# Enhancing Data Security Through VLSM Subnetting and TCP/IP Model in an ENT
## 1 Introduction  
Information and cyber security safeguard digital assets, data at-rest, in-transit, or in-use from adversaries to ensure confidentiality, integrity, and availability (CIA). While data security safeguards stored or electronically transmitted data from actions which may cause an adverse impact on essential functions [1, 2], information security safeguards information and information systems from unauthorised access, use, disclosure, disruption, modification, or destruction [3, 4, 5, 6]. The data and information at-rest, in-transit, or in-use can be securely transmitted from the source to destination using network principles and best practices relating to the updated TCP/IP model. Building and properly configuring protocols and networks securely from a best practice point-of-view, should reduce or mitigate the risks of cyber threats to organisations. Cybercrime and frauds by cybercriminals are on the rise leading to the disruption of websites, and momentary access loss to networks [7]. In 2023, ref. [8] reported breaches which affected 815 million residents according to the Indian Council of Medical Research. Data records of about 20 million persons held by 23 andMe. At Redcliffe Labs, more than 12 million medical records were exfiltrated, and at the UK Electoral Commission data of approximately 40 million voters were compromised. Network design and setupshould be in compliance with approved standards and best practices to avoid the risk of misconfiguration, which can render information and systems vulnerable to cyber threats. In large networks, VLSM together with Port (Network) Address Translation (PAT) can ensure the effective exchange of packets between different locations. PAT translates private addresses used within an internal network into a single public IP address visible on the internet, so that the IPv4 space is conserved, and the internal network structure is hidden from the internet [9]. For large enterprise networks, it may not be practical to have an all-cisco device network; thus, inclining towards OSPF [10,11] can be premeditated. EIGRP [12,13] is a Cisco proprietary protocol whereas OSPF is an open vendor protocol. Internet Protocol Security (IPSec) is a popular Virtual Private Network (VPN) protocol suite which applies authentication and encryption on the Internet Protocol (IP) in three classical communication scenarios: host-to-host, host-to-site, and site-to-site. IPSec creates a boundary between unprotected and protected interfaces, for a host or a network [14]. Ref. [14] recommend a security gateway to support the three communication scenarios, since, under certain circumstances, a security gateway acts as a host, whereby hosts support host-to-host and host-to-site. IPSec comprises the Authentication Header (AH) and Encrypted Secured Payload (ESP) protocol. The AH of IPSec ensures the integrity and authenticity of IP packets by calculating and verifying cryptographic hashes of packet contents. ESP encrypts the payload to keep data confidential, and it also calculates and verifies hashes to ensure data integrity and authenticity. The hierarchical network design [15,16] of our ENT relates to Cisco Architecture Design (CAD) covering wired and wireless hosts such as a DNS/HTTP server, computers, mobile devices, switches, and routers. The ENT design can increase in scalability, redundancy, bandwidth, access layer, and fine-tuning routing protocols. The data and information reach their destination through the routing protocols in the network layer of the TCP/IP model with the assigned single IP address. The strategy for converting the subnet mask will be presented, applied to the ENT designed network, and simulated with Cisco Packet Tracer. To the best of our knowledge, there is no current research that combines VLSM subnetting [17,18], performance, and [19,20] into a boilerplate that can be applicable to the teaching of networking. This work holds great potential as it may be expanded into SCADA systems [21], IoT [22], and the Cloud [22].