Top 50 - Part 1

1. Which physical network topology connects all endpoints directly to a single central hardware device, ensuring that an individual cable break only affects a solitary node but creating a single point of failure?

Star Topology.

                 [Node A]
                    │
                    │
[Node B] ─────── [Switch] ─────── [Node C]
                    │
                    │
                 [Node D]

        ↑
   Central device
   (single point of failure)

All devices connect to one central hub or switch.

• Good: one cable break only kills that one node.
• Bad: the central device is a single point of failure — if the hub dies, the whole network dies.

Cable B breaks:

[Node B]     X──────[Switch]──────[Node C]
                      │
                   [Node A]
                      │
                   [Node D]

Only Node B is disconnected.
The rest of the network still works.

• Mesh — every node connects to many others (maximum redundancy).
• Bus — all nodes share one backbone cable.
• Ring — each node connects to exactly two neighbors in a loop.

Star is the standard for modern LANs because the central switch is cheap and failures are easy to isolate.

---

2. How is a Hybrid Topology defined in enterprise network design?

A hybrid topology combines two or more distinct base topologies into one network.

             Star Network
          ┌─────┼─────┐
          │     │     │
        [PC]   [PC]  [PC]
          │     │     │
         [H1]  [H1]  [H1]
           \     │     /
            \    │    /
             \   │   /
          ===== BUS BACKBONE =====
                    │
               [H2] [H2] [H2]
                │    │    │
               [PC] [PC] [PC]
                  Star Network

Common examples:

• Star-Bus — star workgroups hanging off a shared bus backbone.
• Star-Ring — star workgroups connected in a ring at the core.

Why use one? Different parts of an organization have different needs. A department might want a star for fault tolerance, while the backbone between buildings is a ring or bus. Hybrid gives you the strengths of each where they matter — at the cost of complexity.

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3. What is the operational difference between Baseband and Broadband network transmissions?

• Baseband — uses the entire bandwidth of the medium to carry one digital signal at a time. Standard Ethernet is baseband (that’s the “Base” in 100Base-T).
• Broadband — splits the medium into multiple frequency channels, each carrying a separate analog signal concurrently. That’s how cable TV and DOCSIS internet share one coax line.

BASEBAND
────────────────────────────────────────
        ONE signal uses the medium
────────────────────────────────────────
        [ DIGITAL DATA ]
             ───────→


BROADBAND
────────────────────────────────────────
| Channel 1 | Channel 2 | Channel 3 | Channel 4 |
|   TV      |   TV      | Internet  |   Phone   |
────────────────────────────────────────
        Multiple signals at once

Think of baseband as a single-lane road and broadband as a multi-lane highway where each lane is a different channel.

---

4. What is Signal Attenuation, and how is it practically corrected over long cable distances?

Attenuation is the progressive loss of signal strength as it travels down a medium, caused by the medium’s resistance.

Signal strength

Strong
  │
  │ ██████████
  │ ████████
  │ ██████
  │ ████
  │ ██
  │ █
  └──────────────────────────────→ Distance
     Source              Destination

     Strong signal  ─────────→  Weak signal

The longer the cable, the weaker the signal — until it’s too weak to decode reliably.

The fix: a repeater (or hub) receives the degraded signal, regenerates/amplifies it back to full strength, and resends it.

[Source]
   │
   │ Strong signal
   ▼
─────────────── cable ───────────────
                         ↓
                    Weak signal
                         │
                         ▼
                    [Repeater]
                         │
                    Regenerated
                    strong signal
                         │
                         ▼
                    [Destination]

• Attenuation = strength loss over distance.
• Repeaters/hubs = regenerate the signal.

---

5. Which of the following describes the phenomenon of Crosstalk in copper network cabling?

Crosstalk is electromagnetic interference where the signal from one wire pair bleeds into an adjacent pair inside the same cable.

Normal:

Pair 1  ─────────────────────────→
Pair 2  ─────────────────────────→


Crosstalk:

Pair 1  ──────── SIGNAL ─────────→
                    ↓
                    ↓ leakage
                    ↓
Pair 2  ──────── noise ──────────→

Why it happens: every wire carrying current radiates a small electromagnetic field. In a multi-pair cable, that field couples into neighboring pairs, distorting their signals and causing bit errors.

