Summary of Computer Networking: SRWE Exam Review
SRWE Exam Review: Master Computer Networking Essentials
Introduction
Network switches are fundamental components of Local Area Networks (LANs). They enable the connection of computers, printers, and other devices, manage data flow within the network, and ensure traffic isolation and management. This resource explores important switch functions and fundamental security practices that help protect the network.
What You Will Learn
- Basic modes and protocols related to switches
- Why segment a network and its benefits
- How to diagnose problems with interfaces
- Fundamentals of access authentication and scalable account management
- Practical examples and security recommendations
Definition: A switch is a network device that connects devices in a local network at the data link layer and forwards frames based on MAC addresses.
Switch Modes and Protocols
VTP — VLAN Trunking Protocol
- VTP is a protocol for synchronizing VLAN information between switches.
- It requires switches to operate in specific modes: Server or Client.
- Server mode: you can create, modify, and delete VLANs.
- Client mode: local VLAN changes are not permitted; the switch receives information from the server.
Definition: VTP is a protocol for centralized management of the VLAN database across a network.
DTP — Dynamic Trunking Protocol
- DTP controls trunk negotiation between two Cisco switches.
- Mode combinations that form a trunk:
- dynamic desirable – trunk (if the other side is trunk or dynamic desirable or dynamic auto)
- access – dynamic auto (does not initiate trunking)
- dynamic desirable – dynamic desirable (both sides initiate)
Table: DTP Negotiation Result
| Local Mode | Neighbor Mode | Result |
|---|---|---|
| dynamic desirable | trunk | trunk |
| dynamic desirable | dynamic auto | trunk |
| dynamic auto | dynamic auto | non-trunk (access) |
Why Segment a Network Using a Switch (Layer 2)
- Goals of Segmentation:
- Increase available bandwidth for users (enhance user bandwidth)
- Isolate traffic between segments (isolate traffic)
- What Segmentation DOES NOT Do:
- Does not reduce the number of broadcast domains (Layer 2 switches typically do not separate broadcast domains without VLANs)
- Does not create virtual circuits (virtual circuits)
Definition: Network segmentation divides a large network into smaller, logical parts for improved performance and security.
Interface Troubleshooting and Error Monitoring
- The
show interfacescommand (orshow interfaces switch) is used to:- Detect media errors (CRC, runts, giants)
- Determine if packets are being sent and received
- Identify issues with a specific connected device when packets are being dropped
- What this command DOES NOT directly provide:
- The device's MAC address (use
show mac address-tablefor this) - Remote reachability information (reachability issues are typically a matter of routing or gateway configuration)
- The device's MAC address (use
Definition: The diagnostic
show interfacescommand provides detailed statistics and error counters for physical and virtual interfaces.
Access Authentication: Local Database vs. AAA
- Local Database (user accounts stored locally on the device):
- Advantages: simple, enables auditing of logins on that specific device
- Main Disadvantage: accounts must be created individually on each device, which is not scalable
- AAA with Centralized Servers (RADIUS/TACACS+):
- Provides centralized account management and authorization
- Facilitates scalability and a unified access policy
Definition: AAA (Authentication, Authorization, Accounting) is a framework for user authentication, managing access rights, and logging activities.
802.1X port-based authentication (basic roles)
- Client (Supplicant): device requesting access
- Switch (Authenticator): controls physical access to the network based on the authentication resu
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Network Switches - Functions and Security
Klíčové pojmy: VTP requires Server and Client modes for VLAN synchronization., DTP negotiation depends on the combination of modes (dynamic desirable/initiate)., Layer 2 segmentation increases bandwidth and isolates traffic., The "show interfaces" command diagnoses CRC, runts, giants, and other interface errors., Local account databases are not scalable; use AAA for centralization., 802.1X defines the Client (Supplicant), Switch (Authenticator), and Authentication Server roles., Router-on-a-stick uses subinterfaces with "encapsulation dot1q <VLAN>" and configures the switch port as a trunk., On an L3 switch: create an SVI, enable IP routing, and assign ports to the appropriate VLANs., Utilize private VLANs and 802.1X to mitigate VLAN attacks., On trunks, allow only necessary VLANs to prevent misuse or unauthorized access.