Topic 5—Isolation and Segmentation
VLANs
A common technique for implementing network security is to segment an organization’s network so that each
segment can be separately controlled, monitored and protected. Virtual local area networks (VLANs) are groups of
devices on one or more logically segmented LAN.
A VLAN is set up by configuring ports on a switch, so devices attached to these ports may communicate as if they
were attached to the same physical network segment, although the devices are actually located on different LAN
segments. Segmenting network traffic in this way enables an organization to keep different types of data separate
from one another.
A VLAN is based on logical rather than physical connections and, thus, it allows great flexibility. This flexibility
enables administrators to segment network resources for optimal performance by restricting users’ access of network
resources to the necessary individuals only. In Layer 4 switching (transport layer), some application information is
taken into account along with Layer 3 addresses. For IP, this information includes the port numbers from protocols
such as UDP and TCP. These devices, unlike Layer 3 switches, are more resource intensive because they have to store
application-based protocol information. Only address information is stored at the Layer 2 and Layer 3 levels.