Thanks for the replies, I have some further responses below. On Sun, Jul 31, 2016 at 08:22:47AM +0800, Xiao Liang wrote: > On Thu, Jul 28, 2016 at 2:40 AM, Ben Pfaff <b...@ovn.org> wrote: > > I'm concerned about backward compatibility. Consider some application > > built on Open vSwitch using OpenFlow. Today, it can distinguish > > single-tagged and double-tagged packets (that use outer Ethertype > > 0x8100), as follows: > > > > - A single-tagged packet has vlan_tci != 0 and some non-VLAN > > dl_type. > > > > - A double-tagged packet has vlan_tci != 0 and a VLAN dl_type. > > > > With this patch, this won't work, because neither kind of packet has a > > VLAN dl_type. Instead, applications need to first match on the outer > > VLAN, then pop it off, then match on the inner VLAN. This difference > > could lead to security problems in applications. An application > > might, for example, want to pop an outer VLAN and forward the packet, > > but only if there is no inner VLAN. If it is implemented according to > > the previous rules, then it will not notice the inner VLAN. > > Maybe some applications are implemented this way, but they are > probably wrong. OpenFlow says eth_type is "ethernet type of the > OpenFlow packet payload, after VLAN tags", so it is the payload > ethtype for a double-tagged packet. It's the same for single-tagged > packet: application must explicitly match vlan_tci to decide whether > it has VLAN tag.
OpenFlow does say that, but it's inconsistent with long-standing Open vSwitch practice and will cause backward incompatibility and, worse, security problems. If we need the official OpenFlow behavior then I think we'll need to add a feature switch to turn on that behavior. > > This code uses the term "shift" for what is usually termed "push". A > > "shift" can go in either direction. I'd use "push". > > > Yes, "push" looks symmetric. I used "shift" because it leaves room for > a header rather than push data. Sometimes we use the longer name "push_uninit" in Open vSwitch to make it clear that what is being pushed is not initialized, for example see dp_packet_push_uninit(), nl_msg_push_uninit(), ofpbuf_push_uninit() and the related ds_put_uninit(). However, when I look at your calls to the "shift" function, it looks like most of them could easily be written to provide the new header contents as an argument. _______________________________________________ dev mailing list dev@openvswitch.org http://openvswitch.org/mailman/listinfo/dev
