📘Cisco DevNet Associate (200-901 DEVASC)
1. Switches
Function:
A switch is a networking device that connects multiple devices (like computers, servers, or access points) within the same network or local area network (LAN). It helps devices communicate with each other efficiently.
Key Points:
- Switches operate mainly at Layer 2 (Data Link Layer) of the OSI model. Some advanced switches can operate at Layer 3 (Network Layer).
- They use MAC addresses to send data to the correct device.
- Switches do not route traffic between different networks; they only forward traffic within the same network.
- They reduce network congestion by sending data only to the intended device rather than broadcasting to all devices.
Example in IT environment:
- A data center server rack has multiple servers connected to a switch. The switch ensures that traffic from one server goes only to the intended server, improving speed and security.
Advanced Note:
- Managed switches can have VLANs (Virtual LANs) to separate traffic logically within the same physical network.
2. Routers
Function:
A router connects different networks together and directs traffic between them. It decides the best path for data to travel from the source to the destination across networks.
Key Points:
- Routers operate at Layer 3 (Network Layer) of the OSI model.
- They use IP addresses to determine where to send data.
- Routers can connect a company’s internal network to the internet or connect multiple office branches over a WAN (Wide Area Network).
- They often have features like Network Address Translation (NAT) and Dynamic Host Configuration Protocol (DHCP).
Example in IT environment:
- An office network router connects the internal network to the internet. It routes traffic from employees’ computers to external websites and vice versa.
Exam Tip:
- Remember: Switch = internal communication, Router = between networks.
3. Firewalls
Function:
A firewall protects a network by controlling which traffic is allowed in or out based on security rules. It acts as a barrier between a trusted network and untrusted networks (like the internet).
Key Points:
- Firewalls can be hardware devices or software applications.
- They inspect traffic using IP addresses, ports, and protocols.
- Types of firewalls:
- Packet-filtering firewalls – check the header of each packet (basic filtering).
- Stateful firewalls – track active connections to allow or block traffic dynamically.
- Next-Generation Firewalls (NGFWs) – include intrusion detection, deep packet inspection, and application-level control.
Example in IT environment:
- A firewall allows company employees to access approved cloud services but blocks unauthorized access from the internet.
Exam Tip:
- Firewalls do not route traffic; they filter it.
4. Load Balancers
Function:
A load balancer distributes network or application traffic across multiple servers to ensure no single server becomes overwhelmed. This improves performance, reliability, and uptime.
Key Points:
- Load balancers can operate at Layer 4 (Transport Layer) for TCP/UDP traffic or Layer 7 (Application Layer) for HTTP/HTTPS traffic.
- They help scale applications horizontally by adding more servers behind them.
- Methods of distribution:
- Round-robin – traffic is sent sequentially to each server.
- Least connections – traffic is sent to the server with the fewest active connections.
- Weighted distribution – traffic is distributed based on server capacity.
Example in IT environment:
- A web application uses three servers. The load balancer ensures that incoming user requests are spread across all three servers evenly, preventing slowdowns or crashes.
Exam Tip:
- Load balancers improve availability and performance, unlike routers or switches, which primarily direct traffic.
Summary Table
| Component | Main Function | OSI Layer | Key Use Case in IT Environment |
|---|---|---|---|
| Switch | Connect devices within the same network | Layer 2 (some Layer 3) | Forward traffic between servers in a rack |
| Router | Connect different networks | Layer 3 | Connect internal network to internet |
| Firewall | Control and protect network traffic | Layer 3/4+ | Block unauthorized access to internal servers |
| Load Balancer | Distribute traffic across servers | Layer 4/7 | Ensure web application uptime and performance |
✅ Key Exam Tips:
- Switch vs Router: Remember switches are for local network traffic, routers are for network-to-network traffic.
- Firewall is security, not routing: It filters traffic; it doesn’t decide best paths.
- Load balancer is about performance and availability: It doesn’t store or secure data; it optimizes resource usage.
- Know the OSI layer each device primarily operates at; it’s often tested.
