Before diving into switch specifics, let's ground ourselves in the OSI model where:

• Layer 2 (Data Link): Operates with MAC addresses (e.g., 00:1A:2B:3C:4D:5E)
• Layer 3 (Network): Handles IP addresses (e.g., 192.168.1.1)

A pure L2 switch builds MAC address tables for forwarding decisions. Here's what happens under the hood:

# Sample MAC address table in a Cisco switch
Switch# show mac address-table
          Mac Address Table
-------------------------------------------
Vlan    Mac Address       Type        Ports
----    -----------       --------    -----
   1    0050.0f12.3456    DYNAMIC     Gi0/1
   1    0001.c972.abc1    DYNAMIC     Gi0/2

Key limitations:
- Cannot route between subnets
- Broadcast domain constraints
- No IP awareness beyond basic VLAN tagging

An L3 switch combines switching with routing functionality. Example routing table:

# Cisco L3 switch routing table example
Switch# show ip route
Codes: C - connected, S - static, R - RIP
       O - OSPF, IA - OSPF inter area

Gateway of last resort is 10.1.1.1 to network 0.0.0.0

C    192.168.1.0/24 is directly connected, Vlan10
C    192.168.2.0/24 is directly connected, Vlan20
S*   0.0.0.0/0 [1/0] via 10.1.1.1

Choose Layer 2 when:
- Building access layer networks
- Needing simple VLAN segmentation
- High-density port requirements

Opt for Layer 3 when:
- Inter-VLAN routing is needed
- Implementing network segmentation
- Reducing router bottlenecks

Basic L2 VLAN setup:

vlan 10
 name Engineering
!
interface GigabitEthernet0/1
 switchport mode access
 switchport access vlan 10

L3 Switch Inter-VLAN routing:

interface Vlan10
 ip address 192.168.10.1 255.255.255.0
!
interface Vlan20
 ip address 192.168.20.1 255.255.255.0
!
ip routing

Modern L3 switches often include:
- ACLs with Layer 3/4 filtering
- QoS policies based on DSCP
- VRF-lite for multi-tenancy
- DHCP relay functionality

# Example ACL for inter-VLAN traffic control
access-list 110 permit tcp 192.168.10.0 0.0.0.255 
    192.168.20.0 0.0.0.255 eq www
access-list 110 deny ip any any
!
interface Vlan10
 ip access-group 110 in

When working with network infrastructure, understanding the difference between Layer 2 and Layer 3 switches is crucial. These devices operate at different layers of the OSI model and serve distinct purposes in network architecture.

A Layer 2 switch operates at the Data Link layer (Layer 2) of the OSI model. It uses MAC addresses to forward frames between devices on the same network segment. Here's a simple example of how a Layer 2 switch might be configured:

# Basic VLAN configuration on a Layer 2 switch
vlan 10
 name Engineering
exit
interface FastEthernet0/1
 switchport mode access
 switchport access vlan 10

Layer 3 switches add routing functionality at the Network layer (Layer 3). They can make forwarding decisions based on IP addresses, enabling inter-VLAN routing without needing a separate router. Here's an example configuration:

# Enabling inter-VLAN routing on a Layer 3 switch
interface Vlan10
 ip address 192.168.10.1 255.255.255.0
!
interface Vlan20
 ip address 192.168.20.1 255.255.255.0
!
ip routing

Layer 3 switches typically have higher forwarding rates than routers because they use specialized hardware (ASICs) for routing decisions. This makes them ideal for:

• High-performance data center networks
• Campus network backbones
• Enterprise core networks

For simple network segmentation within a single subnet, a Layer 2 switch is sufficient. However, when you need to route between multiple subnets or VLANs while maintaining high throughput, a Layer 3 switch becomes essential.

Consider a scenario where you need to connect multiple departments in an office building:

# Sample network design using both switch types
# Layer 3 switch at core
interface Vlan10  # HR
 ip address 10.0.10.1/24
!
interface Vlan20  # Engineering
 ip address 10.0.20.1/24
!
# Layer 2 switches at access layer
interface GigabitEthernet1/0/1
 switchport mode access
 switchport access vlan 10
!
interface GigabitEthernet1/0/2
 switchport mode access
 switchport access vlan 20

When developing network applications, understanding these differences affects how you:

• Design network topologies
• Implement traffic shaping
• Configure monitoring tools
• Optimize packet flows

For instance, when writing a network monitoring script, you might need different approaches for Layer 2 vs Layer 3 devices:

# Python example: Checking switch type
def check_switch_type(device):
    if device.supports_ip_routing:
        print("This is a Layer 3 switch")
        # Implement Layer 3 specific checks
    else:
        print("This is a Layer 2 switch")
        # Implement Layer 2 specific checks