Software transactional networking: concurrent and consistent policy composition
http://dl.acm.org/citation.cfm?id=2491200
fine-grained locking on network components and avoids complex state machine replication.
… logically centralized, important considerations such as high availability, responsiveness, and scalability dictate that a robust control platform be realized as a distributed system.
… multi-authorship of network policy, we face the issues of policy composition and conflict resolution.
Onix realizes a control platform that relies on existing distributed systems techniques and builds upon the notion of a Network Information Base (NIB), i.e., a data structure that maintains a copy of the network state.
- strongly consistent policy composition
- results in all data plane traffic experiencing the same globally
ordered sequence of composed policy updates.
Implementing strongly consistent transactional synchronization can be achieved by centrally serializing the requests at a single master controller or using state-machine replication.
a surprisingly simple light-weight implementation of it that only
requires low-level, per-switch port conflict resolution, which can be
implemented by, e.g., maintaining one lock per hardware switch. Our
implementation assumes that sequential composition rules are
explicitly (but possibly incompletely) specified using the earlier
work [2,3],
- weakly consistent policy composition
- allows different traffic flows to experience differently ordered sequences of composed policy updates.
2. CONCURRENT COMPOSITION
references
- [2] A. D. Ferguson, A. Guha, C. Liang, R. Fonseca, and S. Krishnamurthi. Hierarchical Policies for Software Defined Networks. In HotSDN, 2012.
- [3] N. Foster, R. Harrison, M. J. Freedman, C. Monsanto, J. Rexford, A. Story, and D. Walker. Frenetic: A Network Programming Language. In ACM ICFP, 2011.
The Case for Reliable Software Transactional Networking
This paper initiates the study of the SDN control plane as a distributed system.
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overlapping policy-update requests may arbitrarily interleave with traffic-related events.
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the abstraction of Consistent Policy Composition (CPC)
- CPC abstraction offers a transactional interface.
- wait-free CPC algorithm, called
Tagwhich incurs exponential (in the size of the network) overhead on the packet size and the switch memory. - a slightly more powerful SDN switch interface supporting an atomic read-modify-write allows for a wait-free CPC solution, i.e., tolerating n−1 failures out of n controllers.
2 consistent policy composition
the existence of HS establishes that H is sequentially composable
