Accurate and complete documentation is essential for monitoring, maintaining, and troubleshooting a network. A useful documentation set normally includes:
Physical and logical topology diagrams
Device inventories and configuration records
Addressing, VLAN, routing, and security information
Performance baselines
Cloud and remote-access services
Documentation should be stored in a controlled location, backed up, reviewed regularly, and updated whenever the network changes.
1.2.2 Network Types and Descriptions
Networks vary in size and purpose according to organizational requirements.
PAN — Personal Area Network
A PAN connects devices close to one person, often through Bluetooth. Its range is normally limited to a few meters.
LAN — Local Area Network
A LAN connects devices in a limited geographic area, such as a home, office, school, or small building. It commonly uses Ethernet and Wi-Fi.
WLAN — Wireless Local Area Network
A WLAN is a LAN that uses wireless connections. It provides mobility inside the coverage area without requiring a physical cable between each endpoint and the network.
WAN — Wide Area Network
A WAN connects networks over large geographic distances. The Internet is the best-known example. WAN services may use dedicated circuits, carrier networks, satellite links, or fiber-optic infrastructure.
MAN — Metropolitan Area Network
A MAN covers a metropolitan area. It is larger than a typical LAN but smaller than a WAN and may connect several LANs throughout a city.
VPN — Virtual Private Network
A VPN creates an encrypted tunnel across an untrusted or public network. It is commonly used to provide secure remote access to organizational resources or to connect sites securely.
Combined Example
1.2.3 Activity — Identify the Network Type
Description
Network Type
A network that spans a city
MAN
A LAN that connects devices wirelessly
WLAN
Connects devices close to one user, usually through Bluetooth
PAN
Wireless access points connect to extend wireless coverage
WMN
Connects networks over a large geographic distance, such as the Internet
WAN
Lets users connect securely to another network through an untrusted network
VPN
Usually uses copper cabling to connect devices to a switch in a small area
LAN
Groups users according to administratively defined boundaries instead of physical location
VLAN
1.2.4 Enterprise Network Topologies
The two main forms of network topology documentation are physical and logical diagrams.
A physical topology shows device locations, rooms, racks, ports, cabling, and physical connections.
A logical topology shows interfaces, Layer 3 addressing, subnets, VLANs, routing relationships, and logical paths.
Physical Topology
The following example identifies the physical location and function of devices in a small network.
Logical Topology
The logical topology for the same network includes interface names and the Layer 3 addressing plan.
A higher-level enterprise diagram may show cloud resources, headquarters, branch offices, and remote users connected through a VPN.
A real organization may maintain separate diagrams for:
Physical layout and connections
IP addressing and VLAN plans
Security controls and VPNs
Cloud services and management
Routing policies
Remote-access policies
1.2.5 Cloud Network Services and Applications
Core Service Models
SaaS — Software as a Service: Ready-to-use software delivered through the Internet, such as Google Docs
PaaS — Platform as a Service: A managed platform for developing and deploying applications
IaaS — Infrastructure as a Service: Virtualized compute, storage, and networking resources
XaaS — Anything as a Service
Additional service models include:
DRaaS: Disaster Recovery as a Service
CaaS: Containers as a Service
MaaS: Monitoring as a Service
DaaS: Desktop as a Service
SaaS Examples
Google Docs: Online document editing and collaboration
Microsoft 365: Microsoft's cloud productivity suite
Wireless systems use licensed and unlicensed portions of the electromagnetic spectrum. Wi-Fi technologies operate in unlicensed spectrum, although regulation and permitted channel use vary by country.
The IEEE 802.11 standards define how radio frequencies are used for Wi-Fi communication.
Standard
Frequency
Main Characteristics
802.11
2.4 GHz
Up to 2 Mbps
802.11a
5 GHz
Up to 54 Mbps; shorter range than 2.4 GHz systems
802.11b
2.4 GHz
Up to 11 Mbps; better obstacle penetration
802.11g
2.4 GHz
Up to 54 Mbps; backward-compatible with 802.11b
802.11n
2.4/5 GHz
Approximately 150–600 Mbps; supports MIMO
802.11ac
5 GHz
Approximately 450 Mbps–1.3 Gbps; supports multiple antennas
802.11ax
2.4/5 GHz
Higher efficiency and capacity; theoretical rates up to about 10 Gbps
MIMO, or Multiple-Input Multiple-Output, uses multiple antennas to improve throughput and reliability.
