Compare Single-Mode Fiber (SMF) and Multi-Mode Fiber (MMF) across core size, light source, distance, and dispersion.

Single-Mode Fiber (SMF): small core (8-10 microns), laser light source, supports long distances (up to 40+ km), low attenuation, zero modal dispersion. Multi-Mode Fiber (MMF): larger core (50 or 62.5 microns), LED/VCSEL light source, shorter distances (up to 300-500 meters), lower transceivers cost, but limited by modal dispersion.

What port numbers and transport protocols are used by FTP, SSH, Telnet, SFTP, TFTP, and RDP?

FTP: TCP 20 (data) & TCP 21 (control); SSH: TCP 22; Telnet: TCP 23; SFTP: TCP 22 (SSH File Transfer); TFTP: UDP 69 (Trivial FTP); RDP: TCP 3389 (Remote Desktop Protocol).

Why is a DHCP Relay Agent (IP Helper) required when clients and the DHCP server reside in different subnets?

DHCP Discover packets are Layer 2 broadcast frames, and standard Layer 3 routers do not forward broadcasts across subnet boundaries. A DHCP Relay Agent (configured with `ip helper-address` on Cisco routers) intercepts client broadcasts, converts them into unicast IP packets directed to the DHCP server IP, and forwards them across subnets.

What are the four steps of the DHCP IP address allocation process (DORA)?

1. Discover: Client broadcasts DHCPDISCOVER looking for a DHCP server (UDP 67, 255.255.255.255); 2. Offer: DHCP server responds with DHCPOFFER proposing an IP address, mask, lease time, and default gateway; 3. Request: Client broadcasts DHCPREQUEST requesting to lease the offered IP; 4. Acknowledge: Server sends DHCPACK confirming the lease.

Compare the 2.4 GHz and 5 GHz wireless frequency bands regarding channels, range, and attenuation.

2.4 GHz: longer physical range, penetrates solid walls better (lower attenuation), but has high interference and only 3 non-overlapping 20 MHz channels (1, 6, 11). 5 GHz: shorter physical range and higher wall attenuation, but offers higher data rates and up to 24 non-overlapping 20 MHz channels with substantially less interference.

Compare Power over Ethernet (PoE) standards: 802.3af (PoE), 802.3at (PoE+), and 802.3bt (PoE++ Type 4) regarding maximum power delivered.

802.3af (PoE): provides up to 15.4 W at the switch port (12.95 W delivered to device); powers basic VoIP phones and sensors. 802.3at (PoE+): provides up to 30 W at switch port (25.5 W delivered); powers PTZ cameras and 802.11ac APs. 802.3bt (PoE++ Type 4): provides up to 90-100 W (71.3 W delivered across all 4 copper pairs); powers digital signage and thin clients.

What are the wire color pinouts for TIA/EIA-568A and TIA/EIA-568B cabling standards?

568A: 1-Green/White, 2-Green, 3-Orange/White, 4-Blue, 5-Blue/White, 6-Orange, 7-Brown/White, 8-Brown. 568B: 1-Orange/White, 2-Orange, 3-Green/White, 4-Blue, 5-Blue/White, 6-Green, 7-Brown/White, 8-Brown. Straight-through uses same standard on both ends; crossover uses 568A on one end and 568B on the other.

Explain how traceroute / tracert identifies each router hop along a network path.

Traceroute sends packets (ICMP Echo on Windows, UDP on Linux) with an incrementing Time-to-Live (TTL) field starting at TTL=1. When a router receives a packet with TTL=1, it decrements TTL to 0, drops the packet, and returns an ICMP Type 11 (Time Exceeded) message to the source, revealing the router's IP address and round-trip time.

What are the core DNS record types: A, AAAA, CNAME, MX, PTR, TXT, and SOA?

