We present a formal model of network protocols and their application
to modeling firewall policies. The formalization is based on the
\emph{Unified Policy Framework} (UPF)~\cite{brucker.ea:upf:2014}. The
formalization was originally developed with for generating test cases
(see~\cite{brucker.ea:formal-fw-testing:2014} for details) for testing the
security configuration actual firewall and router (middle-boxes) using
HOL-TestGen~\cite{brucker.ea:formal-fw-testing:2014}. Our work focuses
on modeling application level protocols on top of tcp/ip. Thus, its
abstraction level differs from Diekmann's Network Security Policy
Verification
formalization~\cite{Network_Security_Policy_Verification-AFP}.