  Enterprise networks that host valuable assets and services are popular and
frequent targets of distributed network attacks. In order to cope with the
ever-increasing threats, industrial and research communities develop systems
and methods to monitor the behaviors of their assets and protect them from
critical attacks. In this paper, we systematically survey related research
articles and industrial systems to highlight the current status of this arms
race in enterprise network security. First, we discuss the taxonomy of
distributed network attacks on enterprise assets, including distributed
denial-of-service (DDoS) and reconnaissance attacks. Second, we review existing
methods in monitoring and classifying network behavior of enterprise hosts to
verify their benign activities and isolate potential anomalies. Third,
state-of-the-art detection methods for distributed network attacks sourced from
external attackers are elaborated, highlighting their merits and bottlenecks.
Fourth, as programmable networks and machine learning (ML) techniques are
increasingly becoming adopted by the community, their current applications in
network security are discussed. Finally, we highlight several research gaps on
enterprise network security to inspire future research.