A: maps hostname to IPv4 address; AAAA: maps hostname to IPv6 address; CNAME: canonical name (alias for another domain name); MX: mail exchange server (with priority number); PTR: reverse DNS mapping IP address to hostname; TXT: human/machine-readable text used for SPF, DKIM, and DMARC verification; SOA: Start of Authority (zone serial number, refresh intervals).

Compare Twisted-Pair Ethernet cable categories: Cat 5e, Cat 6, Cat 6a, and Cat 7 across bandwidth and maximum distance.

Cat 5e: 1 Gbps up to 100 meters, 100 MHz bandwidth. Cat 6: 1 Gbps up to 100 meters (or 10 Gbps up to 55 meters in low-crosstalk environments), 250 MHz bandwidth. Cat 6a: 10 Gbps up to 100 meters, 500 MHz bandwidth (improved alien crosstalk shielding). Cat 7: 10 Gbps up to 100 meters, 600 MHz bandwidth (individually shielded pairs).

What is Quality of Service (QoS), and how do DSCP and CoS prioritize latency-sensitive traffic?

QoS manages network congestion to guarantee bandwidth and minimize latency, jitter, and packet loss for mission-critical traffic. CoS (Class of Service) operates at Layer 2 using a 3-bit Priority Code Point (PCP) in the 802.1Q header. DSCP (Differentiated Services Code Point) operates at Layer 3 using a 6-bit field in the IPv4 DiffServ header (e.g., EF / Expedited Forwarding for VoIP).

Given the IP address 192.168.50.100/27, determine the Subnet Mask, Network Address, First Usable Host, Last Usable Host, and Broadcast Address.

Subnet Mask: 255.255.255.224 (/27 = 32 - 27 = 5 host bits, block size = 2^5 = 32). Subnet multiples: 0, 32, 64, 96, 128. Host .100 falls in subnet .96. Network Address: 192.168.50.96; First Usable: 192.168.50.97; Last Usable: 192.168.50.126; Broadcast Address: 192.168.50.127.

Define Latency, Jitter, Packet Loss, and Attenuation in transmission media.

Latency: total time required for a packet to travel from source to destination. Jitter: variation or fluctuation in packet arrival latency (highly disruptive to real-time voice and video). Packet Loss: percentage of sent packets that fail to reach the destination due to congestion or corruption. Attenuation: gradual loss of electrical or optical signal strength over transmission distance.

Explain the step-by-step DNS resolution process for a client querying a new external domain name.

1. Client checks local DNS cache and hosts file; 2. Client queries local recursive DNS resolver; 3. If cache miss, recursive resolver queries Root Nameserver ('.'); 4. Root server refers resolver to Top-Level Domain (TLD) nameserver (e.g., '.com'); 5. TLD server refers resolver to authoritative nameserver for domain; 6. Authoritative server returns IP address; 7. Resolver caches answer and returns it to client.

What port numbers and transport protocols are used by HTTP, HTTPS, DNS, DHCP, SMTP, POP3, and IMAP?

HTTP: TCP 80; HTTPS: TCP 443; DNS: UDP/TCP 53; DHCP: UDP 67 (server) & UDP 68 (client); SMTP: TCP 25 (relay) / 587 (submission); POP3: TCP 110 (unencrypted) / 995 (POP3S); IMAP: TCP 143 (unencrypted) / 993 (IMAPS).

How does Address Resolution Protocol (ARP) operate, and what is ARP Spoofing / Poisoning?

ARP resolves a known Layer 3 IPv4 address to an unknown Layer 2 MAC address. A host broadcasts an ARP Request ('Who has 192.168.1.1? Tell MAC A'); target responds with a unicast ARP Reply. ARP Spoofing occurs when an attacker broadcasts fraudulent ARP replies linking the attacker's MAC address to the default gateway's IP, intercepting subnet traffic (MitM attack).

Explain the difference between Static NAT, Dynamic NAT, and Port Address Translation (PAT / NAT Overload).

