# A Survey on Efforts to Evolve the Control Plane of Inter-Domain Routing
## 6 Further Discussion and Lessons Learned
### SDN as an Enabling Technology  
One of the major features of the BGP is the scalability of the protocol due to its fully-distributed nature. The size-effect of distributed control of the BGP is causing the protocol \"chatitness\" [19] and the long convergence time [22], since every BGP speaker has to generate the global view of the network state to make decisions about routing. The centralization of inter-domain routing control has the potential to mitigate the BGP issues [7; 35; 36]. A bird's eye view of the centralized solution has the potential to identify misconfiguration, avoid route leaks, address the satisfaction and dissatisfaction among ASs [31] and understand and perform troubleshooting; all sorts of undesired network behavior will be exposed to the centralized control. With SDN technologies, the consistency of the network state is encouraged by the principle of logical centralization [52]. The inter-domain routing centralization has the potential to benefit the application of traffic engineering techniques, enforcement of routing policies, network troubleshooting and other desirable features. For example, the proposal of iSDX [68] uses the SDN centralized control in an IXP to allow the creation of more flexible forwarding policies, the reduction of the forwarding table size of OpenFlow devices used by the IXP participants and the end-to-end enforcing of QoS. The adoption of SDN technologies has the potential to solve the management decentralization problem of the traditional network, as discussed in [97]. Other previous proposals that use exclusively traditional network technologies [38; 59] required extensions for the BGP or a brand new network protocol to make them operational. This results in a difficult scenario that is not easy to deploy or manage for ASs because of CAPEX, OPEX, security and reliability concerns. New network services can emerge if the current inter-domain routing system allows the evolution of the routing control plane. The traditional network mostly applies the decentralization of the routing decision, and with the advent of SDN concepts, the logical centralization of the routing control plane may enable inter-domain routing evolution. Thereby, a good question to pose regarding SDN is the following: Why have SDN technologies not yet changed the inter-domain landscape? First of all, it is worth noting that the SDN paradigm is a brand new approach to design networks (although it inherits ideas from other approaches [43]), which is different from the traditional network that has been the main paradigm to construct networks since the Internet's inception. Thereby, the technologies that instantiate SDN concepts are in their early stages, and as they are not mature technologies, wide adoption is not expected. The most successful SDN technology is the OpenFlow protocol. This protocol has some hindrance regarding memory and signaling utilization [98] because OpenFlow switches usually use Ternary Content Addressable Memory (TCAM) as the main memory to match a flow. That type of memory is very fast, however having the drawback of being expensive with a high energy consumption. Therefore, the fine-grained OpenFlow rules can represent a cumbersome inter-domain environment where the number of prefixes (or flows) is tremendously high [62]. Flow management is almost mandatory for the real deployment of the OpenFlow protocol in inter-domain routing, and that problem can be understood as an extension of the rule placement problem inside OpenFlow networks. A detailed survey about flow management can be seen in the work of [PERSON] et al. [45]. Another drawback of the OpenFlow networks is the reliability between controllers and the data plane elements (OpenFlow switches). Once the control and data plane is decoupled, when the control becomes unavailable, the forwarding elements may not continue to work appropriately.