🌐 Static Routing — Practical + Interview Guide

📌 What is Static Routing?

Static routing is a method where routes are manually configured on routers to define how packets should reach different networks.

👉 Simple:

“Router ko manually batate hain traffic kahan bhejna hai.”

🎯 What You Will Learn

• Communication between different networks
• How routers forward packets
• Real-world routing logic

🧪 Lab Setup (in Cisco Packet Tracer)

🔹 Topology

PC1 --- Router1--- Router2 --- PC2

Lab Topology & IP Addressing Plan

Step 1 — Build topology in Packet Tracer

• Drag 2 x Router 2911 and 2 x PC
• Connect PC1 → Router1 with Copper Straight-Through
• Connect Router1 → Router2 with Copper Cross-Over (or Serial DCE)
• Connect Router2 → PC2 with Copper Straight-Through

Step 2 — Configure IP addresses

Router 1:

Router> enable
Router# configure terminal
Router(config)# hostname R1
R1(config)# interface GigabitEthernet 0/0
R1(config-if)# ip address 192.168.1.1 255.255.255.0
R1(config-if)# no shutdown
R1(config-if)# exit
R1(config)# interface GigabitEthernet 0/1
R1(config-if)# ip address 10.0.0.1 255.255.255.252
R1(config-if)# no shutdown
R1(config-if)# end

Router 2:

Router> enable
Router# configure terminal
Router(config)# hostname R2
R2(config)# interface GigabitEthernet 0/0
R2(config-if)# ip address 10.0.0.2 255.255.255.252
R2(config-if)# no shutdown
R2(config-if)# exit
R2(config)# interface GigabitEthernet 0/1
R2(config-if)# ip address 192.168.3.1 255.255.255.0
R2(config-if)# no shutdown
R2(config-if)# end

Step 3 — Add Static Routes ⭐ (Most important!)

ip route [destination network] [subnet mask] [next-hop IP]
On Router 1 — tell it how to reach Network 3:
R1(config)# ip route 192.168.3.0 255.255.255.0 10.0.0.2

On Router 2 — tell it how to reach Network 1:
R2(config)# ip route 192.168.1.0 255.255.255.0 10.0.0.1

Step 4 — Configure PCs

On PC1 → Desktop → IP Configuration:

IP: 192.168.1.10, Mask: 255.255.255.0, Gateway: 192.168.1.1

On PC2 → Desktop → IP Configuration:

IP: 192.168.3.10, Mask: 255.255.255.0, Gateway: 192.168.3.1

Step 5 — Test with Ping

• On PC1 → Desktop → Command Prompt:
• ping 192.168.3.10
• You should see 4 replies ✅

Might be possible first time when you will ping it will only 2 replies came and others packets loss but second time if you try definitely ping successfully and winner winner !!

Verify on Router

R1# show ip route

R1# show running-config

Common mistakes to avoid:

• Forgetting no shutdown on interfaces
• Wrong next-hop IP (must be the directly connected neighbor's IP)
• Missing the return route (both routers need static routes!)
• Wrong subnet mask in the ip route command

Inter-VLAN Routing (Router-on-a-Stick)

📌 What is Inter-VLAN Routing?

Inter-VLAN routing is the process of enabling communication between different VLANs using a Layer 3 device (router or L3 switch).

👉 Simple:

“Different VLANs can talk using a router.”

🧪 Lab Topology (Build in Cisco Packet Tracer)

Devices:

• 1 Switch (2960)
• 1 Router (2911)
• 4 PCs

🔹 VLAN Plan

⚙️ Step 1: Assign IP Addresses

⚙️ Step 2: Create VLANs (Switch)

enable
configure terminal

vlan 10
name HR

vlan 20
name IT

⚙️ Step 3: Assign Access Ports

interface fa0/1
switchport mode access
switchport access vlan 10

interface fa0/2
switchport mode access
switchport access vlan 20

interface fa0/3
switchport mode access
switchport access vlan 10

interface fa0/4
switchport mode access
switchport access vlan 20

⚙️ Step 4: Connect Switch → Router (IMPORTANT)

Use Straight-through cable

Connect:

Switch Fa0/23 → Router G0/0

⚙️ Step 5: Make Switch Port TRUNK

• interface fa0/23
• switchport mode trunk

⚙️ Step 6: Configure Router (CORE STEP 🔥)

enable
configure terminal

interface g0/0
no shutdown

interface g0/0.10
encapsulation dot1Q 10
ip address 192.168.10.254 255.255.255.0

interface g0/0.20
encapsulation dot1Q 20
ip address 192.168.20.254 255.255.255.0

🧪 Step 7: Test Connectivity

Same VLAN

ping 192.168.10.2

✔ Works

🔹 Different VLAN (MAIN TEST)

From PC0:

ping 192.168.20.2

✔ Now it will WORK

Important Note:

Ethernet switches remember MAC addresses (Layer 2) to map devices to physical ports, while routers remember IP addresses (Layer 3) to map devices to logical network addresses. Switches use a temporary CAM table, while routers use DHCP leases to "remember" these assignments.

