  This paper studies the resilient routing and (in-band) fast failover
mechanisms supported in Software-Defined Networks (SDN). We analyze the
potential benefits and limitations of such failover mechanisms, and focus on
two main metrics: (1) correctness (in terms of connectivity and loop-freeness)
and (2) load-balancing. We make the following contributions. First, we show
that in the worst-case (i.e., under adversarial link failures), the usefulness
of local failover is rather limited: already a small number of failures will
violate connectivity properties under any fast failover policy, even though the
underlying substrate network remains highly connected. We then present
randomized and deterministic algorithms to compute resilient forwarding sets;
these algorithms achieve an almost optimal tradeoff. Our worst-case analysis is
complemented with a simulation study.
