Switch Interface duplex | speed | Auto-Negotiation explained | Free CCNA 200-301 course
Notes
Cisco IOS uses the term interface to refer to physical ports on a network device used to forward data to and from other devices.
Each interface can be configured with several settings, each of which might differ from interface to interface.
IOS uses interface subcommands to configure these settings.
Let us begin with a discussion of three relatively basic per-interface settings:
the port speed, duplex, and a text description.
1. Speed:
Speed is the rate of the interface, usually listed in megabits per second (Mbps).
Common Ethernet speeds include 10 Mbps, 100 Mbps, and 1,000 Mbps. 2. Duplex
Duplex refers to how data flows on the interface.
On a half-duplex interface, data can only be transmitted or received at any given time.
A full-duplex interface, on the other hand, can send and receive data simultaneously.
3.Description
The description text interface subcommand lets you add a text description to the interface.
It is meant to provide a reminder in the configuration to describe what certain interfaces are used for.
It is a text description configured by the administrator.
The show interfaces status command lists much of the detail configured even with only one line of output per interface.
Configuring Multiple Interfaces with the interface range Command
to shorten your configuration work when making the same setting on multiple consecutive interfaces.
To do so, use the interface range command.
For example for interfaces from 11 till 20 end users will be connected.
Administratively Controlling Interface State with shutdown
As you might imagine, network engineers need a way to bring down an interface without having to travel to the switch and remove a cable.
In short, we need to be able to decide which ports should be enabled and which should be disabled.
Cisco uses two interface subcommands to configure the idea of administratively enabling and disabling an interface:
the shutdown command (to disable) and the no shutdown command (to enable). .
In this case, switch SW1 has a working interface F0/1.
Removing Configuration with the no Command
you can revert to the default setting by issuing a no version of the command.
switch SW1’s F0/2 port has been configuredwith speed 100, duplex half, description link to 2901-2, and shutdown.
Let me give you an example
the no speed command on that same interface reverts to the default speed setting (which happens to be speed auto). -Same idea with the duplex command: an earlier configuration of duplex half followed by no duplex on the same interface, reverts the configuration back to the default of duplex auto. -use the no description command. to go back to the default state of having no description on that interface,
WHAT IS ETHERNET AUTO-NEGOTIATION?
Auto-negotiation is the feature that allows a port on a switch, router, server, or other device to communicate with the device on the other end of the link to determine the optimal duplex mode and speed for the connection.
For any 10/100 or 10/100/1000 interfaces Cisco Catalyst switches default to a setting of duplex auto and speed auto.
As a result, those interfaces attempt to automatically determine the speed and duplex setting to use.
Alternatively, you can configure most devices, switch interfaces included, to use a specific speed and/or duplex.
Ethernet devices on the ends of a link must use the same standard; otherwise, they cannot correctly send data.
For example, a NIC cannot use 100BASE-T, which uses a UTP cable with a 100-Mbps speed, while the switch port on the other end of the link uses 1000BASE-T.
the link would not work with one end trying to send at 100 Mbps while the other tried to receive the data at 1000 Mbps.
The IEEE auto-negotiation (802.3u)protocol helps makes it much easier to operate a LAN when NICs and switch ports support multiple speeds.
IEEE auto-negotiation defines a protocol that lets the two UTP-based Ethernet nodes on a link negotiate so that they each choose to use the same speed and duplex settings.
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