Static NAT: one-to-one permanent mapping of an internal private IP to an external public IP (used for inbound hosting of web/mail servers). Dynamic NAT: many-to-many temporary mapping from a registered pool of public IPs. PAT (NAT Overload): maps multiple private internal IPs to a single public IP address by assigning unique Layer 4 source port numbers.

What are the primary hardware devices and protocols associated with OSI Layer 1 (Physical) versus Layer 2 (Data Link)?

Layer 1 (Physical): Hubs, repeaters, network cables (Cat6, fiber optic), wireless transceivers; handles electrical voltages, bits, and radio frequencies. Layer 2 (Data Link): Network Interface Cards (NICs), Layer 2 switches, bridges; uses 48-bit MAC addresses (EUI-48), Ethernet (802.3), Wi-Fi frames (802.11), and Frame Check Sequence (FCS/CRC).

What is the function of IEEE 802.1Q in Virtual Local Area Networks (VLANs), and what is a Native VLAN?

802.1Q is the industry standard for VLAN trunking. It inserts a 4-byte tag into the Ethernet frame header containing a 12-bit VLAN ID (VID, allowing 4,096 VLANs). The Native VLAN is the single VLAN designated on an 802.1Q trunk port whose frames are transmitted across the trunk untagged (default VLAN 1).

What are the mathematical formulas for calculating the number of subnets and usable host IP addresses per subnet in IPv4?

Number of subnets = 2^s, where s is the number of borrowed subnet bits. Number of usable hosts per subnet = 2^h - 2, where h is the number of remaining host bits (subtracting 2 for the Network Address and the Broadcast Address). For example, /26 has 6 host bits: 2^6 - 2 = 62 usable hosts.

Compare the IEEE Wi-Fi standards: 802.11b, 802.11a, 802.11g, 802.11n (Wi-Fi 4), 802.11ac (Wi-Fi 5), and 802.11ax (Wi-Fi 6).

802.11b: 2.4 GHz, up to 11 Mbps; 802.11a: 5 GHz, up to 54 Mbps; 802.11g: 2.4 GHz, up to 54 Mbps; 802.11n (Wi-Fi 4): 2.4 and 5 GHz, up to 600 Mbps (introduced MIMO); 802.11ac (Wi-Fi 5): 5 GHz only, up to 6.9 Gbps (introduced MU-MIMO); 802.11ax (Wi-Fi 6/6E): 2.4, 5, and 6 GHz, up to 9.6 Gbps (introduced OFDMA and BSS coloring).

Compare Star, Mesh, and Bus network topologies regarding fault tolerance and single points of failure.

Star: all nodes connect to a central switch/hub; failure of a cable affects only one host, but central switch failure collapses the network. Full Mesh: every node connects to every other node (n*(n-1)/2 links); maximum fault tolerance and redundancy, but highest cabling and port costs. Bus: all nodes share a single trunk cable; breaks in cable disrupt the entire bus.

What are the structural rules for compressing an IPv6 address, and what does 2001:0db8:0000:0000:0000:0000:1428:57ab compress to?

Rules: 1. Omit leading zeros in any 16-bit hextet (e.g., 0db8 becomes db8); 2. Replace one contiguous sequence of all-zero hextets with a double colon '::' (can only be done once per address to avoid ambiguity). The address compresses to: 2001:db8::1428:57ab.

What port numbers and transport protocols are used by SNMP, LDAP, LDAPS, NTP, SMB, and Syslog?

SNMP: UDP 161 (queries) & UDP 162 (traps); LDAP: TCP/UDP 389; LDAPS: TCP 636; NTP: UDP 123 (Network Time Protocol); SMB: TCP 445; Syslog: UDP 514 (default) or TCP 6514 (Syslog over TLS).

What is Link Aggregation (IEEE 802.3ad / 802.1AX LACP), and what are its benefits?

