Practical 3: Enterprise Cabling, Fiber Backbones & OSI PDU Analysis

• Select the correct medium — straight-through, crossover, fiber, coaxial and wireless — for every link in an enterprise topology.
• Perform physical hardware expansion by installing Gigabit Fiber PT-SWITCH-NM-1FGE SFP modules into modular Switch-PT switches.
• Configure fiber switch interfaces from the Cisco IOS CLI using speed, duplex and description commands.
• Use Simulation Mode with ICMP/ARP filters to inspect the PDU Information window and observe encapsulation at OSI Layers 1, 2 and 3.
• Explain why Layer 3 IP addresses stay constant end-to-end while Layer 2 MAC addresses are rewritten at each routed hop.
• Run advanced diagnostics — ipconfig /all, arp -a, ping and tracert — and interpret hop count and latency across the fiber backbone.

Focus: build the two-building campus, address the hosts, and wire every local link with the correct copper or wireless connection.

Step 1.1 — Create the File & Add Devices

Open Cisco Packet Tracer, create a new file, and add the devices below. Right-click each device → Edit Device Label to rename it exactly as shown.

Building A — Main Office

• 1 Switch (Switch-PT) → Switch-A
• 2 PCs (PC-PT) → Admin-PC, Sales-PC
• 1 Printer (Printer-PT) → Office-Printer
• 1 Router (2811) → Campus-Gateway
• 1 Server (Server-PT) → Corporate-NAS (this lives in a protected Server Farm behind the router)

Building B — Engineering Lab

• 1 Switch (Switch-PT) → Switch-B
• 2 PCs (PC-PT) → Eng-PC-1, Eng-PC-2
• 1 Access Point (AP-PT) → Eng-AP
• 1 Tablet (Tablet-PT) → Eng-Tablet

Step 1.2 — Arrange the Workspace

Position the devices into two clear zones so the topology reads left-to-right:

• Left = Building A: Admin-PC, Sales-PC and Office-Printer clustered around Switch-A; Campus-Gateway to the right of Switch-A; Corporate-NAS on its own, connected only to the router (Server Farm).
• Right = Building B: Eng-PC-1 and Eng-PC-2 around Switch-B; Eng-AP beside Switch-B with Eng-Tablet floating nearby.
• Leave an obvious gap between the two switches — this is where the 850 m fiber backbone will go in Phase 2.

Step 1.3 — Assign Static IP Addresses

The campus uses two subnets. Set static addresses on each end device via Desktop → IP Configuration (or Config → Settings). Configure the router interfaces via the CLI or the Config tab.

Router Interface CLI Configuration

Unlike switches, Cisco router ports are turned OFF (shutdown) by default. Open Campus-Gateway → CLI tab and enter the following commands to configure IP addresses and bring the interfaces up:

Router> enable
Router# configure terminal
Router(config)# hostname Campus-Gateway
Campus-Gateway(config)# interface FastEthernet0/0
Campus-Gateway(config-if)# ip address 192.168.10.1 255.255.255.0
Campus-Gateway(config-if)# no shutdown
Campus-Gateway(config-if)# exit
Campus-Gateway(config)# interface FastEthernet0/1
Campus-Gateway(config-if)# ip address 192.168.20.1 255.255.255.0
Campus-Gateway(config-if)# no shutdown
Campus-Gateway(config-if)# end
Campus-Gateway# copy running-config startup-config

Step 1.4 — Wire the Copper Links

Open the Connections palette and choose the correct cable for each link.

Straight-Through (dissimilar devices)

Use Copper Straight-Through (solid black line icon) for connecting hosts to switches, and switches to routers:

1. Admin-PC (Fa0) → Switch-A (Fa0/1)
2. Sales-PC (Fa0) → Switch-A (Fa0/2)
3. Office-Printer (Fa0) → Switch-A (Fa0/3)
4. Switch-A (Fa0/4 or Gig0/1) → Campus-Gateway (Fa0/0)
5. Eng-PC-1 (Fa0) → Switch-B (Fa0/1)
6. Eng-PC-2 (Fa0) → Switch-B (Fa0/2)
7. Eng-AP (Port0) → Switch-B (Fa0/3)

Crossover (similar / end-to-end devices)

1. Select Copper Crossover (dashed black line).
2. Campus-Gateway (Fa0/1) → Corporate-NAS (Fa0)

Do not connect Switch-A to Switch-B yet — that backbone is built with fiber in Phase 2.