1.2.7 Packet Tracer — Connect a Network from a Diagram
This practical activity requires connecting devices according to a physical network topology and verifying that the final cabling matches the diagram.
1.2.8 Network Device Documentation
Accurate, current device documentation makes a network easier to manage and troubleshoot. It may include hardware, software, ownership, location, interfaces, addresses, serial numbers, operating-system versions, warranties, and configuration backups.
Organizations often use inventory systems, databases, tables, or spreadsheets.
Router Example
Field
Example
Device name
R1
Location
Server room
IP address
192.168.1.1
Operating-system version
IOS 15.4
LAN Switch Example
Field
Example
Device name
SW-CORE-01
Port count
48
Configured VLANs
10, 20, 30
Endpoint Example
Field
Example
Type
Desktop
User
Alex Smith
MAC address
00:1A:2B:3C:4D:5E
Update the documentation immediately after an approved network change. Outdated documentation can make troubleshooting slower and riskier.
1.2.9 Establishing a Network Baseline
A network baseline describes normal performance under expected operating conditions. It gives administrators a reference for distinguishing normal variation from a fault or capacity problem.
Monitoring Objective
Compare current network behavior with a predefined baseline.
Establishing the Baseline
Identify critical devices, interfaces, services, and time periods
Collect representative performance data
Record normal ranges and alert thresholds
Repeat measurements at different times and business cycles
Review the baseline after major network or workload changes
A useful baseline should answer questions such as:
What does performance look like on a normal day?
Where do most errors occur?
Which links and devices are most or least utilized?
Which devices should be monitored, and what thresholds should generate alerts?
Does the network operate according to the documented policies?
Why a Baseline Matters
Distinguishes abnormal behavior from expected behavior
Reveals hidden problems and underused resources
Supports capacity planning
Provides evidence when evaluating a troubleshooting change
Helps determine whether the current design can meet future business requirements
Without a baseline, there is no reliable reference for evaluating traffic, congestion, error rates, latency, or resource utilization.
1.2.10 Cisco Discovery Protocol Overview
Cisco Discovery Protocol (CDP) is a Cisco-proprietary Layer 2 protocol that discovers directly connected Cisco devices.
Main Characteristics
Independent of the upper-layer network protocol
Available on many Cisco routers, switches, servers, phones, and other devices
Sends periodic advertisements to directly connected neighbors
Shares information such as device identity, platform, capabilities, and interfaces
Uses
Discovering network topology
Troubleshooting connectivity and cabling
Reconstructing documentation when information is incomplete
Building a logical map of directly connected Cisco devices
CDP helps answer a basic operational question: “Which Cisco devices are directly connected, and through which interfaces?”
1.2.11 Discovering Devices with CDP
Assume the administrator knows only that R1 is connected to another device.
When CDP is enabled, show cdp neighbors reveals directly connected Cisco neighbors.
CDP
1R1# show cdp neighbors
2Capability Codes: R - Router, T - Trans Bridge, B - Source Route Bridge
3 S - Switch, H - Host, I - IGMP, r - Repeater, P - Phone,
4 D - Remote, C - CVTA, M - Two-port Mac Relay
5
6Device ID Local Intrfce Holdtme Capability Platform Port ID
7S1 Gig 0/0/1 179 S I WS-C3560- Fas 0/5
The output provides useful information about each neighbor:
Device ID: The neighboring device name, such as S1
Local Interface: The interface on the current device, such as G0/0/1
Port ID: The remote device interface, such as F0/5
Capability: Whether the neighbor is a router, switch, phone, or another device type
Platform: The neighbor's hardware model
The output shows that Cisco switch S1 is connected to R1 from R1 interface G0/0/1 to S1 interface F0/5.
Use show cdp neighbors detail to obtain more information, including the management IP address.
