CNSP Exam Dumps : Certified Network Security Practitioner (CNSP)

ICMP (Internet Control Message Protocol), per RFC 792, handles diagnostics (e.g., ping) and errors in IP networks. It’s exploitable in:

A. Ping of Death:

Method: Sends oversized ICMP Echo Request packets (>65,535 bytes) via fragmentation. Reassembly overflows buffers, crashing older systems (e.g., Windows 95).

Fix: Modern OSes cap packet size (e.g., ping -s 65500).

B. Smurf Attack:

Method: Spoofs ICMP Echo Requests to a network’s broadcast address (e.g., 192.168.255.255). All hosts reply, flooding the victim.

Amplification: 100 hosts = 100x traffic.

C. ICMP Flooding:

Method: Overwhelms a target with ICMP Echo Requests (e.g., ping -f), consuming bandwidth/CPU.

Variant: BlackNurse attack targets firewalls.

Technical Details:

ICMP Type 8 (Echo Request), Type 0 (Echo Reply) are key.

Mitigation: Rate-limit ICMP, disable broadcasts (e.g., no ip directed-broadcast).

Security Implications:ICMP attacks are DoS vectors. CNSP likely teaches filtering (e.g., iptables -p icmp -j DROP) balanced with diagnostics need.

Why other options are incorrect:

A, B, C individually:All are ICMP-based; D is comprehensive.

Real-World Context:Smurf attacks peaked in the 1990s; modern routers block them by default.References:CNSP Official Study Guide (Network Attacks); RFC 792 (ICMP).

TCP (Transmission Control Protocol) and UDP (User Datagram Protocol) port numbers are defined by a 16-bit field in their packet headers, as specified in RFC 793 (TCP) and RFC 768 (UDP). A 16-bit integer ranges from 0 to 65,535, yielding a total of 65,536 possible ports (2^16). However,port 0is universally reserved across both protocols and is not considered "usable" for standard network communication. According to the Internet Assigned Numbers Authority (IANA), port 0 is designated for special purposes, such as indicating an invalid or dynamic port assignment in some systems (e.g., when a client requests an ephemeral port). In practice, operating systems and applications avoid binding to port 0 for listening services, and it’s often used in error conditions or as a placeholder in protocol implementations (e.g., socket programming).

Thus, theusable port rangespans from 1 to 65,535, totaling 65,535 ports. These ports are categorized by IANA into:

Well-Known Ports (0–1023):Reserved for system services (e.g., HTTP on 80/TCP). Note that 0 is still reserved within this range.

Registered Ports (1024–49151):Assigned to user applications.

Dynamic/Ephemeral Ports (49152–65535):Used temporarily by clients.

From a security perspective, understanding the usable port count is critical for firewall configuration, port scanning (e.g., with Nmap), and detecting anomalies (e.g., services binding to unexpected ports). Misconfiguring a system to use port 0 could lead to protocol errors or expose vulnerabilities, though it’s rare. The CNSP curriculum likely emphasizes this distinction to ensure practitioners can accurately scope network security assessments.

Why other options are incorrect:

A. 65536:This reflects the total number of possible ports (0–65535), but it includes the reserved port 0, which isn’t usable for typical TCP/UDP communication. In security contexts, including port 0 in a count could lead to misconfigured rules or scanning errors.

C. 63535:This is an arbitrary number with no basis in the 16-bit port structure. It might stem from a typo or misunderstanding (e.g., subtracting 2000 from 65535 incorrectly), but it’s invalid.

D. 65335:Similarly, this lacks grounding in protocol standards. It could be a miscalculation (e.g., subtracting 200 from 65535), but it doesn’t align with TCP/UDP specifications.

Real-World Context:In penetration testing, tools like Nmap scan ports 1–65535 by default, excluding 0 unless explicitly specified (e.g., -p0-65535), reinforcing that 65,535 is the practical usable count.References:CNSP Official Study Guide (Network Protocols and Ports); RFC 793 (TCP), RFC 768 (UDP), IANA Service Name and Transport Protocol Port Number Registry.

Online attacks require real-time interaction with a target system (e.g., a login interface), whereas offline attacks occur without direct system interaction, typically after obtaining data like password hashes. A rainbow table attack is an offline method that uses precomputed tables of hash values to reverse-engineer passwords from stolen hash databases, distinguishing it from the other options, which are online.

Why B is correct:Rainbow table attacks are performed offline after an attacker has already acquired a hash (e.g., from a compromised database). The attacker matches the hash against precomputed tables to find the plaintext password, requiring no interaction with the target system during the attack. CNSP classifies this as an offline password recovery technique.

Why other options are incorrect:

A:Brute force attacks involve repeatedly submitting password guesses to a live system (e.g., via SSH or a web login), making it an online attack.

C:Password spraying attacks test a few common passwords across many accounts on a live system, also an online attack aimed at avoiding lockouts.

D:Phishing attacks trick users into submitting credentials through fake interfaces (e.g., emails or websites), requiring real-time interaction and thus classified as online.

References:CNSP "Password Attack Methodologies" (Section on Online vs. Offline Attacks) defines rainbow table attacks as offline and contrasts them with online methods like brute force and phishing.