VLANs (Virtual Local Area Networks) serve several purposes in a network. Two primary purposes are:
* Segmentation of the Network: VLANs logically segment a network into different broadcast domains, which helps in managing and controlling broadcast traffic. This segmentation helps improve performance and security by isolating certain types of traffic from others.
* Creating Broadcast Domains: Each VLAN is a separate broadcast domain. By using VLANs, a network administrator can reduce the size of broadcast domains, thereby reducing broadcast traffic and increasing the efficiency of the network.
These purposes are in line with Cisco's network design principles and best practices for using VLANs.
References: Cisco DevNet Associate Certification Guide, Chapter on VLANs and their uses.