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?
Best Answer
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.