# A Survey on Efforts to Evolve the Control Plane of Inter-Domain Routing
## 5 Classification of Efforts for Evolving the Control Plane
### Efforts to Evolve the Control Plane of Inter-Domain Routing
#### 5.2.3 Inter-Domain Communication
It tackles the lack of information when a BGP session was reset or shutdown. Thus, the solution adds a short text message as part of the notification message of the BGP [6]. The purpose of that message is to notify operators about the event that caused the BGP closure. RouteFlow [79] controls and configures flows of OpenFlow switches using Quagga [71] as the main engine. RouteFlow becomes a proxy for the OpenFlow controller, where all the network logic follows traditional network protocols with inter-domain routing executing the BGP protocol. Furthermore, RouteFlow provides virtualized IP routing services over OpenFlow-enabled hardware, with the main idea of the proposed architecture adopting a west/eastbound interface to make a deeper integration of the routing engines of an ISP and its customers. As recent surveys indicate, there is not yet a standard west/eastbound SDN interface to exchange network control information between different SDN controllers [80; 39; 85]. Thereby, to allow the communication between SDN controllers in the inter-domain ecosystem, the authors in [80] proposed an interface for SDN to exchange reachability and topology information, the WE-Bridge [80]. The goals were to present a peer-to-peer mechanism that has to be resilient, secure and exchange network control information for ASs. WE-Bridge was used by RCS [61] and SDI [62] to exchange control information between SDN controllers. To exchange routing information between SDN domains (a domain that deploys SDN technologies), the Inter-SDN Routing Component [81] was proposed to tackle the problem of integration between the different control planes. Using TCP connections, the new exchange mechanism is inspired by the BGP and incorporates messages similar to the BGP (OPEN, UPDATE, KEEPALIVE and NOTIFICATION), uses RIBs (RIB-In, Local RIB, RIB-Out) and simplifies the route selection decision process. The Inter-SDN claims that the way to solve inter-domain issues is through architectural abstraction (SDN applications) and extensibility properties (the network programmability). Application-Layer Traffic Optimization (ALTO) [82] (defined in RFC 7285) is the most detailed specification for a standardization of the east/westbound interface for SDN controllers. It provides a network information service with the goal of exporting resources and parameters to network applications. ALTO is based on abstract maps of a network that simplify the state of a network and the applications that can effectively use them. Summary: Traditional network approaches for inter-domain communications focus on adding new capabilities or modifications to the BGP's messages. However, those approaches require a long cycle (months or years) of development until they reach the production environment. The SDN and traditional network have one point in common: those initiatives tackle the challenge of managing a huge number of network devices that requires coordination among multiple control planes. In fact, to overcome BGP control plane limitations for inter-domain communication, SDN approaches seek an integration with BGP and coordination between SDN controllers. Additionally, SDN network applications require complex network information that is hidden through inter-domain routing to allow the propriety execution of optimization algorithms in the network [86].