Step 1.5 — Configure the Wireless Link

1. Click Eng-AP → Config tab → Port 1 (Wireless) and set the SSID to ENG-LAB.
2. Click Eng-Tablet → Config tab → Wireless0.
3. Set its SSID to ENG-LAB (case-sensitive — it must match the AP exactly).
4. Confirm the tablet still has the static IP 192.168.10.52.
5. Close the panel. A dotted line should appear between the Tablet and the AP, confirming association.

Focus: install fiber SFP modules into both switches, run the 850 m fiber backbone, and bring the interfaces up from the Cisco IOS CLI.

Copper UTP is limited to 100 metres because of signal attenuation and crosstalk. Building A and Building B are 850 metres apart, so the backbone must be fiber optic. To carry fiber, each Switch-PT generic switch needs a Gigabit fiber transceiver module installed.

Step 2.1 — Install the Fiber SFP Modules

Repeat this on both Switch-A and Switch-B:

1. Click the switch to open its configuration window and go to the Physical tab.
2. Click the power button on the switch chassis to turn it OFF. The interface lights go dark.
3. In the Modules list on the left, select PT-SWITCH-NM-1FGE (1-port Gigabit Ethernet fiber module).
4. Drag the module into the empty slot on the right of the switch. It seats as interface GigabitEthernet0/2 (a fiber port with a round connector).
5. Click the power button again to turn the switch back ON.
6. Close the window and repeat for the other switch.

Step 2.2 — Run the Fiber Backbone Cable

1. In the Connections palette, select Fiber (the orange/dashed cable icon).
2. Click Switch-A and choose its new fiber port GigabitEthernet0/2.
3. Click Switch-B and choose its fiber port GigabitEthernet0/2.
4. Using Place Note, label the link 850 m Single-Mode Fiber Backbone.

Step 2.3 — Configure the Fiber Interfaces via IOS CLI

Fiber transceivers often need speed and duplex set manually because optical auto-negotiation is inconsistent between vendors. Open Switch-A → CLI tab and enter:

Switch> enable
Switch# configure terminal
Switch(config)# hostname Switch-A
Switch-A(config)# interface GigabitEthernet0/2
Switch-A(config-if)# description Inter-Building Fiber Backbone Link
Switch-A(config-if)# speed 1000
Switch-A(config-if)# duplex full
Switch-A(config-if)# no shutdown
Switch-A(config-if)# end
Switch-A# copy running-config startup-config

Now repeat on Switch-B — both ends must match in speed and duplex or the link will stay down:

Switch> enable
Switch# configure terminal
Switch(config)# hostname Switch-B
Switch-B(config)# interface GigabitEthernet0/2
Switch-B(config-if)# description Inter-Building Fiber Backbone Link
Switch-B(config-if)# speed 1000
Switch-B(config-if)# duplex full
Switch-B(config-if)# no shutdown
Switch-B(config-if)# end
Switch-B# copy running-config startup-config

Step 2.4 — Add the Internet Uplink (Coax)

The campus also needs an internet feed, which introduces a third medium — coaxial. This mirrors the module-install skill from Step 2.1 but on the router.

1. Add a Cable Modem (Cable-Modem-PT) labelled Cable-Modem and a Cloud (Cloud-PT) labelled Internet-ISP near Building A.
2. Open Campus-Gateway → Physical tab, power it OFF, and drag a WIC-1ENET module into an empty WIC slot. Power it back ON.
3. With Copper Straight-Through, connect Campus-Gateway (Ethernet0/0/0) → Cable-Modem (Port1).
4. Select Coaxial and connect Cable-Modem (Port0) → Internet-ISP (Coaxial7).
5. Label the coax link Coaxial — Cable Broadband.

