SSH (Secure Shell) is a cryptographic network protocol that enables secure remote management and operation of network devices, including routers and switches. SSH encrypts traffic, making it more secure than alternatives like Telnet, which sends data in plaintext. The document states:
"SSH (Secure Shell) is the recommended protocol for secure, interactive remote management of network devices. It provides a secure channel over an unsecured network by encrypting the traffic between the administrator's workstation and the managed device."

An on-path attack (formerly known as a man-in-the-middle (MITM) attack) involves intercepting and potentially altering communications between two parties without their knowledge. This can be done via techniques like ARP poisoning, rogue access points, or SSL stripping.
Breakdown of Options:
A). Self-signed certificate - These are untrusted SSL certificates but do not intercept traffic.
B). VLAN hopping - VLAN hopping exploits VLAN misconfigurations but does not necessarily intercept communications.
C). On-path attack - Correct answer. This intercepts and modifies traffic between two endpoints.
D). Phishing - Phishing tricks users into revealing credentials rather than intercepting network traffic.
Reference:
CompTIA Network+ (N10-009) Official Study Guide - Domain 3.2: Explain common security concepts.
NIST SP 800-115: Guide to Security Testing and Assessments

When a DHCP server is installed and not enough IP addresses are provisioned, users may start experiencing network outages once the available IP addresses are exhausted. DHCP servers assign IP addresses to devices on the network, and if the pool of addresses is too small, new devices or those renewing their lease may fail to obtain an IP address, resulting in network connectivity issues.References:CompTIA Network+ study materials.

X.509 certificates are most commonly associated with Public Key Infrastructure (PKI). These certificates are used for a variety of security functions, including digital signatures, encryption, and authentication.
* PKI: X.509 certificates are a fundamental component of PKI, used to manage encryption keys and authenticate users and devices.
* Digital Certificates: They are used to establish secure communications over networks, such as SSL/TLS for websites and secure email communication.
* Authentication and Encryption: X.509 certificates provide the means to securely exchange keys and verify identities in various applications, ensuring data integrity and confidentiality.
Network References:
* CompTIA Network+ N10-007 Official Certification Guide: Covers PKI and the role of X.509 certificates in network security.
* Cisco Networking Academy: Provides training on PKI, certificates, and secure communications.
* Network+ Certification All-in-One Exam Guide: Explains PKI, X.509 certificates, and their applications in securing network communications.

When dealing with troubleshooting and change management, the plan of action outlines the steps, risks, and mitigation strategies. A change advisory board (CAB) uses this documented plan to decide whether to approve the change.
A). Identify the problem is the first step in troubleshooting, not decision-making for CAB.
B). Develop a theory is diagnostic work, not planning.
C). Test the theory confirms causes but doesn't provide actionable planning information.
References (CompTIA Network+ N10-009):
Domain: Network Operations - Change management, troubleshooting methodology, CAB processes.