Home > Articles > Cisco Certification > CCNA Routing and Switching > 31 Days Before Your CCNA Exam: Connecting Switches and Ethernet Technology

31 Days Before Your CCNA Exam: Connecting Switches and Ethernet Technology

Chapter Description

Allan Johnson provides late study tips and resources for Ethernet and switching topics on the CCNA 640-802 exam.

Benefits of Using Switches

A collision domain is a set of devices whose frames could collide. All devices on a 10BASE2, 10BASE5, or any network using a hub risk collisions between the frames that they send, so all devices on one of these types of Ethernet networks are in the same collision domain and use CSMA/CD to detect and resolve collisions.

LAN switches significantly reduce, or even eliminate, the number of collisions on a LAN. Unlike hubs, switches do not create a single shared bus. Instead, switches do the following:

  • Switches interpret the bits in the received frame so that they can typically send the frame out the one required port, rather than all other ports.
  • If a switch needs to forward multiple frames out the same port, the switch buffers the frames in memory, sending one at a time, thereby avoiding collisions.

In addition, switches with only one device cabled to each port of the switch allow the use of full-duplex operation. Full-duplex means that the NIC can send and receive concurrently, effectively doubling the bandwidth of a 100 Mbps link to 200 Mbps—100 Mbps for sending and 100 Mbps for receiving.

These seemingly simple switch features provide significant performance improvements as compared with using hubs. In particular:

  • If only one device is cabled to each port of a switch, no collisions can occur.
  • Devices connected to one switch port do not share their bandwidth with devices connected to another switch port. Each has its own separate bandwidth, meaning that a switch with 100 Mbps ports has 100 Mbps of bandwidth per port.
8. Ethernet Addressing | Next Section Previous Section