  With the ongoing exhaustion of free address pools at the registries serving
the global demand for IPv4 address space, scarcity has become reality. Networks
in need of address space can no longer get more address allocations from their
respective registries.
  In this work we frame the fundamentals of the IPv4 address exhaustion
phenomena and connected issues. We elaborate on how the current ecosystem of
IPv4 address space has evolved since the standardization of IPv4, leading to
the rather complex and opaque scenario we face today. We outline the evolution
in address space management as well as address space use patterns, identifying
key factors of the scarcity issues. We characterize the possible solution space
to overcome these issues and open the perspective of address blocks as virtual
resources, which involves issues such as differentiation between address
blocks, the need for resource certification, and issues arising when
transferring address space between networks.
