Protect the infrastructure.
Protect the information.

Identify threats and attacks

Threats include malware such as viruses, worms, and ransomware; social engineering and phishing; denial-of-service; password attacks; interception; and exploitation of unpatched vulnerabilities. Internal risks include lost devices, accidental disclosure, misconfiguration, and malicious insiders. Assess both the likelihood of an attack and its potential impact.

Secure network devices

Change default credentials, use strong secrets, restrict management access, prefer SSH over Telnet, keep software updated, disable unused services and ports, and use secure management networks. Apply least privilege and use logging and monitoring to detect suspicious behavior. Physical access controls protect equipment from direct tampering.

Layer network security controls

Firewalls filter traffic according to policy. Access control lists (ACLs) permit or deny traffic based on packet attributes. IOS evaluates ACL entries from top to bottom and applies the first matching entry; if no entry matches, an implicit deny blocks the packet. Put specific exceptions before broad permits, and verify the ACL is applied in the intended direction on the correct interface. Intrusion prevention systems (IPS) inspect traffic for malicious patterns. VPNs protect traffic across untrusted networks. Defense in depth combines multiple controls rather than relying on a single security product.

Classify security impacts and interception attacks

The CIA triad describes three core security objectives. Confidentiality prevents unauthorized disclosure of information; integrity protects information from unauthorized alteration; availability ensures authorized users can access systems and data when needed. One incident can affect more than one objective: data theft affects confidentiality, record tampering affects integrity, and a denial-of-service attack affects availability.

A man-in-the-middle (MITM) attacker positions themselves between communicating endpoints to intercept or modify traffic. Use authenticated encryption such as TLS, validate server certificates, and do not bypass certificate warnings. A VPN can protect traffic across an untrusted access network, but end-to-end application authentication remains important.

Protect endpoints and preserve recovery options

Keep operating systems, applications, and network-device software patched. Endpoint protection and endpoint detection and response (EDR) help identify malicious activity on individual devices. Network access control (NAC) can restrict access based on device identity or security posture. Use physical controls to protect equipment and management interfaces, and place public-facing services in appropriately segmented DMZ networks rather than exposing trusted internal systems directly.

Back up device configurations and required software images using authenticated, protected storage. Keep recovery copies separate from the systems they protect, restrict who can alter them, and test restoration. Cisco AutoSecure can help apply baseline hardening on supported IOS platforms, but generated changes must be reviewed for the device's role and operational requirements.