[donavanm]

I haven’t worked in the space in a while but I’d doubt it’s via anything like HTTP headers. From a total guess I’d look at packet inter frame gaps & jitter to imply client csmacd or l2 behavior. Maaaaybe MTU and TTLs to infer intermediate routed networks or devices like the tunnel. And of course various TCP options and behavior, like say timestamps and dsack, to fingerprint the client or intervening ip proxies.