Creating Virtual Local Area Networks (VLANs)
Understanding the creation and management of VLAN’s in today’s modern networks is crucial to a successful network engineer. This lab will discuss and demonstrate the configuration and verification of VLAN’s on the Catalyst Series Switch.
Real World Application & Core Knowledge
First off lets start off with the definition of a flat network. A Flat network is a type of network design where the network engineer unknowingly daisy chains together hubs and/or switches to create one single large network that encompass hundreds if not thousands of devices in a broadcast domain.
From a design perspective this is an insanely bad idea as broadcast and control traffic can overwhelm the network. In a real world production multi-access network such as ethernet you will notice network performance degrades when you hit the 400+ host on a given subnet. The most common network size is a /24 netmask which can address 254 usable host ip addresses.
So how do you create a network larger then 400+ nodes? The answer is actually quite a simple 4 letter acronym called VLAN’s. Virtual Local Area Networks in the simplest terms partitions a physical switch into multiple isolated LAN’s so that traffic on one VLAN cannot communicate to traffic on another VLAN unless it is done so by a router. VLAN’s can easily be explained as layer 2 network segregation, whereas layer 3 segregation would be considered sub netting which will be discussed in section 6.
The driving factor to create VLAN’s is to control the size of a given layer 2 network segment so that broadcast and control traffic does not overwhelm the given network segment.
Keep in mind when working with the Free CCNA Workbook GNS3 topology that SW1, SW2 and SW3 are Cisco 3640 series routers with the NM-16ESW switch module. This switch module is configured differently then Cisco Catalyst Series switches. To configure VLAN’s on a router which has the NM-16ESW module installed you’ll need to create the VLAN’s in VLAN Database Configuration mode. Keep in mind that the VLAN Database configuration mode has been depreciated in newer Cisco switch IOS software and creating a VLAN on a Cisco switch is now done via global configuration mode using the vlan # name VLAN_NAME command.
Also note that when verifying NM-16ESW switch configurations that the commands will be slightly different then a Cisco Catalyst Switch running IOS. It is recommended to purchase a Cisco Catalyst switch such as a 2950G or preferably a 3550 to familiarize yourself with the commands on a Catalyst based switch.
In this lab you will familiarize yourself with the following commands;
| Command | Description |
|---|---|
| vlan database | This command is executed in privileged mode which places you into VLAN Database configuration mode. If you are using the Free CCNA Workbook GNS3 topology then this command will be used quite often throughout Section 4 as SW1, SW2 and SW3 are Cisco 3640′s with the NM-16ESW Switch module installed in slot0. |
| vlan # name vlan_name | This command is executed in VLAN Database configuration mode to create and name a VLAN when using the NM-16ESW. |
| abort | This command is executed in VLAN Database configuration mode to exit the VLAN Database configuration mode without applying any changes that you made while in VLAN Database configuration mode. |
| apply | This command is executed in VLAN Database configuration mode will apply any current VLAN Database configuration changes you’ve made during your session. |
| exit | This command is executed in VLAN Database configuration mode and will apply changes that you’ve made while in VLAN Configuration mode and exit back to privileged mode. |
| no vlan # | This command can be executed in VLAN Database configuration mode or VLAN configuration mode to remove the VLAN that you specify. i.e; no vlan 20 |
| reset | This command is executed in VLAN Database configuration mode will abandon any current changes made while in VLAN Configuration mode and reread the current VLAN Database. |
| vlan # | Executed from Global Configuration mode and creates a new VLAN with the specified VLAN number, once the VLAN is created you will be placed into vlan configuration mode. |
| vlan VLAN_NAME | This command is executed in VLAN Configuration mode to assign a name to the specified VLAN number. (Note, Not VLAN Database Configuration Mode) |
| switchport access vlan # | This command is executed in interface configuration mode to assign a switchport to a specified VLAN. |
| show vlan | This command can be executed from user or privileged mode on a Catalyst Switch (Cisco Catalyst 2950, 3500, 3560, 3750 etc…) to view the current vlan configuration. |
| show vlan-switch | This command can be executed in user or privileged mode on a Cisco router that has a Switch WIC, HWIC, or Network Module such as the NM-16ESW which is included on SW1, SW2 and SW3 in the Free CCNA Workbook GNS3 topology. |
Lab Prerequisites
- If you are using GNS3 than load the Free CCNA Workbook GNS3 topology than start devices; SW1.
- Establish a console session with devices SW1 than configure the devices respected hostname(s).
Lab Objectives
- On SW1, create 3 VLAN’s. VLAN 10 with the name Sales, VLAN 20 with the name Development, VLAN 30 with the name Marketing.
- Assign Port Fa0/1 to VLAN 10, assign interface Fa0/2 to VLAN 20 and assign interface Fa0/3 to VLAN 30. Afterward, verify your configuration.
Lab Instruction
Step 1. – On SW1, create 3 VLAN’s. VLAN 10 with the name Sales, VLAN 20 with the name Development, VLAN 30 with the name Marketing.
To complete this objective using GNS3 you will need to navigate to VLAN Database configuration mode by using the vlan database command in privileged mode. Once in VLAN Database configuration mode you can create the VLAN’s by using the vlan number name vlan_name command.
SW1 con0 is now available Press RETURN to get started. SW1>enable SW1#config terminal Enter configuration commands, one per line. End with CNTL/Z. SW1(config)#vlan 10 SW1(config-vlan)#name Sales SW1(config-vlan)#vlan 20 SW1(config-vlan)#name Development SW1(config-vlan)#vlan 30 SW1(config-vlan)#name Marketing SW1(config-vlan)#end SW1#
Step 2. – Assign Port Fa0/1 to VLAN 10, assign interface Fa0/2 to VLAN 20 and assign interface Fa0/3 to VLAN 30. Afterward, verify your configuration.
To configure switchport interfaces in a specific vlan you will use the switchport access vlan # command in interface configuration mode. To verify your vlan configuration you’ll use the show vlan-switch when configuring the NM16-ESW or show vlan on a Cisco Catalyst Series switch in user or privileged mode as shown below on a Catalyst Series switch.
SW1#configure terminal SW1(config)#interface Fa0/1 SW1(config-if)#switchport access vlan 10 SW1(config-if)#interface Fa0/2 SW1(config-if)#switchport access vlan 20 SW1(config-if)#interface Fa0/3 SW1(config-if)#switchport access vlan 30 SW1(config-if)#end SW#show vlan VLAN Name Status Ports ---- ---------------------------- --------- ------------------------------- 1 default active Fa0/4, Fa0/5, Fa0/6, Fa0/7 Fa0/8, Fa0/9, Fa0/10, Fa0/11 Fa0/12, Fa0/16, Fa0/17, Fa0/18 Fa0/19, Fa0/20, Fa0/21, Fa0/22 Fa0/23, Fa0/24, Gi0/1, Gi0/2 10 Sales active Fa0/1 20 Development active Fa0/2 30 Marketing active Fa0/3 1002 fddi-default act/unsup 1003 token-ring-default act/unsup 1004 fddinet-default act/unsup 1005 trnet-default act/unsup SW1#
