# Practical Implementation of a Blockchain-Enabled SDN for Large-Scale Infrastructure Networks
## 3 System Proposal
The data marked as public are stored in the blockchain without any other additional intervention. The blockchain can function as a secure platform for sharing data marked with this scope, besides maintaining all the information from all the providers safe, both public and private. The blockchain operation is maintained through the active involvement of every ISP in the federation, by operating a node (at least). In Figure 3, the interaction between the service providers and the integrated permissioned blockchain can be observed. The service providers have several options available for integrating the blockchain. These alternatives are related to the communication methodologies established between the service provider and the blockchain. The blockchain integration will manage the data processing tasks essential for storing information on the blockchain platform. The ISPs maintain permissioned blockchain nodes in their SDN networks using SDN controllers. The permissioned blockchain stores common information (public data) of interest for all the service providers in the federation, but it also stores private information--data that are of interest and that should be available only for the ISP that committed the data to the blockchain, as already mentioned. Using private key sets, every ISP is able to store private data--data strictly related to its own network--on the permissioned blockchain. In this way, the data are encrypted when stored on the blockchain and could be decrypted only by having the keys. Thus, every ISP can have a private section of data on the federation's permissioned blockchain to use as they prefer. Leveraging the federation blockchain by  
Figure 3: Federation of ISPs that integrate blockchain over their SDN networks. Figure 2: vISP interaction with other ISPs. integrating it over the SDN network not only enhances security but also enhances the other properties of the blockchain due to the extended surface of the blockchain. As an increasing number of ISPs adhere to the federation and integrate the blockchain, the area of the blockchain expands, resulting in enhanced security of other intrinsic attributes of the blockchain. Blockchain technology can be extended within the platform over the service providers' SDN networks that adhere to the federation. This process can be carried out by extending the SDN network devices' functionality with a part that handles blockchain functionality. As it was previously mentioned, the blockchain nodes (full/complete) offer a detailed perspective of the information stored in the blockchain. The SDN network devices, according to their capacity, can take over blockchain node functionality. The main coordinator for an SDN network is the SDN controller. This network device controls and ensures the good functioning of the whole SDN network having control over all the network devices. Thus, such a device would be appropriate to take over the functionality of a full blockchain node within the integrated blockchain extended over all the SDN networks from the federation. In this manner, the SDN controller also has control over the data that will represent the transactions stored in the distributed ledger and, implicitly, control over the new integrated part of functionality. Due to redundancy considerations and enhanced security requirements, the centralized control component of the SDN network can be improved through the adoption of distributed controllers, as indicated by existing research in this domain [11,13] and as survey articles on SDN technology also demonstrate interest over time, as indicated by the research findings [22, 23, 24]. Taking inspiration from the distributed manner of the blockchain, such an implementation would increase the covering area of the SDN network and would also benefit the proposed model. By taking the capability of a blockchain full node also, the controllers could increase the covering area of the blockchain integrated within the federation.