Key Takeaways:

Switch (MAC): Learns source MAC addresses from incoming frames and associates them with a port. These entries are temporary (typical 300-second aging timer).

Router (IP): Assigns IP addresses via DHCP to specific MAC addresses. These assignments ("leases") can be configured as static/persistent.

Function: Switches enable local network communication (same network), while routers manage traffic between different networks.

🔍 What Happens Internally

• PC0 → sends packet to gateway (router)
• Router receives via VLAN 10 sub-interface
• Router routes to VLAN 20
• Sends back to PC3

👉 “Packet goes:

PC → Switch → Router → Switch → Destination”

👉 “Router performs Layer 3 decision”

⚠️ Common Mistakes

• ❌ Forgetting trunk on switch
• ❌ Missing encapsulation dot1Q
• ❌ Wrong default gateway
• ❌ Router interface shutdown

🧠 Key Concepts

• Router uses sub-interfaces
• Each VLAN = one sub-interface
• Router acts as gateway

🎯 Interview Questions

❓ What is Router-on-a-Stick?

👉 Using one physical router interface with multiple sub-interfaces for VLAN routing

❓ Why trunk is required?

👉 To carry multiple VLANs between switch and router

❓ Why ping was failing earlier?

👉 No Layer 3 routing between VLANs

🧠 Real-World Use

Used in:

• Small office networks
• Labs and training
• Basic enterprise setups

Trunking (VLAN Communication Between Switches)

📌 What is Trunking?

A trunk port is a switch port that carries traffic for multiple VLANs using 802.1Q tagging.

👉 Simple:

“One cable, multiple VLANs”

🎯 What You Will Learn

• VLAN communication across switches
• 802.1Q tagging
• Access vs Trunk port difference

🧪 Lab Setup (Build in Cisco Packet Tracer)

🔹 Topology

• 2 Switches (2960)
• 4 PCs

🔹 VLAN Plan

⚙️ Step 1: Assign IP Addresses

⚙️ Step 2: Create VLANs on BOTH Switches

Do this on Switch0 and Switch1

enable
configure terminal

vlan 10
name HR

vlan 20
name IT

exit

switch 0

switch 1

⚙️ Step 3: Assign Access Ports

🔹 Switch0

interface fa0/1
switchport mode access
switchport access vlan 10

interface fa0/2
switchport mode access
switchport access vlan 20

🔹 Switch1

interface fa0/1
switchport mode access
switchport access vlan 10

interface fa0/2
switchport mode access
switchport access vlan 20

⚙️ Step 4: Configure Trunk Port (MOST IMPORTANT)

Assume connection between switches is:

• Switch0 → Fa0/24
• Switch1 → Fa0/24

🔹 On BOTH switches:

interface fa0/24
switchport mode trunk

🧪 Step 5: Test Connectivity

✅ Same VLAN Across Switches (Should Work)

From PC0:

ping 192.168.10.2

✔ Success

❌ Different VLAN (Should Fail)

From PC0:

ping 192.168.20.2

❌ Failed (no routing yet)

If still facing issue 

✅ Step-by-Step Fix

🔌 1. Check Physical Connection (MOST IMPORTANT)

Make sure:

👉 You connected:

Switch0 Fa0/24 → Switch1 Fa0/24

✔ Use Copper Straight-Through

👉 If unsure:

• Delete cable
• Reconnect properly

🔄 2. Check Both Sides

Both ends must be connected:

• Switch0 Fa0/24 ✅
• Switch1 Fa0/24 ✅

👉 If one side is not connected → port stays DOWN

⚙️ 3. Enable Port (Just in case)

Run on BOTH switches:

• enable
• configure terminal
• interface fa0/24
• no shutdown

🔍 What Happens Internally?