Link Aggregation combines multiple physical Ethernet links between two switches into a single logical high-bandwidth channel (EtherChannel/Port Channel). Benefits: multiplies aggregate bandwidth, provides automated load balancing across links, and provides transparent link failover without triggering Spanning Tree recalculation.

Compare Router-on-a-Stick and Layer 3 Switch implementations for Inter-VLAN Routing.

Router-on-a-Stick: uses a single physical router interface connected to a switch trunk port, divided into logical subinterfaces for each VLAN (limited by router interface bandwidth). Layer 3 Switch: routes traffic between VLANs internally using Switch Virtual Interfaces (SVIs) and dedicated ASIC hardware, providing line-rate wire-speed routing with significantly lower latency.

Compare OSI Layer 3 (Network) and Layer 4 (Transport) responsibilities and protocols.

Layer 3 (Network): Path determination, logical addressing, and packet forwarding across network boundaries (IPv4, IPv6, ICMP, IPsec, routers). Layer 4 (Transport): End-to-end host communication, port-level multiplexing, segmentation, and reliability. TCP provides connection-oriented, reliable, sequenced delivery with flow control; UDP provides connectionless, best-effort datagram delivery.

Compare SNMPv1/v2c with SNMPv3 regarding security and cryptographic capabilities.

SNMPv1 and SNMPv2c transmit community strings (passwords) in cleartext across the network, allowing eavesdropping and unauthorized configuration changes. SNMPv3 introduces User-based Security Model (USM) providing: Authentication (HMAC-MD5/SHA), Encryption/Privacy (AES/DES for payload confidentiality), and Message Integrity.

Why is Spanning Tree Protocol (STP 802.1D) essential in switched Ethernet networks, and what hazards does it prevent?

STP prevents Layer 2 switching loops in topologies with redundant physical switch uplinks. Without STP, Layer 2 broadcast frames circulate infinitely, causing Broadcast Storms, MAC database instability (MAC address flapping), and multiple duplicate frame copies delivered to end stations, crashing switch CPUs.

What are the three RFC 1918 Private IPv4 address ranges and the APIPA address block?

Class A Private: 10.0.0.0/8 (10.0.0.0 to 10.255.255.255); Class B Private: 172.16.0.0/12 (172.16.0.0 to 172.31.255.255); Class C Private: 192.168.0.0/16 (192.168.0.0 to 192.168.255.255). APIPA (Automatic Private IP Addressing): 169.254.0.0/16 (used when DHCP client cannot reach a DHCP server).

Compare WPA2 and WPA3 wireless security protocols, highlighting Simultaneous Authentication of Equals (SAE).

WPA2 uses AES-CCMP encryption and Pre-Shared Key (PSK), which is vulnerable to offline dictionary/brute-force attacks if an attacker captures the 4-way handshake. WPA3 replaces PSK with Simultaneous Authentication of Equals (SAE / Dragonfly handshake), providing forward secrecy and rendering offline dictionary attacks impossible even with weak passwords.

List the 7 layers of the OSI Model from Layer 7 to Layer 1 and their corresponding Protocol Data Units (PDUs).

Layer 7: Application (Data); Layer 6: Presentation (Data); Layer 5: Session (Data); Layer 4: Transport (Segments for TCP / Datagrams for UDP); Layer 3: Network (Packets); Layer 2: Data Link (Frames); Layer 1: Physical (Bits). Remember: All People Seem To Need Data Processing.

CompTIA A+ & Network+ — OSI Model (Layers 1–7), Common TCP/UDP Ports, Subnetting (CIDR), DNS, DHCP, VLANs & Wi-Fi (802.11)

Foundational IT and networking certification mastery for CompTIA A+ and Network+ covering the OSI 7-layer model PDUs and hardware, essential TCP/UDP ports, IPv4 CIDR subnetting, DNS hierarchy and records, DHCP DORA process, 802.1Q VLAN trunking, Wi-Fi 802.11 standards, and cabling standards.

