CompTIA Network+ (N10-008) - Networking Infrastructure & Subnetting Flashcards

Question 1

How do you calculate the number of usable host IP addresses in an IPv4 subnet?

Accepted Answer

Use the formula $2^h - 2$, where $h$ is the number of host bits (calculated as $32 - 	ext{CIDR prefix}$). The subtraction of 2 accounts for the unusable network address (all host bits 0) and the broadcast address (all host bits 1).

Question 2

How do you calculate the number of subnets created when borrowing host bits?

Accepted Answer

Use the formula $2^n$, where $n$ is the number of host bits borrowed from the host portion to create the subnet prefix.

Question 3

What is the subnet mask and number of usable hosts for a `/28` CIDR prefix?

Accepted Answer

The subnet mask is `255.255.255.240`. With $h = 32 - 28 = 4$ host bits, there are $2^4 - 2 = 14$ usable host IP addresses per subnet.

Question 4

What are the three private IPv4 address ranges defined by RFC 1918?

Accepted Answer

1. **Class A:** `10.0.0.0` to `10.255.255.255` (`10.0.0.0/8`)
2. **Class B:** `172.16.0.0` to `172.31.255.255` (`172.16.0.0/12`)
3. **Class C:** `192.168.0.0` to `192.168.255.255` (`192.168.0.0/16`)

Question 5

What is the structure of an IPv6 address, and what is its loopback address?

Accepted Answer

An IPv6 address is 128 bits long, represented as eight 16-bit blocks in hexadecimal separated by colons. Its loopback address is `::1` (equivalent to IPv4 `127.0.0.1`).

Question 6

What are the two primary rules for compressing IPv6 addresses?

Accepted Answer

1. **Omit leading zeros** in any individual 16-bit field (e.g., `0001` becomes `1`).
2. **Double colon (`::`)** replaces contiguous blocks of all-zero fields (can only be used once per address).

Question 7

Compare OSPF and BGP routing protocols.

Accepted Answer

- **OSPF (Open Shortest Path First):** An Interior Gateway Protocol (IGP) using a link-state routing algorithm within a single Autonomous System (AS).
- **BGP (Border Gateway Protocol):** An Exterior Gateway Protocol (EGP) using a path-vector routing algorithm to route traffic between different ASes across the Internet.

Question 8

What is Administrative Distance (AD), and what are the default AD values for Directly Connected, Static, eBGP, and OSPF?

Accepted Answer

AD rates the trustworthiness of routing sources (lower value = higher preference).
- **Directly Connected:** `0`
- **Static Route:** `1`
- **eBGP:** `20`
- **OSPF:** `110`

Question 9

Identify the standard protocol and transport type for ports `22`, `53`, `80`, and `443`.

Accepted Answer

- **Port 22:** SSH / SFTP (TCP)
- **Port 53:** DNS (UDP for queries, TCP for zone transfers)
- **Port 80:** HTTP (TCP)
- **Port 443:** HTTPS (TCP)

Question 10

Identify the standard protocol for ports `67/68`, `123`, `161/162`, and `3389`.

Accepted Answer

- **Ports 67/68:** DHCP (UDP)
- **Port 123:** NTP (UDP)
- **Ports 161/162:** SNMP / SNMP Trap (UDP)
- **Port 3389:** RDP (TCP/UDP)

Question 11

Compare Star and Full Mesh network topologies.

Accepted Answer

- **Star:** Central device (switch) connects to all nodes. Easy to scale; single point of failure at the switch.
- **Full Mesh:** Every node connects to every other node. Extremely redundant. Required links formula: $N(N - 1) / 2$, where $N$ is the number of nodes.

Question 12

What is a Spine-Leaf architecture and why is it used in data centers?

Accepted Answer

A two-tier data center topology where every leaf switch (connecting to servers) connects to every spine switch. It guarantees predictable, equal-distance, low-latency east-west traffic flow and prevents bandwidth bottlenecks.

Question 13

What is the color sequence for T568B wiring, and how does a crossover cable differ?

Accepted Answer

**T568B Order:** Pin 1: White/Orange, Pin 2: Orange, Pin 3: White/Green, Pin 4: Blue, Pin 5: White/Blue, Pin 6: Green, Pin 7: White/Brown, Pin 8: Brown.
A **crossover cable** has T568A on one end and T568B on the other, swapping transmit (pins 1&2) and receive (pins 3&6) pairs.

Question 14

Compare Single-Mode Fiber (SMF) and Multi-Mode Fiber (MMF).

Accepted Answer

- **Single-Mode Fiber (SMF):** Small core diameter (~9 µm), uses laser light, supports high bandwidth over long distances (up to tens of kilometers).
- **Multi-Mode Fiber (MMF):** Larger core diameter (50/62.5 µm), uses LED or VCSEL light, limited to short distances (e.g., < 550m) due to modal dispersion.

Question 15

Compare Coarse Wavelength Division Multiplexing (CWDM) and Dense Wavelength Division Multiplexing (DWDM).

Accepted Answer

- **CWDM:** Uses wider channel spacing (20 nm), supporting up to 18 channels; cheaper, suited for shorter ranges.
- **DWDM:** Uses tight channel spacing (0.8 nm or less), supporting hundreds of channels over long distances via optical amplifiers.

Question 16

What is IEEE 802.1Q and how does it modify an Ethernet frame?

Accepted Answer

802.1Q is the networking standard for VLAN trunking. It inserts a 4-byte VLAN tag into the Ethernet frame header between the Source MAC Address and the EtherType fields.

Question 17

Compare ARP in IPv4 to NDP in IPv6.

Accepted Answer

- **ARP (Address Resolution Protocol):** Maps IPv4 addresses to MAC addresses using broadcast requests.
- **NDP (Neighbor Discovery Protocol):** Replaces ARP in IPv6, using ICMPv6 multicast messages (`Neighbor Solicitation` and `Neighbor Advertisement`) to resolve Layer 2 addresses.

Question 18

What is Maximum Transmission Unit (MTU) and how does Path MTU Discovery (PMTUD) work?

Accepted Answer

MTU is the maximum Layer 3 packet size (default Ethernet MTU is 1500 bytes). PMTUD sets the 'Don't Fragment' (DF) flag on packets and uses ICMP 'Destination Unreachable - Fragmentation Needed' messages to find the lowest MTU along a network path.

Question 19

Compare MPLS and SD-WAN technologies.

Accepted Answer

- **MPLS:** Protocol-agnostic WAN mechanism that routes traffic using short path labels; offers guaranteed QoS/SLAs but is expensive and slow to provision.
- **SD-WAN:** Software-defined overlay that dynamically routes traffic across multiple transport links (broadband, LTE, MPLS) based on real-time performance policy.

Question 20

How do you troubleshoot Layer 1 vs. Layer 3 network issues?

Accepted Answer

- **Layer 1 (Physical):** Check link lights, replace patch cables, run cable diagnostics using TDR/OTDR, and check `show interface` for speed/duplex mismatches or CRC errors.
- **Layer 3 (Network):** Verify IP configuration, check default gateways and routing tables using `ipconfig`/`ifconfig`, `ping`, `traceroute`/`tracert`, and `route print`.

CompTIA Network+ (N10-008) - Networking Infrastructure & Subnetting

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