• PC0 sends packet → Switch0
• Switch0 adds VLAN tag (802.1Q)
• Packet goes through trunk
• Switch1 reads VLAN tag
• Forwards to correct VLAN port

⚠️ Key Concepts (Very Important)

🔹 Access Port

Carries one VLAN only

🔹 Trunk Port

Carries multiple VLANs

🔹 VLAN Tagging

• Switch adds VLAN ID inside frame
• Helps identify which VLAN packet belongs to

⚠️ Common Mistakes

• ❌ VLAN not created on both switches
• ❌ Trunk not configured on both sides
• ❌ Wrong port numbers
• ❌ IP mismatch

❓ What protocol is used?

👉 IEEE 802.1Q

❓ Difference between access & trunk?

Access → single VLAN

Trunk → multiple VLANs

❓ Why trunking is needed?

👉 To connect multiple switches while maintaining VLAN separation

🧠 Real-World Example

Company has:

• Multiple floors
• Multiple switches

👉 VLANs must travel between switches

➡️ Trunking is used

NOTE - In Cisco Packet Tracer labs and real-world configurations, VLAN 99 is a common industry-standard placeholder used for two specific administrative purposes:

1. Management VLAN: It is frequently used to host the switch's Management IP address. By moving management traffic (SSH, Telnet, SNMP) to a dedicated VLAN like 99, you keep it separate from regular user data, which is a major security best practice.
2. Native VLAN: It is often designated as the Native VLAN on trunk links. The Native VLAN is responsible for handling all "untagged" traffic that passes through a trunk port.

Why use 10 and 20 instead of the default?

By default, Cisco switches use VLAN 1 for both management and native traffic. However, using the default is considered a security risk because:

1. VLAN Hopping: Attackers can exploit the default VLAN 1 to jump between different networks.
2. Control Traffic: Standard control protocols (like CDP or VTP) often use VLAN 1. Moving user and management data to a different ID like 99 prevents these streams from mixing.

Key Rules for VLAN 10 and 20

• Consistency: If you set VLAN 99 as the native VLAN on one switch, you must set it on the other side of the trunk as well. If they don't match, you will see a native VLAN mismatch error, which can cause connectivity issues.
• Logical ID: There is nothing "magic" about the number 99; it is just a common convention. You could technically use 100, 777, or any other valid ID.

✅ Why ping 192.168.10.2 WORKS

Because:

👉 PC0 and PC2 are in same VLAN (VLAN 10)

Even though they are on different switches:

• Trunk carries VLAN 10 traffic
• Switches forward frames based on MAC
• No routing needed

✔ So it works

❌ Why ping 192.168.20.2 FAILS from PC0

Because:

• 👉 PC0 is in VLAN 10
• 👉 PC3 is in VLAN 20

These are different networks

🔥 Simple Analogy (Very Important)

Think like this:

VLAN 10 = Room A

VLAN 20 = Room B

• 👉 Switch = hallway
• 👉 Trunk = connecting hallway between buildings

Case 1 (Working)

PC0 → PC2

Room A → Room A

✔ Allowed

Case 2 (Failing)

PC0 → PC3

Room A → Room B

❌ Door is closed (no router)

🎯 Core Rule

• 👉 Switch = Layer 2 → only works inside same VLAN
• 👉 Router = Layer 3 → required between VLANs

NOTE - Now the question is if “PC1 (192.168.20.1) is in same switch as PC0, so why not ping?”

• 👉 Same switch does NOT matter
• 👉 VLAN matters

So: 

Why ping between VLANs fails?

Answer:

Because switches operate at Layer 2 and cannot route traffic between different VLANs. Inter-VLAN routing requires a Layer 3 device like a router.

✅ What You Need to Do

To make this work:

👉 You must configure Inter-VLAN Routing so for this visit our another blog.

Disclaimer

VLAN (Virtual LAN) — Practical + Interview Guide

Definition (say this in interviews):

A VLAN (Virtual Local Area Network) is a logical segmentation of a Layer 2 network that separates devices into different broadcast domains on the same physical switch.

👉 In simple terms:

“Same switch, but different networks.”

🎯 What You Will Learn

• Network segmentation
• Broadcast isolation
• Basic switch configuration
• Real office network concept

🧪 Lab Setup (Build This in Cisco Packet Tracer)

🔹 Topology

• 1 Switch (2960)
• 4 PCs

🔹 VLAN Plan

⚙️ Step 1: Assign IP Addresses

• PC0 → 192.168.10.1
• PC1 → 192.168.10.2
• PC2 → 192.168.20.1
• PC3 → 192.168.20.2

Subnet mask: 255.255.255.0

⚙️ Step 2: Create VLANs on Switch

Go to Switch → CLI

enable
configure terminal

vlan 10
name HR

vlan 20
name IT

exit

⚙️ Step 3: Assign Ports to VLANs

Assume:

