13)
> >
> > However when I remove "strip_vlan" from the actions, the flow gets added
> > correctly. What am I doing wrong?
>
> vlan_tci=0xffe/0x1fff looks confused, to me.  It cannot ever match any
> packets, because it looks for a packet with no VLAN header (because bit
> 12 is not set in the value) but a nonzero VLAN ID (because bits 0-11 are
> nonzero in the value).
>
> I imagine that the root of the problem, though, is that (based on bit 12
> of vlan_tci) the flow's packets have no VLAN yet the actions are trying
> to strip a VLAN header.
>

Why does bit 12 set to 0 indicate absence of VLAN header? According to the
wiki page (http://en.wikipedia.org/wiki/IEEE_802.1Q), bit 12 is DEI, which
specifies whether packets can be dropped when there is congestion. So, it
seems like both 0 and 1 are valid values for bit 12.
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