  Segment routing (SR) offers precise control over the paths taken: it
specifies a list of detours, called segments, in IP packets. However, the
number of detours that can be specified is limited by the hardware. When
calculating segment lists, it is therefore necessary to limit their size.
Although solutions have been proposed for calculating these lists, they lack
generality and are not always optimal or efficient. We present ROUTOURNE, a
method for diverting routing algorithms so that they calculate, not simply an
optimal physical path to be translated into a list of segments a posteriori
(with no guarantee of its size), but directly the optimal lists of segments
deployable by the underlying hardware. ROUTOURNE thus facilitates the
deployment of advanced traffic engineering strategies and policies, notably for
load balancing from sources. Despite a route fraught with surprising challenges
- in particular, the loss of isotonicity induced by SR - ROUTOURNE proves
efficient, inducing at worst a linear overhead. Its accuracy and optimality
have been proven, and its effectiveness evaluated by generalizing it to several
more or less complex path calculation algorithms.
