# 7 Configuring and Verifying Switch Interfaces
###### tags: `CCNA`
### Configuring Switch Interfaces

#### Configuring Speed, Duplex, and Description
:::info
SW的Interface 支援很多速度
10/100
10/100/1000
duplex auto full half
speed auto 10 100 1000
:::

### Configuring Multiple Interfaces with the interface range Command

### 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.
### Removing Configuration with the no Command

**Autonegotiation**
For any 10/100 or 10/100/1000 interfaces—that is, interfaces that can run at different
speeds—Cisco Catalyst switches **default to a setting of ==duplex auto== and ==speed auto==.**

**The protocol messages flow outside the normal Ethernet electrical frequencies as out-of-band signals over the UTP cable.**
Basically, each node states what it can do, and then each node picks the best options that both nodes support: the fastest speed and the best duplex setting, with full duplex being better than half duplex.

IEEE autonegotiation defines some rules (defaults) that nodes should use as defaults ==when autonegotiation fails—that== is, when a node tries to use autonegotiation but hears nothing from the device.
The rules:
- Speed: Use your slowest supported speed (often 10 Mbps).
- Duplex: If your speed = 10 or 100, use half duplex; otherwise, use full duplex.

==Ethernet interfaces using speeds faster than 1 Gbps always use full duplex.==


**Autonegotiation and LAN Hubs**

### Interface Status Codes and Reasons for Nonworking States

### Interface Speed and Duplex Issues

For example, consider ports Fa0/12 and Fa0/13 in the output of the show interfaces status command.

For **Fa0/13, a-full means full duplex as autonegotiated**, whereas half on Fa0/12 means half duplex but as manually configured. The example shades the command output that implies that the switch’s **Fa0/12 interface’s speed and duplex were not found through autonegotiation**, but Fa0/13 did use autonegotiation.


### Common Layer 1 Problems on Working Interfaces