Infrastructure · Topic 2 of 5
Cabling Devices from a Network Diagram
Learn to read a simple network diagram and pick patch, console and power cables for switches and routers, including straight through and crossover.
- 4 min
- Use a straight through cable to join unlike devices, such as a PC to a switch.
- Use a crossover cable to join like devices on older ports. Modern ports often detect this automatically.
- Use a console cable to configure a device from a PC.
What it is
A network diagram is a drawing that shows which devices exist and how they connect.
An engineer may give you a diagram and ask you to attach the cables. You need to read the symbols, choose the right cable for each link, and put the equipment in a tidy rack.
Good cabling is neat, labelled and matches the drawing exactly.
How it works
Match each line on the diagram to a cable type, then connect, power and label everything.
Reading the diagram
A diagram uses symbols for routers, switches and endpoints. A line between two symbols is a link, and labels beside the line often give the port names, such as Gi0/1.
Follow the labels exactly. If the diagram says the PC connects to port Gi0/3, plug it into that port, not the one next to it.
Choosing patch cables
A patch cable is a short twisted pair cable with an RJ-45 connector at each end. The type you choose depends on the devices you join.
| Link | Cable |
|---|---|
| PC to switch | Straight through |
| Router to switch | Straight through |
| Switch to switch | Crossover on older ports |
| Router to PC | Crossover on older ports |
| Router to router | Crossover on older ports |
A straight through cable has the same wire order at both ends, and joins unlike devices. A crossover cable swaps the transmit and receive pairs, and joins like devices.
Most modern Cisco switch ports detect the type of cable on their own, so a straight through cable usually works. This feature is called Auto-MDIX.
Other cables you may be asked for are:
- A console cable from a PC to the console port, for setting up a device.
- A fiber patch cable between SFP ports.
- A serial cable for older WAN links.
Small topologies
A small office often has one router, one or two switches and a few PCs. The router connects to the provider, the switch connects to the router, and the PCs connect to the switch.
Connect the uplink between the switch and the router first. Then connect the endpoints one at a time, and check that each port light turns green.
Power
Plug each device into a power outlet or a power strip. In a rack, a PDU (power distribution unit) provides the sockets. A UPS (uninterruptible power supply) keeps equipment running briefly during a power cut.
Some switches also feed power to devices over the cable, using PoE. A device with a spare power supply can be connected to two power sources.
Rack layout
Most network equipment is mounted in a standard 19 inch rack. Height is measured in rack units, written U, where 1U is 44.45 mm, or 1.75 inches.
Good layout follows a few habits:
- Place heavy equipment, such as a UPS, near the bottom.
- Put a patch panel near the switches, so cables from the wall run to the panel and short patch cables run on to the switch.
- Leave airflow gaps and use cable management bars.
- Label both ends of each cable and each port.
Tidy cabling makes faults easier to find. A label saves a long search later.
What to remember for the exam
Six facts cover most questions on this topic.
- Use a straight through cable to join unlike devices, such as a PC to a switch.
- Use a crossover cable to join like devices on older ports. Modern ports often detect this automatically.
- Use a console cable to configure a device from a PC.
- A rack unit, 1U, is 1.75 inches high, and the standard rack is 19 inches wide.
- A patch panel links wall cabling to the switches with short patch cables.
- Follow the diagram's port labels, and label the cables you fit.
When the diagram shows two different kinds of device, a straight through cable is nearly always the right answer.
Common mistakes
These four errors appear again and again.
Plugging into the wrong port. The diagram names the port, so follow it exactly.
Using a crossover cable where a straight through is needed. The link may not come up, unless the port detects the cable.
Putting heavy gear at the top of the rack. It makes the rack unstable.
Forgetting labels. An unlabelled cable can take a long time to trace.
Do not move a cable on a live network without asking the engineer first. Unplugging the wrong cable can cut users off.
Check yourself
Work through these three questions.
Which cable joins a PC to a switch?
A straight through cable joins them.
What is a patch panel used for?
It links the permanent wall cabling to the switches, using short patch cables.
How high is one rack unit?
One rack unit, 1U, is 1.75 inches, or 44.45 mm.
Topic 2 of 5 in Infrastructure
Test yourself on Infrastructure
The full Cisco CCST 100-150 Networking question bank has 749 questions, with timed practice exams and an explanation for every answer.
This study guide is independent and is not affiliated with, endorsed by, or sponsored by Cisco. Vendor names, certification names and exam codes are trademarks of their respective owners and are used for identification only.