Specifications

Configuring Routing Between VLANs

Information About Routing Between VLANs

This module describes routing between VLANs. It contains the following sections:

• Virtual Local Area Network Definition, page 2

• VLAN Performance, page 4

• VLAN Colors, page 8

• Implementing VLANS, page 9

• Communication Between VLANs, page 9

• VLAN Interoperability, page 11

• Designing Switched VLANs, page 12

Virtual Local Area Network Definition

A virtual local area network (VLAN) is a switched network that is logically segmented on an

organizational basis, by functions, project teams, or applications rather than on a physical or

geographical basis. For example, all workstations and servers used by a particular workgroup team can

be connected to the same VLAN, regardless of their physical connections to the network or the fact that

they might be intermingled with other teams. Reconfiguration of the network can be done through

software rather than by physically unplugging and moving devices or wires.

A VLAN can be thought of as a broadcast domain that exists within a defined set of switches. A VLAN

consists of a number of end systems, either hosts or network equipment (such as bridges and routers),

connected by a single bridging domain. The bridging domain is supported on various pieces of network

equipment; for example, LAN switches that operate bridging protocols between them with a separate

bridge group for each VLAN.

VLANs are created to provide the segmentation services traditionally provided by routers in LAN

configurations. VLANs address scalability, security, and network management. Routers in VLAN

topologies provide broadcast filtering, security, address summarization, and traffic flow management.

None of the switches within the defined group will bridge any frames, not even broadcast frames,

between two VLANs. Several key issues described in the following sections need to be considered when

designing and building switched LAN internetworks:

• LAN Segmentation, page 3

• Security, page 3

• Broadcast Control, page 4

• VLAN Performance, page 4

• Network Management, page 4

• Network Monitoring Using SNMP, page 4

• Communication Between VLANs

• Relaying Function, page 4

• Native VLAN, page 6

• PVST+, page 7

• Ingress and Egress Rules, page 8

• Integrated Routing and Bridging, page 8