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Switch Interfaces

This page provides introduction to Switch Interfaces.

Overview​

Switches are used to forward traffic within a Local Area Network (LAN). By default, switch interfaces are active and do not have the shutdown command applied, whereas router interfaces are shut down by default. It's important to disable unused interfaces as they can pose a security risk.

Duplex Modes​

There are two types of duplex modes:

  • Half Duplex: Devices cannot send and receive data simultaneously. Devices connected to hubs operate in half-duplex mode, which is now outdated.
  • Full Duplex: Devices can send and receive data simultaneously.

CSMA/CD​

  • CSMA/CD stands for carrier sense multiple access with collision detection.
  • A device listens to the collision domain before sending a frame to ensure that no other devices are transmitting.
  • If collision does occurs, the device sends a jamming signal to inform the other devices that a collision happened.
  • Each device will then wait for a random period of time before sending frames again.
  • The process repeats.
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CSMA/CD is an outdated collision detection mechanism used only in hubs, which operate in half-duplex mode.

Autonegotiation​

  • Interfaces that can run at different speeds(10/10010/100 or 10/100/100010/100/1000) have default settings of speed auto and duplex auto.
  • Interfaces advertise their capabilities to the neighbouring device, and they negotiate the best speed and duplex settings they are both capable of.
  • All the devices connected to switch should be using Autonegotiation for the best performance.
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  • E - Stands for ethernet interface and runs at 1010 Gbits/second
  • F - Stands for fast ethernet interface and runs at 10/10010/100 Gbits/second
  • G - Stands for Gigabit ethernet interface and runs at 10/100/100010/100/1000 Gbits/seconds

Interface Error Output​

Below are some of the counters from interface error output.

  • Runts: Frames that are smaller than minimum ethernet frame size(6464 bytes) of an interface.
  • Giants: Frames that are larger than maximum ethernet frame size(15181518 bytes) of an interface.
  • CRC: Frames that failed the CRC check (Cyclic Redundancy Check).
  • Frame: Frames that have incorrect format.