The fixes:

• Twisting the pairs together (twisted pair) cancels most of the bleed — hence the name.
• Shielding (STP, foil) blocks external interference.

Twisted Pair:

Wire A:  /\/\/\/\/\/\/\/\/\
Wire B:  \/\/\/\/\/\/\/\/\/

      ↑
   Twisting helps
   reduce interference

That’s exactly why UTP cabling is twisted: each wire’s twist keeps its own field contained.

---

6. What do the physical specifications of a 100Base-FX network standard indicate?

Decompose the name:

100Base-FX
│   │    │
│   │    └── FX = Fiber optic
│   └─────── Base = Baseband
└─────────── 100 = 100 Mbps

So 100Base-FX = 100 Mbps over baseband fiber-optic cabling.

The IEEE naming convention is consistent:

100Base-T
│   │   │
│   │   └── Twisted pair
│   └────── Baseband
└────────── 100 Mbps

• 100Base-T — 100 Mbps, baseband, twisted pair (copper)
• 10Base-T — 10 Mbps, baseband, twisted pair
• 10Base-2 / 10Base-5 — 10 Mbps, baseband, coaxial (Thinnet/Thicknet)

Speed first, then signaling type, then media.

---

7. How did legacy Thinnet (10Base2) and Thicknet (10Base5) coaxial cables compare in maximum run length?

	Thinnet (10Base2)	Thicknet (10Base5)
Diameter	Thin, flexible	Thick, stiff
Max length	185 m	500 m
Typical use	Workstation segments	Network backbone

THINNET (10Base2)

[PC]──────────────[PC]──────────────[PC]
       ←──── max 185 m ────→


THICKNET (10Base5)

[PC]──────────────────────────────────────────[PC]
             ←──── max 500 m ────→

• Thinnet — thinner coaxial, cheaper and easier to route, but only reaches 185 meters.
• Thicknet — thicker, more expensive, harder to bend, but reaches 500 meters, so it served as backbones.

Reach comparison:

Thinnet   : ███████████████ 185 m
Thicknet  : ████████████████████████████████████████ 500 m

Same 10 Mbps speed in both; the trade-off was flexibility vs. reach.

---

8. What is the structural and functional difference between an RJ11 connector and an RJ45 connector?

	RJ11	RJ45
Size	Smaller	Wider
Pins	4–6	8
Pairs supported	1–2	4
Use	Analog telephone lines	Ethernet (twisted-pair)

RJ11 — Telephone

┌──────────────┐
│ •  •  •  •   │
└──────────────┘
   4–6 pins


RJ45 — Ethernet

┌──────────────────────┐
│ • • • • • • • •      │
└──────────────────────┘
      8 pins

Size:

RJ11                 RJ45
┌──────────┐         ┌────────────────┐
│ • • • •  │         │ • • • • • • • •│
└──────────┘         └────────────────┘
   Smaller                Wider

RJ11 is the classic telephone jack — small, 4–6 pins. RJ45 is the bigger Ethernet plug, housing 8 pins for the 4 twisted pairs inside a standard Cat5e/6 cable. They look similar at a glance, but they don’t fit each other’s jacks.

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9. What is a Multi-Homed Host in network infrastructure architecture?

A multi-homed host is a device with two or more active network interfaces connected to separate networks at the same time.

                  Multi-Homed Server

       Internet                 Internal LAN
           │                         │
           │                         │
        ┌──┴──┐                   ┌──┴──┐
        │ NIC0│                   │ NIC1│
        └──┬──┘                   └──┬──┘
           │                         │
           └────────[ SERVER ]───────┘

Why run multi-homed?

             ┌───────────────┐
Internet ───→│    Server     │
             │               │
LAN ────────→│ NIC0     NIC1 │
             └───────────────┘
                ↑         ↑
             Network 1  Network 2

• Redundancy — if one link fails, traffic moves to the other.
• Load balancing — spread traffic across links.
• Routing — a box that bridges two separate networks.