Level: basic
Languages: en → en
Cards: 32
Markdown: CompTIA A+ & Network+ — OSI Model (Layers 1–7), Common TCP/UDP Ports, Subnetting (CIDR), DNS, DHCP, VLANs & Wi-Fi (802.11) (.md)

Flashcards (32)

#	Front (Term / Question)	Back (Definition / Answer)
1	Compare Single-Mode Fiber (SMF) and Multi-Mode Fiber (MMF) across core size, light source, distance, and dispersion.	Single-Mode Fiber (SMF): small core (8-10 microns), laser light source, supports long distances (up to 40+ km), low attenuation, zero modal dispersion. Multi-Mode Fiber (MMF): larger core (50 or 62.5 microns), LED/VCSEL light source, shorter distances (up to 300-500 meters), lower transceivers cost, but limited by modal dispersion.
2	What port numbers and transport protocols are used by FTP, SSH, Telnet, SFTP, TFTP, and RDP?	FTP: TCP 20 (data) & TCP 21 (control); SSH: TCP 22; Telnet: TCP 23; SFTP: TCP 22 (SSH File Transfer); TFTP: UDP 69 (Trivial FTP); RDP: TCP 3389 (Remote Desktop Protocol).
3	Why is a DHCP Relay Agent (IP Helper) required when clients and the DHCP server reside in different subnets?	DHCP Discover packets are Layer 2 broadcast frames, and standard Layer 3 routers do not forward broadcasts across subnet boundaries. A DHCP Relay Agent (configured with `ip helper-address` on Cisco routers) intercepts client broadcasts, converts them into unicast IP packets directed to the DHCP server IP, and forwards them across subnets.
4	What are the four steps of the DHCP IP address allocation process (DORA)?	1. Discover: Client broadcasts DHCPDISCOVER looking for a DHCP server (UDP 67, 255.255.255.255); 2. Offer: DHCP server responds with DHCPOFFER proposing an IP address, mask, lease time, and default gateway; 3. Request: Client broadcasts DHCPREQUEST requesting to lease the offered IP; 4. Acknowledge: Server sends DHCPACK confirming the lease.
5	Compare the 2.4 GHz and 5 GHz wireless frequency bands regarding channels, range, and attenuation.	2.4 GHz: longer physical range, penetrates solid walls better (lower attenuation), but has high interference and only 3 non-overlapping 20 MHz channels (1, 6, 11). 5 GHz: shorter physical range and higher wall attenuation, but offers higher data rates and up to 24 non-overlapping 20 MHz channels with substantially less interference.
6	Compare Power over Ethernet (PoE) standards: 802.3af (PoE), 802.3at (PoE+), and 802.3bt (PoE++ Type 4) regarding maximum power delivered.	802.3af (PoE): provides up to 15.4 W at the switch port (12.95 W delivered to device); powers basic VoIP phones and sensors. 802.3at (PoE+): provides up to 30 W at switch port (25.5 W delivered); powers PTZ cameras and 802.11ac APs. 802.3bt (PoE++ Type 4): provides up to 90-100 W (71.3 W delivered across all 4 copper pairs); powers digital signage and thin clients.
7	What are the wire color pinouts for TIA/EIA-568A and TIA/EIA-568B cabling standards?	568A: 1-Green/White, 2-Green, 3-Orange/White, 4-Blue, 5-Blue/White, 6-Orange, 7-Brown/White, 8-Brown. 568B: 1-Orange/White, 2-Orange, 3-Green/White, 4-Blue, 5-Blue/White, 6-Green, 7-Brown/White, 8-Brown. Straight-through uses same standard on both ends; crossover uses 568A on one end and 568B on the other.
8	Explain how traceroute / tracert identifies each router hop along a network path.	Traceroute sends packets (ICMP Echo on Windows, UDP on Linux) with an incrementing Time-to-Live (TTL) field starting at TTL=1. When a router receives a packet with TTL=1, it decrements TTL to 0, drops the packet, and returns an ICMP Type 11 (Time Exceeded) message to the source, revealing the router's IP address and round-trip time.
