# Practical Implementation of a Blockchain-Enabled SDN for Large-Scale Infrastructure Networks
## 1 Introduction
The proposed solution is relevant in the context of the evolving technology landscape and the demands of modern network environments for several reasons:  
* It is using well-established technologies for large-scale systems, namely Software-Defined Networking and blockchain;
* It encourages the collaboration between ISPs and offers a technical solution for the formation of heterogeneous ISP federations;
* ISP federations bring benefits to customers, improving their internet experience and access to services;
* It provides an architectural framework for improved network scalability, security and reliability;
* It can reduce energy consumption and optimize resource allocation by integrating blockchain nodes directly on SDN controllers. Figure 1: SDN structure with integrated blockchain nodes and regular SDN structure. Novel concepts are introduced in the current research to integrate blockchain and SDN technologies on large-scale infrastructure networks. The main goal of the article is the integration of blockchain technology into SDN infrastructures, mainly using SDN controllers as blockchain nodes across a federation of ISPs. Existing solutions in the state of the art do not offer a complete way of integrating the two technologies and are focused mainly on specific architectural or functional aspects (for example, using blockchain as a distributed encrypted archive). By using existing SDN controllers as blockchain nodes, organizations can optimize resource utilization, reducing the need for additional hardware. SDN controllers typically have sufficient computational resources and storage capacity to accommodate blockchain node functionalities. The proposed use case--using SDN controllers as blockchain nodes across a federation of ISPs--also highlights the business aspects by providing operational efficiency and scalability. The main originality aspects of the current article and the complexity of the proposed solution are highlighted below:  
* This is one of the first integrations, to the best of the authors' knowledge, between SDN and blockchain, where SDN controllers are used as blockchain nodes at the ISPs' level, using emulators and physical devices;
* An architectural solution for interconnecting heterogeneous ISPs in an ISP federation;
* This work contains, to the best of the authors' knowledge, the first Pox SDN controller extensions with blockchain features;
* In order to manage the subject of integrating the two technologies from a complete architectural view, without focusing only on specific aspects, a novel concept was introduced: vISP (virtual ISP) that allows the creation of a federation of ISPs and abstracts the complexity of interconnecting heterogeneous ISPs;
* With the introduction of the concept of virtual ISP over the ISP federation, the multitude of ISPs can be treated uniformly, and the problem of ISP heterogeneity can be addressed and solved. In this regard, a virtual ISP will consist of ISPs that choose to participate in the blockchain integration over their SDN infrastructures and will have the required high-level architecture role needed to treat uniformly heterogenous ISPs;
* The complexity of current work derives also from the integration of multiple tools, technologies and programming languages to create the research and test environment. The Mininet network emulator [1] was used to create the needed network topologies in the testing setup. Geth was used to create the blockchain network. The source code of the POX SDN controller was modified to integrate the Geth functionality and thus create the SDN-blockchain integration at the technical level. Python programming language and Linux bash scripting language were utilized to achieve this integration. Wireshark was used as a network monitoring tool to validate the implementation and test blockchain traffic being transmitted from the POX SDN controller customization. The remainder of the article is structured as follows: Section 2 provides work related to the current research. Section 3 describes the system design and architecture.