A classic example is a firewall or proxy with one NIC on the internet-facing network and another on the trusted internal network.

---

10. What is the function of a Pseudo TTY (Teletypewriter) in modern server operating systems?

A pseudo TTY (PTY) is a software-emulated virtual terminal that behaves like a real physical terminal (TTY).

        Your Computer
             │
             │ SSH
             ▼
       [ SSH Server ]
             │
             ▼
       [ Pseudo TTY ]
          (virtual
           terminal)
             │
             ▼
          [ Shell ]
          /bin/bash
             │
             ▼
       $ ls
       $ cd
       $ top

Why it’s needed: programs like SSH and Telnet need to talk to a shell (like bash), and the shell expects a terminal device. A PTY fakes that — it presents the shell with a terminal interface while the actual bytes travel over a network connection.

SSH Client
    │
    │ keyboard input
    ▼
[ PTY ] ─────→ [ Shell ]
                  │
                  │ output
                  ▼
                [ PTY ]
                  │
                  │ network
                  ▼
             SSH Client

Without PTYs, you couldn’t run interactive programs over SSH. It’s the plumbing that makes remote command-line access work.

---

11. What is the structural operational difference between a MAC Flooding attack and an ARP Poisoning attack?

• MAC Flooding — attacks a switch’s CAM (MAC address) table. The attacker floods fake MAC entries until the table overflows. The switch can’t learn real mappings, so it fails open and broadcasts everything like a hub — letting the attacker sniff traffic between other hosts.
• ARP Poisoning — attacks hosts’ ARP caches. The attacker sends forged ARP replies associating their MAC address with a legitimate IP. Traffic meant for that IP gets redirected to the attacker (a classic MitM setup).

MAC FLOODING

Attacker
   │
   │ Thousands of fake MAC addresses
   ▼
┌───────────────┐
│    SWITCH     │
│   CAM TABLE   │
│               │
│ MAC → Port    │
│ MAC → Port    │
│ MAC → Port    │
│ MAC → Port    │
│ ... OVERFLOW  │
└───────────────┘
        │
        ▼
 Switch may flood frames
 like a hub

ARP POISONING

Normal:

PC A ───────────────→ PC B
       direct traffic


Poisoned:

PC A ─────→ Attacker ─────→ PC B
             ↑
       fake ARP mapping
       "PC B's IP = my MAC"

MAC Flooding:
Fake MACs → CAM table overflow → switch floods traffic

ARP Poisoning:
Fake IP↔MAC mapping → victim sends traffic → attacker intercepts

One breaks the switch’s forwarding memory; the other poisons the address-resolution cache.

---

12. How does a Multi-Layer Switch (MLS) differ from a traditional standard Layer 2 Switch?

• Layer 2 switch — forwards frames within a segment using MAC addresses. It can’t route between subnets.
• Multi-Layer Switch (MLS) — does Layer 2 switching and has built-in hardware routing engines to forward packets between subnets using IP addresses.

Layer 2 Switch

PC A ──→ [ L2 SWITCH ] ──→ PC B
           │
        MAC-based
        forwarding
           │
        Same subnet

Multi-Layer Switch

Subnet A                  Subnet B
192.168.1.0/24            192.168.2.0/24
     │                          │
 [PC A]                      [PC B]
     │                          │
     └────→ [ MLS ] ←──────────┘
              │
        MAC + IP routing
              │
       Layer 2 + Layer 3

Layer 2 Switch:
[ MAC forwarding only ]
          ↓
     One subnet


Multi-Layer Switch:
[ MAC forwarding ]
        +
[ IP routing ]
        ↓
    Multiple subnets

An MLS is essentially a switch + router in one box, with routing done in hardware (ASICs) so it’s much faster than a general-purpose router. Used heavily in data centers and campus networks where you need both functions at line rate.

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13. How do the metric calculations of the Open Shortest Path First (OSPF) protocol differ from the Border Gateway Protocol (BGP)?

