Session 3, Paper 1: Reclaiming the Brain: Useful OpenFlow Functions in the Data Plane

Authors: Michael Borokhovich (Ben Gurion University, Israel), Liron Schiff (Tel Aviv University, Israel), Stefan Schmid (TU Berlin and T-Labs, Germany)

Link to paper: Reclaiming the Brain: Useful OpenFlow Functions in the Data Plane

SDN simplifies network management by providing programmatic interface to a logically centralized controller, allowing splitting network into a “dumb” data plane and a “smart” control plane. This, however, comes with a cost: fine-grain control of the data plane would introduce computational overhead and latency in the control plane. This paper investigates which functionalities to add in the OpenFlow data plane (“south”), making it smarter to reduce interactions with the control plane and network more robust.

The approach in this paper relies on a simple template called “SmartSouth”, an in-band graph DFS traversal implemented using the match-action paradigm, using fast failover technique. In general, monitoring and communication functions are added to the “south” to make it more robust, proactively react to link failures and reduce interaction with control plane. Specifically, functions which are provided in the south: 

• Topology snapshot: collects current view of network topology; fault-tolerant, no connectivity assumed; single connection to controller is required 
• Blackhole detection: detects connectivity loss, regardless of the causes (e.g., physical failure, configuration errors, unsupervised carrier network errors). Two implementations are proposed:
• multiple DFS traversals, each with different time-to-live TTL, using binary search to find the point where packet is lost. Complexity: log n
• smart in-band counter: counter is read and updated during packet processing, and counter value can be written to packet header field; proactively install one smart counter per switch port; two DFS traversals needed: first traversal will go back and forth once on new link, second traversal will detect the blackhole (link with counter of value 1).
• Critical node detection: check if a node is critical for connectivity; non-critical node may be removed for maintenance and energy conservation; cheaper than snapshot; only one DFS traversal with root. 
• Anycast: supports specification of multiple unknown destinations; it is extendable to specify service chains; useful to find an alternative path to the controller when link fails. Complexity: one DFS traversal 

What’s good about the approach in this paper:

• no new hardware or protocol features are required 
• keep states formally verifiable 
• some techniques are possibly extendable to other functions (e.g., using smart counter to infer network load). 

This work serves as the first step and more discussions on how to partition functionalities between data plane and control plane are encouraged.