Building a Local Office LAN with a Switch
Learn how to scale beyond direct cables by designing a star-topology Local Area Network. Connect multiple workstations to a centralized Layer 2 switch, configure static addressing across a shared /24 subnet, and learn how switches learn MAC addresses to forward frames without collisions.
Picture a small office floor with twenty engineers and managers. If you wanted every computer to share files directly with one another using point-to-point cables, you would need 190 separate wires running across the carpet and nineteen network cards installed into every single computer chassis. In networking mathematics, a direct mesh scales at N*(N-1)/2, quickly turning server closets into an impossible, expensive spiderweb of copper cabling.
To solve this physical scaling challenge, computer networks evolved into a Star Topology. Instead of running cables between individual computers, every workstation runs a single patch cable to a central traffic controller: a Layer 2 Network Switch. This single architectural shift laid the foundation for every modern enterprise local area network.
Building an enterprise office LAN requires analyzing physical star topology benefits, contrasting collision domains with microsegmentation, applying consistent IPv4 subnet addressing, and tracking how switches dynamically populate Content Addressable Memory tables from frame headers.
Network Architecture Plan
| Segment | Interface | Subnet / Address | Functional Role |
|---|---|---|---|
| Central Switch | FastEthernet0/1 - 0/4 | Layer 2 Switching | Central multi-port distribution hub |
| Workstation 1 | FastEthernet0 | 192.168.1.10/24 | Accounting Department Desktop |
| Workstation 2 | FastEthernet0 | 192.168.1.11/24 | Operations Department Desktop |
| Engineer Laptop | FastEthernet0 | 192.168.1.12/24 | Mobile Engineer Workstation |
Star Topology Network Architecture
In a star topology, each client endpoint connects directly to a dedicated physical port on a central network switch. This layout delivers massive operational advantages: if an employee disconnects their laptop or a cleaning crew damages an office drop cable, only that single workstation loses connectivity. The rest of the office continues printing, sharing files, and working without interruption.
Contrast this with legacy daisy-chain bus topologies, where a single loose terminator or damaged tap brought down every computer in the entire building. The star topology provides complete physical link isolation while keeping cabling clean, organized, and manageable inside a central patch panel rack.
On your Simneta NetLab workspace canvas, place a 24-Port Managed Access Switch in the center of the office area, and position three client computers around it: Workstation 1 (Accounting), Workstation 2 (Operations), and an Engineer Laptop.
Each device connects inward toward the central switch, creating a clean star formation that simplifies both physical troubleshooting and future expansion.
Star topologies completely isolate physical link failures. A damaged drop cable only affects that single workstation, leaving the rest of the enterprise local area network fully operational.
Collision Domains And Microsegmentation
Before modern switches existed, local offices connected computers using passive hardware devices called network hubs. Hubs were electrically unmanaged: whenever one computer transmitted data, the hub repeated those electrical pulses out of every other connected port simultaneously.
If two computers tried to speak at the exact same fraction of a millisecond, their electrical voltages collided on the wire, corrupting the packets and forcing both devices to back off and retransmit using CSMA/CD. As more computers joined the hub, collision rates soared and real network throughput ground to a halt.
A modern Layer 2 switch eliminates this bottleneck completely through microsegmentation. Every physical port on a switch forms its own independent collision domain operating in Full Duplex mode, allowing workstations to send and receive data simultaneously without electrical interference.
When you connect Workstation 1 (port 1), Workstation 2 (port 2), and the Engineer Laptop (port 3) using standard Cat6 Straight-Through cables, each machine receives dedicated, collision-free 100 Mbps or 1 Gbps bandwidth.
Observe the link status indicator triangles along the cables turn solid green as the switch network ports detect electrical carrier signals and bring the physical links UP.
Real-world field incident: An intern once plugged an old 5-port hub under a desk to connect a printer, causing half the accounting team to experience 40% packet drops due to collision backoffs until the hub was replaced with an unmanaged switch.
Configuring Local Subnet Addresses
A Layer 2 switch operates at the data-link layer, moving raw Ethernet frames between physical ports. However, for operating system applications to exchange meaningful data, all devices connected to the switch must share a common logical Layer 3 addressing scheme.
We assign private RFC 1918 addresses from the 192.168.1.0/24 subnet. Click each machine on your canvas to open its network settings or enter its terminal command line.
Workstation 1 receives 192.168.1.10 with subnet mask 255.255.255.0. Workstation 2 receives 192.168.1.11, and the Engineer Laptop receives 192.168.1.12.
