Infrastructure · Topic 3 of 5
Ports on Network Devices
Identify the console, serial, fiber, Ethernet, SFP, USB and PoE ports on Cisco switches and routers, and learn what each port is used for in a network.
- 4 min
- The console port is for local setup and does not carry user traffic. The usual settings are 9600, 8, none and 1.
- A serial port connects a router to a WAN link.
- Ethernet ports are named FastEthernet, GigabitEthernet and TenGigabitEthernet by speed.
What it is
A port is a socket on a device where you attach a cable or a module.
Switches and routers have several kinds of port, and each has its own job. Some carry user traffic, and some are only for managing the device.
You need to look at a port, name it, and know which cable goes in it.
How it works
Management ports are used to set up the device, and data ports carry the traffic.
Console port
The console port is the port you use to set up a device for the first time, or to reach it when the network is down. It does not carry user traffic.
On many Cisco devices it is an RJ-45 socket, connected to a PC with a console cable and a serial or USB adapter. Some devices also have a USB console port.
You then run a terminal program on the PC. The usual starting settings on Cisco devices are 9600 baud, 8 data bits, no parity and 1 stop bit.
Some routers also have an auxiliary port, labelled AUX, which was once used for a dial up modem.
Serial port
A serial port connects a router to a WAN link, such as a leased line, using a serial cable. It is found on older routers and on modules. Do not confuse it with the console port, which is also a serial style connection.
Ethernet ports
Ethernet ports use RJ-45 sockets and twisted pair cable. They are named by speed.
| Name | Speed |
|---|---|
| FastEthernet | 100 Mbps |
| GigabitEthernet | 1 Gbps |
| TenGigabitEthernet | 10 Gbps |
A port might be shown as GigabitEthernet0/1, often shortened to Gi0/1. The numbers give the position of the port.
Some devices have a separate management Ethernet port. It is used for remote management and is kept apart from user traffic.
Fiber ports and SFPs
Many devices have empty slots for SFP modules, which stands for small form factor pluggable. An SFP is a small module that you push into the slot, and the cable then plugs into the module.
The module decides the type of link. One SFP might take a fiber cable, and another might take copper.
This means that one switch can have different uplinks without changing the hardware. An SFP+ module is the 10 Gbps version.
Fiber ports are often used for uplinks between switches, because fiber reaches further than copper.
USB port
A USB port can be used to read or write files on a USB flash drive. It can hold software images or configuration files. On some devices it can also be the console port.
PoE ports
A PoE port supplies electrical power over the Ethernet cable as well as data. It lets a switch power a phone, camera or access point without a separate power supply.
| Standard | Common name | Power per port at the switch |
|---|---|---|
| IEEE 802.3af | PoE | 15.4 W |
| IEEE 802.3at | PoE+ | 30 W |
| IEEE 802.3bt | PoE++ | Up to 60 W or 90 W, depending on the type |
What to remember for the exam
Seven facts cover most questions on this topic.
- The console port is for local setup and does not carry user traffic. The usual settings are 9600, 8, none and 1.
- A serial port connects a router to a WAN link.
- Ethernet ports are named FastEthernet, GigabitEthernet and TenGigabitEthernet by speed.
- An SFP is a pluggable module that adds a fiber or copper port. SFP+ runs at 10 Gbps.
- A USB port can read files from a flash drive and on some devices acts as a console.
- PoE delivers power and data over one Ethernet cable.
- PoE is 15.4 W, PoE+ is 30 W, and PoE++ goes up to 60 W or 90 W, depending on the type.
If the question mentions setting up a new device with no network access, the answer is the console port.
Common mistakes
These four errors appear again and again.
Plugging a network cable into the console port. The console port looks like an Ethernet port but is not one. Look for the label.
Using the wrong module in an SFP slot. The module must suit the cable you plan to use.
Assuming all ports give PoE. Only the ports on a PoE capable switch do, and the switch has a limited power budget.
Confusing serial and console. Serial links a router to a WAN. Console is for management.
Fiber ports can emit invisible light. Do not look into the end of a fiber cable or port.
Check yourself
Work through these three questions.
Which port do you use to configure a new switch directly from a laptop?
Use the console port.
What is an SFP?
An SFP is a small pluggable module that fits a slot and provides a fiber or copper port.
What does PoE do?
It supplies power to a device over the Ethernet cable that also carries its data.
Topic 3 of 5 in Infrastructure
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