  In various contexts of networking research, end-host path selection has
recently regained momentum as a design principle. While such path selection has
the potential to increase performance and security of networks, there is a
prominent concern that it could also lead to network instability (i.e.,
flow-volume oscillation) if paths are selected in a greedy, load-adaptive
fashion. However, the extent and the impact vectors of instability caused by
path selection are rarely concretized or quantified, which is essential to
discuss the merits and drawbacks of end-host path selection.
  In this work, we investigate the effect of end-host path selection on various
metrics of networks both qualitatively and quantitatively. To achieve general
and fundamental insights, we leverage the recently introduced axiomatic
perspective on congestion control and adapt it to accommodate joint algorithms
for path selection and congestion control, i.e., multi-path congestion-control
protocols. Using this approach, we identify equilibria of the multi-path
congestion-control dynamics and analytically characterize these equilibria with
respect to important metrics of interest in networks (the 'axioms') such as
efficiency, fairness, and loss avoidance. Moreover, we analyze how these
axiomatic ratings for a general network change compared to a scenario without
path selection, thereby obtaining an interpretable and quantititative
formalization of the performance impact of end-host path-selection. Finally, we
show that there is a fundamental trade-off in multi-path congestion-control
protocol design between efficiency, stability, and loss avoidance on one side
and fairness and responsiveness on the other side.
