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SNAP: Stateful Network-Wide Abstractions for Packet Processing

Report ID:
July 5, 2016
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Early programming languages for software-defined networking
(SDN) were built on top of the simple matchaction
paradigm offered by OpenFlow 1.0. However,
emerging hardware and software switches offer much
more sophisticated support for persistent state in the
data plane, without involving a central controller. Nevertheless,
managing stateful, distributed systems effi-
ciently and correctly is known to be one of the most
challenging programming problems. To simplify this
new SDN problem, we introduce SNAP.
SNAP offers a simpler “centralized” stateful programming
model, by allowing programmers to develop programs
on top of one big switch rather than many. These
programs may contain reads and writes to global, persistent
arrays, and as a result, programmers can implement
a broad range of applications, from stateful
firewalls to fine-grained traffic monitoring. The SNAP
compiler relieves programmers of having to worry about
how to distribute, place, and optimize access to these
stateful arrays by doing it all for them. More specifically,
the compiler discovers read/write dependencies
between arrays and translates one-big-switch programs
into an efficient internal representation based on a novel
variant of binary decision diagrams. This internal representation
is used to construct a mixed-integer linear
program, which jointly optimizes the placement of state
and the routing of traffic across the underlying physical
topology. We have implemented a prototype compiler
and applied it to about 20 SNAP programs over various
topologies to demonstrate our techniques’ scalability.

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