  Flexibility is often claimed as a competitive advantage when proposing new
network designs. However, most proposals provide only qualitative arguments for
their improved support of flexibility. Quantitative arguments vary a lot among
different proposals. A general understanding for flexibility is not yet clearly
defined, leaving it to the reader to draw the right conclusions based on
background information. The term flexibility is commonly defined as the ability
to adapt to changes. For networks, flexibility would refer to the ability to
adapt the available network resources, such as flows or topology, to changes of
design requirements, e.g., shorter latency budgets or different traffic
distributions. Recent concepts such as Software Defined Networking, Network
Virtualization and Network Function Virtualization have emerged claiming to
provide more flexibility in networks. Nevertheless, a deeper understanding of
what flexibility means and how it could be quantified to compare different
network designs remains open. In this paper, we ask whether flexibility can be
a new measure for network design space analysis. As it is quite challenging to
formulate a flexibility measure that covers all network aspects, we propose an
initial set of flexibility aspects to start grounding guidelines. Our initial
selection is backed up by an analysis of Software Defined Networking, Network
Virtualization and Network Function Virtualization for their support of the
selected flexibility aspects. Our research methodology is based on a systematic
approach that leads to network design guidelines with respect to flexibility.
