🧪 Session 2 — Connecting PCs, Switches & Understanding Ping

🗓️ Overview

In this session, we learned how to connect multiple computers using Cisco Packet Tracer and explore how devices communicate through IP addressing and the ping command. We were also introduced to switches, routers, hubs, and the command-line modes used to configure network devices.

🔌 Part 1 — Building a Simple Network in Cisco Packet Tracer

🧱 Components Used

Device	Function
PCs (End Devices)	Represent individual computers on a network
Switch	Connects multiple PCs in the same local network (LAN)
Cables (Copper Straight-Through)	Used to connect PCs to the switch

💡 Tip: Use “Copper Straight-Through” cables when connecting different device types (e.g., PC ↔ Switch). Use “Crossover” cables only between similar device types (e.g., PC ↔ PC).

⚙️ Steps Performed

Open Cisco Packet Tracer.
Add 3 PCs from the End Devices panel.
Add 1 Switch (e.g., 2960 series switch) from the Switches panel.
Connect each PC to the switch using Copper Straight-Through cables.
Click each PC → Desktop tab → IP Configuration.
Assign IP addresses and Subnet Masks manually, e.g.:

Device	IP Address	Subnet Mask
PC1	192.168.1.1	255.255.255.0
PC2	192.168.1.2	255.255.255.0
PC3	192.168.1.3	255.255.255.0

Open Command Prompt on one PC → type:
```
ping 192.168.1.2
```
If the setup is correct, you’ll receive reply messages from the target computer.

📡 Part 2 — Understanding How `ping` Works

🔍 What Is Ping?

ping is a network utility used to test whether one device can reach another over a network.

When you type ping <IP address>:

Your computer sends an ICMP Echo Request message.
The target computer (if reachable) replies with an ICMP Echo Reply.
The round-trip time is measured and displayed.

📚 ICMP stands for Internet Control Message Protocol — it operates at the Network Layer (Layer 3) of the OSI model.

⚙️ Ping Message Types

Message Type	Description
Echo Request	Sent by the source computer to test connectivity
Echo Reply	Sent by the target computer as a response
Destination Unreachable	Indicates the target can’t be reached
Time Exceeded (TTL Expired)	Packet’s lifetime expired before reaching the destination

⏱️ What Is TTL (Time to Live)?

Each packet sent in a network has a TTL value, usually starting at 64, 128, or 255.
Every time the packet passes through a router, the TTL decreases by 1.
If TTL reaches 0, the packet is discarded (dropped).
This prevents packets from looping endlessly in the network.

💡 Think of TTL as a packet’s expiration date.

🔄 Part 3 — Hub vs Switch vs Router

Device	OSI Layer	Function	Key Points
Hub	Layer 1 (Physical)	Sends data to all connected devices (no intelligence)	Old & rarely used; causes collisions
Switch	Layer 2 (Data Link)	Sends data only to the target device (uses MAC address)	Forms the basis of LANs
Router	Layer 3 (Network)	Connects different networks together using IP addresses	Directs traffic between networks

⚡ Summary:

Use Switches to connect devices within the same network.

Use Routers to connect different networks (e.g., LAN ↔ Internet).

🧮 Part 4 — Device Command Modes (Switch/Router CLI)

Cisco devices have different modes that determine your level of control.

Mode	Prompt Example	Access Level	Description
User EXEC Mode	`Switch>`	Limited	Basic monitoring (no configuration allowed)
Privileged EXEC Mode	`Switch#`	Intermediate	View device details, enter configuration mode
Global Configuration Mode	`Switch(config)#`	Full	Configure the device (interfaces, VLANs, etc.)

⚙️ Moving Between Modes

Switch> enable                # Enter privileged mode
Switch# configure terminal     # Enter global configuration mode
Switch(config)# exit           # Return to privileged mode
Switch# disable                # Return to user mode

💡 Tip:

User mode = view only

Privileged mode = view & diagnose

Global config = make actual changes

🧠 Exam Notes & Common Mistakes

Don’t confuse Hub and Switch — only the switch learns MAC addresses.
Ping doesn’t use TCP or UDP; it uses ICMP.
TTL doesn’t measure time in seconds — it counts network hops.
You cannot ping across different networks without a router.
Make sure all devices are in the same subnet (same first 3 octets in IPv4) when testing connectivity in a LAN.

🏁 Summary

In this lab, we:

Connected multiple PCs using a switch.
Assigned static IP addresses.
Verified connectivity using the ping command.
Understood ICMP, TTL, and device types (hub/switch/router).
Learned about Cisco command modes for configuration.