  Hybrid IP networks that use both control paradigms - distributed and
centralized - promise the best of two worlds: programmability and agility of
SDN, and reliability and fault tolerance of distributed routing protocols like
OSPF. The common approaches follow a division of labor concept, where SDN
controls prioritized traffic and OSPF assures care-free operation of best
effort traffic. We propose SDN Partitioning, which establishes centralized
control over the distributed routing protocol by partitioning the topology into
sub-domains with SDN-enabled border nodes, such that OSPF's routing updates
have to traverse SDN border nodes to reach neighboring sub-domains. This allows
the central controller to modify how sub-domains view one another, which in
turn allows to steer inter-sub-domain traffic. The degree of dynamic control
against simplicity of OSPF can be trade off by adjusting the size of the
sub-domains. This paper explains the technical requirements, presents a novel
scheme for balanced topology partitioning, and provides the models for common
network management tasks. Our performance evaluation shows that - already in
its minimum configuration with two sub-domains - SDN Partitioning provides
significant improvements in all respects compared to legacy routing protocols,
whereas smaller sub-domains provide network control capabilities comparable to
full SDN deployment.