9	What are the core DNS record types: A, AAAA, CNAME, MX, PTR, TXT, and SOA?	A: maps hostname to IPv4 address; AAAA: maps hostname to IPv6 address; CNAME: canonical name (alias for another domain name); MX: mail exchange server (with priority number); PTR: reverse DNS mapping IP address to hostname; TXT: human/machine-readable text used for SPF, DKIM, and DMARC verification; SOA: Start of Authority (zone serial number, refresh intervals).
10	Compare Twisted-Pair Ethernet cable categories: Cat 5e, Cat 6, Cat 6a, and Cat 7 across bandwidth and maximum distance.	Cat 5e: 1 Gbps up to 100 meters, 100 MHz bandwidth. Cat 6: 1 Gbps up to 100 meters (or 10 Gbps up to 55 meters in low-crosstalk environments), 250 MHz bandwidth. Cat 6a: 10 Gbps up to 100 meters, 500 MHz bandwidth (improved alien crosstalk shielding). Cat 7: 10 Gbps up to 100 meters, 600 MHz bandwidth (individually shielded pairs).
11	What is Quality of Service (QoS), and how do DSCP and CoS prioritize latency-sensitive traffic?	QoS manages network congestion to guarantee bandwidth and minimize latency, jitter, and packet loss for mission-critical traffic. CoS (Class of Service) operates at Layer 2 using a 3-bit Priority Code Point (PCP) in the 802.1Q header. DSCP (Differentiated Services Code Point) operates at Layer 3 using a 6-bit field in the IPv4 DiffServ header (e.g., EF / Expedited Forwarding for VoIP).
12	Given the IP address 192.168.50.100/27, determine the Subnet Mask, Network Address, First Usable Host, Last Usable Host, and Broadcast Address.	Subnet Mask: 255.255.255.224 (/27 = 32 - 27 = 5 host bits, block size = 2^5 = 32). Subnet multiples: 0, 32, 64, 96, 128. Host .100 falls in subnet .96. Network Address: 192.168.50.96; First Usable: 192.168.50.97; Last Usable: 192.168.50.126; Broadcast Address: 192.168.50.127.
13	Define Latency, Jitter, Packet Loss, and Attenuation in transmission media.	Latency: total time required for a packet to travel from source to destination. Jitter: variation or fluctuation in packet arrival latency (highly disruptive to real-time voice and video). Packet Loss: percentage of sent packets that fail to reach the destination due to congestion or corruption. Attenuation: gradual loss of electrical or optical signal strength over transmission distance.
14	Explain the step-by-step DNS resolution process for a client querying a new external domain name.	1. Client checks local DNS cache and hosts file; 2. Client queries local recursive DNS resolver; 3. If cache miss, recursive resolver queries Root Nameserver ('.'); 4. Root server refers resolver to Top-Level Domain (TLD) nameserver (e.g., '.com'); 5. TLD server refers resolver to authoritative nameserver for domain; 6. Authoritative server returns IP address; 7. Resolver caches answer and returns it to client.
15	What port numbers and transport protocols are used by HTTP, HTTPS, DNS, DHCP, SMTP, POP3, and IMAP?	HTTP: TCP 80; HTTPS: TCP 443; DNS: UDP/TCP 53; DHCP: UDP 67 (server) & UDP 68 (client); SMTP: TCP 25 (relay) / 587 (submission); POP3: TCP 110 (unencrypted) / 995 (POP3S); IMAP: TCP 143 (unencrypted) / 993 (IMAPS).
16	How does Address Resolution Protocol (ARP) operate, and what is ARP Spoofing / Poisoning?	ARP resolves a known Layer 3 IPv4 address to an unknown Layer 2 MAC address. A host broadcasts an ARP Request ('Who has 192.168.1.1? Tell MAC A'); target responds with a unicast ARP Reply. ARP Spoofing occurs when an attacker broadcasts fraudulent ARP replies linking the attacker's MAC address to the default gateway's IP, intercepting subnet traffic (MitM attack).