• PC0 → Fa0/1
• PC1 → Fa0/2
• PC2 → Fa0/3
• PC3 → Fa0/4

interface fa0/1
switchport mode access
switchport access vlan 10

interface fa0/2
switchport mode access
switchport access vlan 10

interface fa0/3
switchport mode access
switchport access vlan 20

interface fa0/4
switchport mode access
switchport access vlan 20

🧪 Step 4: Test Connectivity

✅ Same VLAN (Should Work)

From PC0:

ping 192.168.10.2

✔ Success

❌ Different VLAN (Should Fail)

From PC0:

ping 192.168.20.1

❌ Request timed out

🔍 What You Just Learned (IMPORTANT)

VLAN 10 and VLAN 20 are separate broadcast domains

Switch does NOT allow communication between VLANs

Even though:

• Same switch
• Same cable

👉 Still isolated

Simulation

⚠️ Common Mistakes

• ❌ Forgetting switchport mode access
• ❌ Wrong port mapping
• ❌ Same IP network for all PCs

🎯 Interview Questions (Must Know)

❓ What is VLAN?

👉 Logical segmentation of network at Layer 2.

❓ Why VLAN is used?

• Security
• Performance
• Broadcast control

❓ Can VLANs communicate?

👉 No, unless:

➡️ Inter-VLAN Routing is configured

❓ VLAN works on which layer?

👉 Layer 2 (Data Link)

🧠 Real-World Example

Office:

• HR department → VLAN 10
• IT department → VLAN 20

👉 They are isolated for:

• Security
• Traffic control

Disclaimer

Repeater Practical in Cisco Packet Tracer (Step-by-Step Guide)

In networking, maintaining signal strength over long distances is a fundamental challenge. This is where a repeater comes into play. In this practical, we will understand how a repeater works and simulate it using Cisco Packet Tracer.

📌 What is a Repeater?

A repeater is a networking device that operates at the Physical Layer (Layer 1) of the OSI model and in first port its getting signal and in second port regenerate the signal and send to the receiver.

Definition:

A repeater receives a weak or corrupted signal, regenerates it, and retransmits it to extend the network distance.

🔍 Key Features of Repeater

• Works on Layer 1 (Physical Layer)
• Does not understand IP or MAC addresses
• Only regenerates signals
• Used to extend network range
• Cannot filter or route data

🧪 Lab Overview (Your Topology)

From your setup:

• Two switches connected via a Repeater
• Each switch connects to multiple PCs

All devices are in the same network:

10.10.10.0/24

🖥️ IP Addressing

🎯 Objective

• Understand how a repeater extends network connectivity
• Enable communication between two switches
• Test connectivity between distant PCs
• Observe signal regeneration

🛠️ Step 1: Create Topology

Open Cisco Packet Tracer

Add:

• 2 Switches (2960)
• 1 Repeater
• 6 PCs
• Connect:
• PCs → Switches
• Switches → Repeater

👉 Use Copper Straight-Through Cable

🌐 Step 2: Configure IP Addresses

Assign IPs manually:

All PCs in same subnet: 10.10.10.0/24

Subnet mask: 255.255.255.0

👉 No default gateway needed (no router)

📡 Step 3: Test Connectivity

From PC0 → Command Prompt:

ping 10.10.10.6

👉 Expected Result:

✔ Successful reply

🎬 Step 4: Use Simulation Mode

• Switch to Simulation Mode
• Enable all filters
• Run ping again
• Click Auto Capture / Play

🔍 What Happens Internally?

1️⃣ Signal Travels from PC0

Data sent to Switch0

2️⃣ Repeater Regenerates Signal

Receives weak signal

Cleans and retransmits it

3️⃣ Signal Reaches Switch1

Delivered to destination PC (PC5)

⚠️ Important Observations

• Repeater does not filter traffic
• Entire network remains a single collision domain
• All devices share bandwidth

❌ Limitations of Repeater

• No intelligence (cannot make decisions)
• Cannot reduce network traffic
• Cannot improve security
• Rarely used in modern networks

🔄 Repeater vs Hub vs Switch

🧠 Real-World Use

Repeaters are used in:

• Long-distance cable networks
• Fiber optic communication
• Legacy Ethernet setups

👉 In modern networks, switches and routers have replaced repeaters.

💡 Conclusion

This practical demonstrates how a repeater helps extend network distance by regenerating signals. While it plays a foundational role in networking, it lacks intelligence and is rarely used today. Understanding repeaters builds a strong base for learning advanced networking devices like switches and routers.