Chabot College

ET 99.09 Cisco Semester 3 Chapter 3 VLANs M. McGregor, Los Medanos College, Pittsburg, CA Chabot College

Introduction to VLANs Chabot College

What is a VLAN?

Chabot College

Why create VLANs?

Chabot College

Switches are the core of VLANs Chabot College

VLAN Switching and Filtering

Each switch has the intelligence to make filtering and forwarding decisions by

frame

, based on VLAN metrics defined by network managers, and to communicate this information to other

switches

and

routers

within the network.

Chabot College

Frame filtering and tagging

The most common approaches for logically grouping users into distinct VLANs are: •

frame filtering

•

frame tagging

Chabot College

Frame Filtering Chabot College

Tradeoffs with frame filtering

•

Filter-based

VLANs do not scale well because each frame has to be referenced to a lookup table.

• The IEEE 802 committee has adopted

frame tagging

as the standard because it is more scalable.

Chabot College

IEEE 802 VLAN Standardization Chabot College

Frame Tagging Chabot College

VLAN Flexibility Chabot College

Problems with broadcasts Chabot College

Problems with broadcasts

When no routers are placed between switches, broadcasts (Layer 2 transmissions) are sent to every switched port. This is commonly referred to as a

“flat” network

where there is one broadcast domain across the entire network

Chabot College

VLANs can control broadcasts Chabot College

VLANs can provide security Chabot College

VLANs provide flexibility Chabot College

Where are the routers?

Layer 3 communication

, either embedded in the switch or provided externally, is an integral part of any high-performance switching architecture.

Chabot College

What are hubs good for?

Chabot College

Leveraging your investment Chabot College

Port-Centric VLANs Chabot College

Port-centric VLANs

VLAN Membership by port maximizes forwarding performance because:  Users are assigned by port .  VLANs are easily administered  Maximizes security between VLANs  Packets do not “leak” into other domains  VLANs and membership are easily controlled across network

Chabot College

Static VLANs Chabot College

Dynamic VLANs

Dynamic VLANs are ports on a switch that can automatically determine their VLAN assignments.

Chabot College

VLANs across backbones Chabot College

VLANs across backbones

• • •

Fast Ethernet - ISL (Inter-Switch Link) FDDI - IEEE 802.10

ATM - LAN Emulation (LANE) Chabot College

VTP - VLAN Trunk Protocol

• • • • • • • •

VTP Domain VTP Configuration revision number VLAN IDs (ISL) Emulated LAN names (ATM) 802.10 SAID values (FDDI) MTU Frame format VLAN configuration Chabot College