So, I've been checking Google along with the RFC 7348 about VxLAN functionality. I believe I do have a good grasp of what the purpose of the protocol is, what it does and how it does it etc but I fail to see the purpose of the Optional Outer 802.1Q. The RFC standard states (page 11):

The outer VLAN tag is optional. If present, it may be used for delineating VXLAN traffic on the LAN.

Can anyone help me with this part of the sentence? What does "delineating VXLAN traffic on the VLAN implies"? What does this do? :S
As far as I understand it, the Optional Inner 802.1Q serves the purpose to forward traffic in already established VLAN environments. In essence, it "stretches" existing L2 infrastructures by expanding their number of available groups to ~16M from ~4K by also offering L3 isolation which is the whole point after all. But what about the Outer 802.1Q? What am I missing here?

  • what problem are you trying to solve? certification/education questions are generally off topic... – Craig Constantine Apr 14 '16 at 14:50
  • I'm not taking any certifications. What do you mean by 'education'? If you mean homework nope. In general, I'm using OpenStack and have studied a whole lot of things about it. One of the many things I studied is VxLAN but this specific thing I asked has eluded me ever since. It's not important since I do not need it anywhere but it's nice to know what is its purpose and this is why I'm asking (especially if you're studying/advising the RFC standard which is ... the standard itself!) ;) – Kounavi Apr 14 '16 at 15:20
  • Did any answer help you? If so, you should accept the answer so that the question doesn't keep popping up forever, looking for an answer. Alternatively, you could provide and accept your own answer. – Ron Maupin Aug 14 '17 at 1:14

Presumably, the outer vlan ID is used if you want to carry both your VXLAN trunk and a bunch of other non-VXLAN VLANs together on a traditional 802.1q trunk. So you end up with an outer .1q trunk just like you've always done, and an inner VXLAN trunk. The switches involved in this trunk have no knowledge of VXLAN, to them it's just another flow, like any other UDP traffic.

  • Well, that's what I've come to conclude which actually does make sense but I wanted some sort of confirmation. Thanks a lot! :) – Kounavi Apr 14 '16 at 17:14

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