• OSPF (interior gateway protocol, runs inside one AS) computes a Cost = reference bandwidth / link bandwidth. Faster links → lower cost → preferred path. Pure technical optimization.
• BGP (exterior gateway protocol, runs between ASes) uses Path Vector attributes — AS-path length, next-hop, local preference, MED — and applies administrative policy rules.

OSPF

        cost 10
     ┌────────────┐
     │            ▼
   [A] ──────── [B]
    │
    │ cost 1
    ▼
   [C] ──────── [B]
        cost 5

Path A → B:
10

Path A → C → B:
1 + 5 = 6   ← OSPF prefers this

BGP

             ISP-A
            Path 1
              │
              ▼
          [ Network ]
              ▲
              │
            Path 2
              │
             ISP-B

BGP asks:

"Which path does policy prefer?"
        │
        ├── Local Preference
        ├── AS Path
        ├── MED
        └── Other attributes

OSPF picks the fastest/lowest-cost path; BGP picks the path the policies say to use.

OSPF → technical metric
       "Which path has the lowest cost?"

BGP  → administrative policy
       "Which path do we WANT to use?"

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14. Which variant of the Carrier Sense Multiple Access (CSMA) protocol is deployed in wireless networks, and how does it function?

Wireless uses CSMA/CA — Collision Avoidance.

Why not CSMA/CD? Wired Ethernet can detect collisions (listen while transmitting — voltage conflicts are obvious). Radios can’t easily do that: the transmitter is drowning out the receiver, and you can’t reliably “hear” a collision mid-transmission. So wireless avoids collisions instead of detecting them.

CSMA/CA process:

1. LISTEN
   │
   ▼
Is channel free?
   │
   ├── NO ──→ Wait / backoff
   │
   └── YES
        │
        ▼
2. RESERVE
   │
   ├── RTS → AP
   │
   └── CTS ← AP
        │
        ▼
3. TRANSMIT
   │
   └── Data → AP
        │
        ▼
4. ACK
   │
   ├── ACK received → Success
   │
   └── No ACK → Retry

Client                    Access Point
  │                            │
  │──── RTS ──────────────────→│
  │                            │
  │←─── CTS ───────────────────│
  │                            │
  │──── DATA ──────────────────→│
  │                            │
  │←─── ACK ───────────────────│

Proactive handshaking keeps wireless collisions rare — at the cost of extra control overhead.

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15. What characterizes a Private IP address space as defined by RFC 1918 rules?

Private IPs are reserved for internal local networks and cannot be routed on the public internet without NAT.

The RFC 1918 ranges:

┌────────────────────────────────────────────────────────────┐
│                PRIVATE IPv4 ADDRESS SPACE                  │
├──────────────────┬─────────────────────────────────────────┤
│ 10.0.0.0/8       │ 10.0.0.0   – 10.255.255.255           │
│ 172.16.0.0/12    │ 172.16.0.0  – 172.31.255.255          │
│ 192.168.0.0/16   │ 192.168.0.0 – 192.168.255.255         │
└──────────────────┴─────────────────────────────────────────┘

             PRIVATE NETWORK
                   │
          ┌────────┴────────┐
          │                 │
      [PC 1]             [PC 2]
   192.168.1.10       192.168.1.20
          │                 │
          └────────┬────────┘
                   │
                [Router]
                   │
                  NAT
                   │
                   ▼
             PUBLIC INTERNET
             Public IP:
             203.x.x.x

Key facts:

• Internet routers drop these addresses — they only work inside a private network.
• Many devices inside a LAN can reuse the same private range (e.g., every home router hands out 192.168.x.x).
• To reach the internet, a device uses NAT at the edge — the router translates the private IP into its single public IP.

Private IP                    Public IP
192.168.1.10 ──→ [ NAT Router ] ──→ 203.x.x.x
192.168.1.20 ──→ [ NAT Router ] ──→ 203.x.x.x
192.168.1.30 ──→ [ NAT Router ] ──→ 203.x.x.x

          Many private devices
                  │
                  ▼
          One public address

Private space solves IPv4 exhaustion by letting billions of devices share far fewer public addresses.