  QUIC offers security and privacy for modern web traffic by closely
integrating encryption into its transport functionality. In this process, it
hides transport layer information often used for network monitoring, thus
obsoleting traditional measurement concepts. To still enable passive RTT
estimations, QUIC introduces a dedicated measurement bit - the spin bit. While
simple in its design, tracking the spin bit at line-rate can become challenging
for software-based solutions. Dedicated hardware trackers are also unsuitable
as the spin bit is not invariant and can change in the future. Thus, this paper
investigates whether P4-programmable hardware, such as the Intel Tofino, can
effectively track the spin bit at line-rate. We find that the core
functionality of the spin bit can be realized easily, and our prototype has an
accuracy close to software-based trackers. Our prototype further protects
against faulty measurements caused by reordering and prepares the data
according to the needs of network operators, e.g., by classifying samples into
pre-defined RTT classes. Still, distinct concepts in QUIC, such as its
connection ID, are challenging with current hardware capabilities.
