VLAN & Configuration Quiz

VLAN Concept and Introduction

• A Virtual Local Area Network (VLAN) is a broadcast domain that is partitioned and isolated in a computer network at the data link layer (OSI layer 2)
• VLANs work by applying tags to network frames and handling these tags in networking systems, creating the appearance and functionality of network traffic that is physically on a single network but acts as if it is split between separate networks
• VLANs can keep network applications separate despite being connected to the same physical network, without requiring multiple sets of cabling and networking devices to be deployed

VLAN Implementation

• To subdivide a network into VLANs, one configures network equipment
• Simpler equipment might partition only each physical port, while more sophisticated devices can mark frames through VLAN tagging, allowing a single interconnect (trunk) to transport data for multiple VLANs
• VLANs can be used to partition a local network into several distinctive segments, such as production, voice over IP, network management, storage area network (SAN), guest internet access, and demilitarized zone (DMZ)
• A common infrastructure shared across VLAN trunks can provide a measure of security with great flexibility for a comparatively low cost

VLANs Benefits

• VLANs address issues such as scalability, security, and network management
• VLANs provide the flexibility to adapt to changes in network requirements and allow for simplified administration
• VLANs can keep network applications separate despite being connected to the same physical network
• VLANs can optimize traffic on trunk links for real-time or low-latency requirements

VLAN History

• Dr. W. David Sincoskie invented VLANs by adding a tag to each Ethernet frame, allowing for improved scalability and bandwidth
• Sincoskie referred to this as a multitree bridge
• The concept of VLANs was first introduced in the 1980s, and the IEEE 802.1Q standard was published in 1998

VLAN Trunks

• A trunk denotes a network link carrying multiple VLANs, which are identified by labels (or tags) inserted into their packets
• Such trunks must run between tagged ports of VLAN-aware devices, often switch-to-switch or switch-to-router links rather than links to hosts
• VLAN port assignment charts or diagrams are necessary to indicate VLAN to port associations

VLAN Protocols and Design

• The protocol most commonly used today to support VLANs is IEEE 802.1Q
• Prior to the introduction of the 802.1Q standard, several proprietary protocols existed, such as Cisco Inter-Switch Link (ISL) and 3Com's Virtual LAN Trunk (VLT)
• VLAN cross connect (CC or VLAN-XC) is a mechanism used to create Switched VLANs, using IEEE 802.1ad frames where the S Tag is used as a Label as in MPLS

VLAN Configuration

• To configure a VLAN, one must login to the switch with console and type the commands to create a VLAN, name it, and assign it to ports
• The commands include switch#configure terminal, switch(config)#vlan 2, switch(config-vlan)#name CSC, switch(config-vlan)#exit, and switch(config)#interface fastEthernet 0/14 for a single port, or switch(config)#int range fastEthernet 0/15-16 for multiple ports
• The show vlan brief command is used to verify VLANs and their associated ports