Hi there,

However,
this would mean a shift from VPLS to VXLAN.
On this particular sentence - it is incorrect to compare VPLS and VXLAN. One is a set of control plane mechanisms for discovery and tunnel setup and data plane encapsulations and multipoint reachability model, while the other is just a data plane encapsulation. VXLAN is equivalent to a (point to point) pseudowire used as a data plane component in VPLS.



2) Traffic engineering - we don't have a lot of requirement for this, but do
    have a small number of customers who buy A and B circuits, and require them
    to be routed across different paths on our network. This is easy with MPLS
    using explicit LSPs, but we've not yet worked out how to achieve the same
    thing in VXLAN.
VXLAN is a tunnel over a routed IP network. The path to reach the tunnel endpoint will define how VXLAN encapsulated payload is traversing over your network. If tunnel endpoint is reachable via explicitly routed LSP, the payload will follow that path. VXLAN by itself does nothing to influence the underlay path.

So, my question to the community is - have any of you used VXLAN as a wide-area
layer 2 transport technology?
Yes, there are such deployments. The number of such deployments is increasing.

Any pros or cons? Gotchas? Scare stories?
Recommendations? Am I trying to shoot myself in the foot?

VXLAN is a tunnelling mechanism. You seem to be looking for a end to end solution, for which VXLAN is a (rather small) component. You need to start from the requirements. What is the underlay technology being used? How much of traffic engineering functionality will be required, and how the particular underlay technology can implement it? What about ECMP support and requirements for its use - flow mapping to VXLAN tunnel is the same problem as flow mapping to any other tunnel in underlay ECMP environment. To build all of this is one thing, but to operate is quite the other - what about OAM requirements? VXLAN has no OAM support, and will not get one. If your operations systems rely on MPLS based OAM for service layer (eg, an MPLS based PW) - that will not be available. How the tunnels will be set up - is there a need to do discovery, or will all of it be orchestrated?

Two main limiting factors in VXLAN applicability are lack of payload type indicator - the tunnel can carry only a single type of payload (ethernet in the canonic definition, no possibility to use single tunnel for multiple user payload types without additional encapsulation), and no ability to indicate that the payload is not a user payload but some other special type like OAM (pseudowire control word would be an example of such indicator). This leaves VXLAN as a solution of limited applicability for anything else than original intended one - ethernet tunnel over IP underlay. For other uses VXLAN is of limited applicability, there may be (and in fact are) vendor specific extensions but there is no point in talking about interoperability then. This problem space is well understood and there are successors to VXLAN - Geneve is getting into good shape (there are vendor specific early implementations but it is too early to talk about interoperability at this time), plus different vendors have their own tunnel encapsulation mechanisms (VXLAN-GPE being a more visible one, however it is not going to be standardized soon).

The other interesting part to solve is the control plane. BGP based one will likely be the most practical option here. Combined with ability to tunnel multiple payload types this gives you a single control plane for L3VPN and point to point and multipoint L2VPN built on the same underlay with the single tunnelling mechanism. Your operations team will thank you violently for doing this.

Ignas

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