switch-trunking lab in Cisco Packet Tracer

We can recreate this exact switch-trunking lab in Cisco Packet Tracer. The key concept is:

Access ports connect end devices to one VLAN. Trunk port carries multiple VLANs between switches.

One small correction in the image: the SW2 configuration appears to show vlan 18 and vlan 38, but based on the topology it should be VLAN 10, 20, and 30.

why a company needs trunking.

Let's forget Packet Tracer for a moment and look at an actual corporate office.

Imagine your Cubic office

Suppose an office has 200 employees and one switch has 48 ports.
The company doesn't want every device to be in the same network.

They may create:

• VLAN 10 → Employees
• VLAN 20 → IT/Servers
• VLAN 30 → Guest Wi-Fi
• VLAN 40 → CCTV
• VLAN 50 → Voice/IP Phones

So physically you might have:

Now comes the important question:

Why do we need a TRUNK?

Imagine SW1 and SW2 are on different floors.

But users on both floors need access to the same VLANs.

For example:

 
SW1                          SW2

Employee VLAN 10 ─────────── VLAN 10
IT VLAN 20      ─────────── VLAN 20
Guest VLAN 30   ─────────── VLAN 30
Voice VLAN 40   ─────────── VLAN 40

Do we need four physical cables?

SW1 ================= SW2   VLAN 10

SW1 ================= SW2   VLAN 20

SW1 ================= SW2   VLAN 30

SW1 ================= SW2   VLAN 40

That would be inefficient.

Instead, we use one trunk link:

That's the main reason for trunking.

1. Create the topology

In Packet Tracer, add:

2 × 2960 switches
4 × PCs


Arrange them:  

 More precisely:

Connections

     
 Device	   Port	               Device	     Port	Type
  PC1	   FastEthernet0	SW1	     Fa0/1	Copper Straight-Through
  PC2	   FastEthernet0	SW1	     Fa0/2	Copper Straight-Through
  SW1	   Fa0/24	        SW2          Fa0/24	Copper Cross-Over*
  PC3	   FastEthernet0	SW2	     Fa0/1	Copper Straight-Through
  PC4	   FastEthernet0	SW2	     Fa0/2	Copper Straight-Through


                         www.kumaratuljaiswal.in

2. Create VLANs on SW1

Click SW1 → CLI. 

enable
configure terminal

vlan 10
name VLAN10
exit

vlan 20
name VLAN20
exit

vlan 30
name VLAN30
exit

So SW1 now has:

• VLAN 10
• VLAN 20
• VLAN 30 

3. Configure PC1 port as VLAN 10

PC1 is connected to SW1 Fa0/1.


This means:

interface fa0/1
switchport mode access
switchport access vlan 10
exit

  

4. Configure PC2 port as VLAN 20

interface fa0/2
switchport mode access
switchport access vlan 20
exit

5. Configure SW1-to-SW2 as a trunk

This is the most important part.

On SW1: 

interface fa0/24
switchport mode trunk
switchport trunk allowed vlan 10,20
exit

Notice:

allowed vlan 10,20

We are not allowing VLAN 30.

Therefore:

• VLAN 10 → Allowed
• VLAN 20 → Allowed
• VLAN 30 → Blocked 

6. Configure SW2

Go to SW2 → CLI.

Create the same VLANs:
 

enable
configure terminal

vlan 10
name VLAN10
exit

vlan 20
name VLAN20
exit

vlan 30
name VLAN30
exit

7. Configure PC3 as VLAN 10

PC3 is connected to SW2 Fa0/1:
 

interface fa0/1
switchport mode access
switchport access vlan 10
exit

8. Configure PC4 as VLAN 20

interface fa0/2
switchport mode access
switchport access vlan 20
exit

9. Configure SW2 trunk 

interface fa0/24
switchport mode trunk
switchport trunk allowed vlan 10,20
exit

Now both sides of the trunk agree: 

SW1 Fa0/24
      ||
      ||  802.1Q TRUNK
      ||
SW2 Fa0/24


Allowed VLANs:
10
20

VLAN 30:
NOT ALLOWED 

10. Configure PC IP addresses

Go to each PC:

PC → Desktop → IP Configuration


PC1

• IP Address: 192.168.10.10
• Subnet Mask: 255.255.255.0

PC2

• IP Address: 192.168.20.10
• Subnet Mask: 255.255.255.0

PC3

• IP Address: 192.168.10.20
• Subnet Mask: 255.255.255.0

PC4

• IP Address: 192.168.20.20
• Subnet Mask: 255.255.255.0

You don't need a default gateway for this particular lab because we're only testing Layer-2 communication within the same VLAN.

11. Test the important part

From PC1:

• ping 192.168.10.20

Expected:

• Reply from 192.168.10.20

Why? 

PC1
VLAN 10
   ↓
SW1
   ↓
TRUNK
   ↓
SW2
   ↓
VLAN 10
   ↓
PC3

So PC1 → PC3 should work.

Now from PC2:

ping 192.168.20.20

Expected:

Reply from 192.168.20.20

Because both are VLAN 20. 

12. Test between different VLANs


From PC1:

ping 192.168.20.20

This should fail.

Why?

PC1 → VLAN 10
             X
         VLAN 20

A Layer-2 switch does not route between VLAN 10 and VLAN 20. You would need a router or Layer-3 switch for inter-VLAN routing.

13. Verify the VLANs

On SW1:

• show vlan brief

You should see something similar to:

VLAN Name       Status    Ports

10   VLAN10     active    Fa0/1
20   VLAN20     active    Fa0/2
30   VLAN30     active

On SW2:

• show vlan brief

10   VLAN10     active    Fa0/1
20   VLAN20     active    Fa0/2
30   VLAN30     active  
  

  
| Test          | Expected                              |
| ------------- | ------------------------------------- |
| PC1 → PC3     | ✅ Works — same VLAN 10                |
| PC2 → PC4     | ✅ Works — same VLAN 20                |
| PC1 → PC2/PC4 | ❌ Fails — different VLANs, no routing |