The subnet mask 255.255.255.0 translates to 24 consecutive binary ones (`/24`). The first three octets (`192.168.1`) identify the shared network ID, while the final octet identifies the unique host on that physical segment.
Because all three computers share the exact same network ID, each machine recognizes that its neighbors live on the local wire, allowing them to communicate directly without needing a router gateway.
# On Workstation 1 (Accounting)
PC-1> ip 192.168.1.10/24 192.168.1.1
Checking for duplicate IP address...
PC-1: 192.168.1.10 255.255.255.0 gateway 192.168.1.1
# On Workstation 2 (Operations)
PC-2> ip 192.168.1.11/24 192.168.1.1
Checking for duplicate IP address...
PC-2: 192.168.1.11 255.255.255.0 gateway 192.168.1.1
# On Engineer Laptop
Laptop> ip 192.168.1.12/24 192.168.1.1
Checking for duplicate IP address...
Laptop: 192.168.1.12 255.255.255.0 gateway 192.168.1.1Breaking down the client static IP configuration commands:
ip 192.168.1.10/24 192.168.1.1: Assigns the IPv4 address, applies a 24-bit subnet mask, and points to the anticipated default gateway.Checking for duplicate IP address...: The operating system broadcasts a gratuitous ARP probe on the switch network to confirm no other workstation already claims this IP address before bringing the interface active.Subnet rule: Devices connected to the same Layer 2 switch must share the exact same network prefix and subnet mask to communicate locally. If one machine had a /25 mask and another had a /24, communication would fail without a router.
Dynamic MAC Address Learning
When you first power on a switch, its internal memory is completely blank. The switch does not know which computer is plugged into which physical port.
Open the terminal on Workstation 1 and ping Workstation 2 by typing ping 192.168.1.11. Here is the step-by-step process that takes place inside the hardware:
First, Workstation 1 does not know the hardware MAC address of Workstation 2. It broadcasts an Address Resolution Protocol (ARP) request: Who has 192.168.1.11? Tell 192.168.1.10.
As that frame enters Port 1, the switch inspects the Source MAC Address inside the Ethernet header. It immediately writes an entry into its internal table: MAC address 0050.7966.6801 is located on Port FastEthernet0/1.
Because the destination MAC is a broadcast (`FF:FF:FF:FF:FF:FF`), the switch floods the frame out of Ports 2 and 3. Workstation 2 receives the ARP request, recognizes its own IP, and sends a unicast ARP reply directly back to Workstation 1.
When that reply enters Port 2, the switch learns its second entry: MAC address 0050.7966.6802 is located on Port FastEthernet0/2.
From this exact moment forward, any packet sent between Workstation 1 and Workstation 2 is forwarded directly between Ports 1 and 2 in pure unicast mode, completely invisible to the Engineer Laptop on Port 3.
Switch forwarding logic: A switch learns dynamically by examining the SOURCE MAC address of every arriving frame, but it forwards frames by looking up the DESTINATION MAC address in its CAM table.
Analyzing MAC Address Tables
Open the CLI console on the central switch and execute the command show mac address-table to verify how frame inspection populated switch memory after our ping tests.
Analyzing the MAC address table columns:
DYNAMIC, meaning the switch learned these addresses passively from incoming packets. If a device stops transmitting for 300 seconds (the default aging timer), the switch purges the record to free memory.CAM aging timer: Switches hold dynamic MAC table entries for 300 seconds (5 minutes) by default. If a workstation moves to a different office port, the switch updates the port mapping as soon as the workstation transmits its next frame.
Related Network Labs
Continue your network simulation practice with these recommended labs.
Setting Up a Local Web Server
VLAN Trunking with 802.1Q
Preventing Loops with Spanning Tree
Securing Switch Ports with Port Security
Bundling Switch Uplinks with LACP EtherChannel
Inter-VLAN Routing with Router-on-a-Stick
Dynamic Routing with Single-Area OSPF
Gateway Redundancy with HSRP Failover
Filtering Traffic with Extended ACLs
Connecting LAN to Internet with NAT
Resolving Domain Names with Local DNS
Stopping Rogue DHCP with Snooping
Connecting Two Switches with an Access Uplink
Configuring Static IP on Workstation
Testing Reachability and Latency with Ping
Inspecting ARP Cache Tables
Setting Up DHCP Static Reservations
Connecting Routers with /30 Subnet
Configuring Default Static Route to ISP
Blocking Ping with Standard ACL
Port Forwarding for Web Servers
Fixing Default Gateway Misconfigurations
Discussion & Community Notes
Ask questions, share configuration tips, or discuss this laboratory topology.