17	Explain the difference between Static NAT, Dynamic NAT, and Port Address Translation (PAT / NAT Overload).	Static NAT: one-to-one permanent mapping of an internal private IP to an external public IP (used for inbound hosting of web/mail servers). Dynamic NAT: many-to-many temporary mapping from a registered pool of public IPs. PAT (NAT Overload): maps multiple private internal IPs to a single public IP address by assigning unique Layer 4 source port numbers.
18	What are the primary hardware devices and protocols associated with OSI Layer 1 (Physical) versus Layer 2 (Data Link)?	Layer 1 (Physical): Hubs, repeaters, network cables (Cat6, fiber optic), wireless transceivers; handles electrical voltages, bits, and radio frequencies. Layer 2 (Data Link): Network Interface Cards (NICs), Layer 2 switches, bridges; uses 48-bit MAC addresses (EUI-48), Ethernet (802.3), Wi-Fi frames (802.11), and Frame Check Sequence (FCS/CRC).
19	What is the function of IEEE 802.1Q in Virtual Local Area Networks (VLANs), and what is a Native VLAN?	802.1Q is the industry standard for VLAN trunking. It inserts a 4-byte tag into the Ethernet frame header containing a 12-bit VLAN ID (VID, allowing 4,096 VLANs). The Native VLAN is the single VLAN designated on an 802.1Q trunk port whose frames are transmitted across the trunk untagged (default VLAN 1).
20	What are the mathematical formulas for calculating the number of subnets and usable host IP addresses per subnet in IPv4?	Number of subnets = 2^s, where s is the number of borrowed subnet bits. Number of usable hosts per subnet = 2^h - 2, where h is the number of remaining host bits (subtracting 2 for the Network Address and the Broadcast Address). For example, /26 has 6 host bits: 2^6 - 2 = 62 usable hosts.
21	Compare the IEEE Wi-Fi standards: 802.11b, 802.11a, 802.11g, 802.11n (Wi-Fi 4), 802.11ac (Wi-Fi 5), and 802.11ax (Wi-Fi 6).	802.11b: 2.4 GHz, up to 11 Mbps; 802.11a: 5 GHz, up to 54 Mbps; 802.11g: 2.4 GHz, up to 54 Mbps; 802.11n (Wi-Fi 4): 2.4 and 5 GHz, up to 600 Mbps (introduced MIMO); 802.11ac (Wi-Fi 5): 5 GHz only, up to 6.9 Gbps (introduced MU-MIMO); 802.11ax (Wi-Fi 6/6E): 2.4, 5, and 6 GHz, up to 9.6 Gbps (introduced OFDMA and BSS coloring).
22	Compare Star, Mesh, and Bus network topologies regarding fault tolerance and single points of failure.	Star: all nodes connect to a central switch/hub; failure of a cable affects only one host, but central switch failure collapses the network. Full Mesh: every node connects to every other node (n*(n-1)/2 links); maximum fault tolerance and redundancy, but highest cabling and port costs. Bus: all nodes share a single trunk cable; breaks in cable disrupt the entire bus.
23	What are the structural rules for compressing an IPv6 address, and what does 2001:0db8:0000:0000:0000:0000:1428:57ab compress to?	Rules: 1. Omit leading zeros in any 16-bit hextet (e.g., 0db8 becomes db8); 2. Replace one contiguous sequence of all-zero hextets with a double colon '::' (can only be done once per address to avoid ambiguity). The address compresses to: 2001:db8::1428:57ab.
24	What port numbers and transport protocols are used by SNMP, LDAP, LDAPS, NTP, SMB, and Syslog?	SNMP: UDP 161 (queries) & UDP 162 (traps); LDAP: TCP/UDP 389; LDAPS: TCP 636; NTP: UDP 123 (Network Time Protocol); SMB: TCP 445; Syslog: UDP 514 (default) or TCP 6514 (Syslog over TLS).
