Reducing State of OpenFlow Switches in Mobile Core Networks by Flow Rule Aggregation
Ramin Khalili, Wint Yi Poe, Zoran Despotovic, Artur Hecker · 2016
While bringing many advantages, Software-Defined Networking (SDN) is accompanied by potential scalability issues that should be considered in the design of SDN-based networks. Specifically, SDN hardware switches based on Ternary Content-Addressable Memory (TCAM) can only store a few thousands of rules, imposing thus severe limits on the number of flows they can serve/process. Current proposals to deal with this problem mainly focus on optimal placement of flows that complies with the given constraints on TCAM size. We argue in this paper that flow routing not only should be but also can be independent of TCAM size constraints. We introduce two flow rule aggregation algorithms: One performs the "per-outport'' aggregation of the paths between access nodes in the network. It is optimal in that it holds the flow table sizes at the minimum, but has a drawback that it produces long identifiers of the path endpoints (access nodes), which cannot fit the IP address size. The other algorithm is its approximation under the constraint that the generated identifiers fit the limit imposed by the addressing scheme (e.g., IPv4). We study the performance of our algorithms analytically and through a set of experiments. While the optimal solution always keeps the flow table sizes at the minimum, we show that the approximate algorithm reduces the flow table sizes by a factor of 2 to 10 compared to the state of the art solution, under a reasonable constraint on the address length (e.g., 32 bits in case of IPv4).