4.2 VLAN Types
4.2.2 End-to-end VLANs
VLANs can exist either as end-to-end networks, which span the entire switch fabric, or they can exist inside of geographic boundaries.

An end-to-end VLAN network comprises the following characteristics:

  • Users are grouped into VLANs independent of physical location and dependent on group or job function.
  • All users in a VLAN should have the same 80/20 traffic flow patterns.
  • As a user moves around the campus, VLAN membership for that user should not change.
  • Each VLAN has a common set of security requirements for all members.

In the Figure, starting in the wiring closet, 10-megabit-per-second (Mbps) dedicated Ethernet ports are provisioned for each user. Each color represents a subnet and, because people have moved around over time, each switch eventually becomes a member of all VLANs. Fast Ethernet Inter-Switch Link (ISL) or IEEE 802.1Q is used to carry multiple VLAN information between the wiring closets and the distribution-layer switches. 

Note: ISL is a Cisco-proprietary protocol that maintains VLAN information as traffic flows between switches and routers. IEEE 802.1Q is an open-standard (IEEE) VLAN tagging mechanism that predominates in modern switching installations.

Workgroup servers operate in a client/server model, and attempts have been made to keep users in the same VLAN as their server to maximize the performance of Layer 2 switching and keep traffic localized.

In the core, a router allows inter-subnet communication. The network is engineered, based on traffic flow patterns, to have 80 percent of the traffic within a VLAN and 20 percent crossing the router to the enterprise servers and to the Internet and WAN.