Focus: slow time down in Simulation Mode and watch a packet get encapsulated, switched, routed and re-framed across four different media.

Every message on a network is wrapped in headers as it travels down the OSI stack at the sender and unwrapped as it travels up the stack at the receiver. Simulation Mode lets you freeze a packet at each device and read those headers in the PDU Information window.

The OSI Encapsulation Stack

As data descends the stack, each layer adds its own header (the PDU). Layers 1–3 are the focus of this lab:

Step 3.1 — Enter Simulation Mode & Set Filters

1. Click the Simulation tab in the bottom-right corner (or press Shift + S).
2. In the Simulation Panel, click Edit Filters.
3. Click Show All / None to clear everything, then tick only ICMP and ARP.

Step 3.2 — The Switched Path (UTP → Fiber → UTP)

First trace a packet that stays inside the campus LAN and crosses the fiber backbone.

1. Select the Add Simple PDU (closed envelope) tool from the right toolbar.
2. Click Admin-PC (source), then click Eng-PC-1 (destination).
3. Click Capture / Forward repeatedly to step the packet one hop at a time. Watch it travel:
   Admin-PC → Switch-A → (fiber) → Switch-B → Eng-PC-1.
4. At each device, click the coloured envelope to open the PDU Information window and inspect the OSI Model, Inbound PDU Details and Outbound PDU Details tabs.

What to observe

• Layer 1 (Physical): Leaving Admin-PC the bits are electrical signals on copper. On the Switch-A → Switch-B backbone they become pulses of light in glass, then convert back to electrical on the Switch-B → Eng-PC-1 copper link. The bits are identical — only the physical encoding changes.
• Layer 2 (Data Link): Because this whole path is switched (no router crossed), the Ethernet II frame keeps the same Source MAC (Admin-PC) and Destination MAC (Eng-PC-1) from end to end. Switches forward the frame unchanged — they never rewrite MAC addresses.
• Layer 3 (Network): Source IP 192.168.10.10 and Destination IP 192.168.10.50 stay constant.

Step 3.3 — The Routed Path (MAC Rewrite at Layer 2)

Now trace a packet that crosses the router into the Server Farm subnet.

1. Add a Simple PDU from Admin-PC (source) to Corporate-NAS (destination 192.168.20.5).
2. Step it through: Admin-PC → Switch-A → Campus-Gateway → Corporate-NAS.
3. Open the PDU Information window at the Campus-Gateway router and compare the Inbound vs Outbound Ethernet headers.

What to observe at the router

• Layer 3 (Network): Source IP 192.168.10.10 and Destination IP 192.168.20.5 are unchanged — the IP addresses identify the original endpoints and never change as the packet is routed.
• Layer 2 (Data Link) — the rewrite: On the way in, the frame's Destination MAC is the router's Gig0/0 interface. On the way out, the router builds a brand-new frame: Source MAC becomes the router's Gig0/1 interface, and Destination MAC becomes Corporate-NAS. MAC addresses are rewritten on every routed link.
• ARP in action: Notice the earlier ARP exchange — Admin-PC first ARPs for its gateway (192.168.10.1), and the router ARPs for the NAS (192.168.20.5).

Step 3.4 — The Wireless Path (Radio at Layer 1)

1. Add a Simple PDU from Eng-Tablet to Eng-PC-2.
2. Step it through: Eng-Tablet → (radio) → Eng-AP → Switch-B → Eng-PC-2.
3. At Layer 1 on the first hop, the bits are carried as radio waves; at the AP they are re-encoded onto copper. Note how the wireless 802.11 frame format at Layer 2 is converted to a wired 802.3 Ethernet frame by the access point.

Step 3.5 — The Coax Medium (Layer 1 Observation)

Hover over or inspect the Cable-Modem → Internet-ISP link. At Layer 1 the signal is a modulated radio-frequency wave on a copper coaxial core — the same technology that delivers cable TV. This is a fourth, distinct physical encoding alongside electrical UTP, optical fiber and 802.11 radio.