25	What is Link Aggregation (IEEE 802.3ad / 802.1AX LACP), and what are its benefits?	Link Aggregation combines multiple physical Ethernet links between two switches into a single logical high-bandwidth channel (EtherChannel/Port Channel). Benefits: multiplies aggregate bandwidth, provides automated load balancing across links, and provides transparent link failover without triggering Spanning Tree recalculation.
26	Compare Router-on-a-Stick and Layer 3 Switch implementations for Inter-VLAN Routing.	Router-on-a-Stick: uses a single physical router interface connected to a switch trunk port, divided into logical subinterfaces for each VLAN (limited by router interface bandwidth). Layer 3 Switch: routes traffic between VLANs internally using Switch Virtual Interfaces (SVIs) and dedicated ASIC hardware, providing line-rate wire-speed routing with significantly lower latency.
27	Compare OSI Layer 3 (Network) and Layer 4 (Transport) responsibilities and protocols.	Layer 3 (Network): Path determination, logical addressing, and packet forwarding across network boundaries (IPv4, IPv6, ICMP, IPsec, routers). Layer 4 (Transport): End-to-end host communication, port-level multiplexing, segmentation, and reliability. TCP provides connection-oriented, reliable, sequenced delivery with flow control; UDP provides connectionless, best-effort datagram delivery.
28	Compare SNMPv1/v2c with SNMPv3 regarding security and cryptographic capabilities.	SNMPv1 and SNMPv2c transmit community strings (passwords) in cleartext across the network, allowing eavesdropping and unauthorized configuration changes. SNMPv3 introduces User-based Security Model (USM) providing: Authentication (HMAC-MD5/SHA), Encryption/Privacy (AES/DES for payload confidentiality), and Message Integrity.
29	Why is Spanning Tree Protocol (STP 802.1D) essential in switched Ethernet networks, and what hazards does it prevent?	STP prevents Layer 2 switching loops in topologies with redundant physical switch uplinks. Without STP, Layer 2 broadcast frames circulate infinitely, causing Broadcast Storms, MAC database instability (MAC address flapping), and multiple duplicate frame copies delivered to end stations, crashing switch CPUs.
30	What are the three RFC 1918 Private IPv4 address ranges and the APIPA address block?	Class A Private: 10.0.0.0/8 (10.0.0.0 to 10.255.255.255); Class B Private: 172.16.0.0/12 (172.16.0.0 to 172.31.255.255); Class C Private: 192.168.0.0/16 (192.168.0.0 to 192.168.255.255). APIPA (Automatic Private IP Addressing): 169.254.0.0/16 (used when DHCP client cannot reach a DHCP server).
31	Compare WPA2 and WPA3 wireless security protocols, highlighting Simultaneous Authentication of Equals (SAE).	WPA2 uses AES-CCMP encryption and Pre-Shared Key (PSK), which is vulnerable to offline dictionary/brute-force attacks if an attacker captures the 4-way handshake. WPA3 replaces PSK with Simultaneous Authentication of Equals (SAE / Dragonfly handshake), providing forward secrecy and rendering offline dictionary attacks impossible even with weak passwords.
32	List the 7 layers of the OSI Model from Layer 7 to Layer 1 and their corresponding Protocol Data Units (PDUs).	Layer 7: Application (Data); Layer 6: Presentation (Data); Layer 5: Session (Data); Layer 4: Transport (Segments for TCP / Datagrams for UDP); Layer 3: Network (Packets); Layer 2: Data Link (Frames); Layer 1: Physical (Bits). Remember: All People Seem To Need Data Processing.