Junos® OS For Dummies®, 2nd Edition

Ethernet, VLANs, and Juniper EX-Series Switches

Ethernet is the most common LAN technology today, so to understand virtual LANs (VLANs) switches, you need to understand Ethernet. VLANs, made up of pieces of what would ordinarily be massive, unwieldy collections of networked devices, make Ethernets more tractable for the modern world.

Finally, because the collection of VLANs and Ethernets must all still work and feel as one to users and managers, we'll look at how switches tie it all back together.

Understanding Ethernet

Over the years, Ethernet, which is technically IEEE 802.3 CSMA/CD LANs (although no one uses that terminology), has become the most commonly used standard for enterprise networks. These networks carry voice, graphics, and video traffic over interfaces that run considerably faster than the original Ethernet. The most common top speed, for example, is a full thousand times faster than the original Ethernet — 10 gigabits per second (Gbps) versus 10 megabits per second (Mbps).

With so much data being carried, the potential increases for more and more packet collisions in the collision domain. When a collision occurs, both data frames must be resent and this cuts down drastically on the throughput of the LAN. The collision domain is established by the number of hosts that can be transmitting at the same time and cause a collision. If you can have two hosts blasting away at the same time, you have at least two collision domains on the LAN.

The IEEE addressed this issue ...