PDU Field Summary

Focus: switch back to Realtime Mode and confirm everything works with the command-line diagnostic tools a real technician uses.

Click the Realtime tab (bottom-right) to leave Simulation Mode, then open Admin-PC → Desktop tab → Command Prompt.

Step 4.1 — Inspect the Local Configuration

Run ipconfig /all to see the full addressing, including the physical MAC address:

C:\> ipconfig /all

   Physical Address. . . . . . . . . : 0060.5C4B.A9E1
   IPv4 Address. . . . . . . . . . . : 192.168.10.10
   Subnet Mask . . . . . . . . . . . : 255.255.255.0
   Default Gateway . . . . . . . . . : 192.168.10.1

Now run arp -a to view the ARP cache — the table that maps IP addresses to the MAC addresses you watched being resolved in Phase 3:

C:\> arp -a

  Internet Address      Physical Address      Type
  192.168.10.1          00d0.58a2.7c01        dynamic
  192.168.10.50         0002.4a8e.1b3d        dynamic

Step 4.2 — Ping Across the Fiber Backbone

Confirm the 850 m fiber backbone actually carries traffic by pinging Eng-PC-1 in the other building:

C:\> ping 192.168.10.50

Pinging 192.168.10.50 with 32 bytes of data:
Reply from 192.168.10.50: bytes=32 time<1ms TTL=128
Reply from 192.168.10.50: bytes=32 time<1ms TTL=128
Reply from 192.168.10.50: bytes=32 time<1ms TTL=128

    Packets: Sent = 4, Received = 4, Lost = 0 (0% loss)

Step 4.3 — Trace the Route & Compare Hop Counts

Run tracert to both destinations and compare. The switched, same-subnet path shows no router hops:

C:\> tracert 192.168.10.50

Tracing route to 192.168.10.50 over a maximum of 30 hops:

  1    0 ms    0 ms    0 ms    192.168.10.50

Trace complete.

The routed path to the Server Farm crosses the gateway, so it shows one extra hop and measurable latency:

C:\> tracert 192.168.20.5

Tracing route to 192.168.20.5 over a maximum of 30 hops:

  1    0 ms    0 ms    0 ms    192.168.10.1
  2    1 ms    0 ms    1 ms    192.168.20.5

Trace complete.

Step 4.4 — Cable & Media Reference Guide

Step 4.5 — Submission Checklist

• Two-building topology built with all devices labelled exactly as specified.
• Static IP addressing applied across both the 10.0 campus and 20.0 Server Farm subnets.
• Copper links use the correct straight-through / crossover cable, and the Tablet shows a wireless association.
• PT-SWITCH-NM-1FGE modules installed in both switches (power cycled correctly).
• 850 m fiber backbone connected and both fiber interfaces configured via CLI (speed 1000, duplex full, description set).
• PDU screenshots captured showing the Layer 2 MAC rewrite at the router and the constant Layer 3 IPs.
• ipconfig /all, arp -a, ping and tracert outputs saved for both the switched and routed paths.

1. Why is copper UTP limited to 100 metres, and what property of fiber optic cable lets it span the 850 metres between the two buildings?
2. In the PDU Information window, why did the Layer 3 IP addresses stay the same end-to-end while the Layer 2 MAC addresses were rewritten on the routed path but not on the switched path?
3. Describe how the same bits are physically encoded differently across the four media you inspected: UTP copper, fiber optic, coaxial and 802.11 wireless.
4. Why must you power off a Switch-PT switch before inserting the PT-SWITCH-NM-1FGE module?
5. Which Cisco IOS commands set a fiber interface to 1 Gbps full-duplex, and why is manual configuration sometimes needed on optical links?
6. Your tracert to Eng-PC-1 showed zero router hops but the one to Corporate-NAS showed one. Explain what this tells you about where the fiber backbone sits in the OSI model.