VLAN (Virtual LAN) Configurations

VLAN provides Virtual Segmentation of Broadcast Domain in the network. The devices, which are member of same Vlan, are able to communicate with each other. The devices of different Vlan may communicate with each other with routing. So that different Vlan devices will use different n/w addresses. Vlan provides following advantages: -

(1) Logical Segmentation of network

(2) Enhance network security 

Creating port based Vlan

In port based Vlan, first we have to create a Vlan on manageable switch then we have to add ports to the Vlan.

Commands to create Vlan

Switch#config ter

Switch(config)#vlan <no>

[name <word>]

Switch(config)#exit                optional

                   Or

 Switch#vlan database

Switch(vlan)#vlan <no>

 [name <word>]

Switch(vlan)#exit

Commands to configure ports for a Vlan

By default, all ports are member of single vlan that is Vlan1. we can change vlan membership according to requirement. 

Switch#conf ter

Switch(config)#interface <type> <no>

Switch(config-if)#switchport access vlan <no>

Switch(config-if)#exit

Commands to configure multiple ports in a vlan

Switch#conf ter

Switch(config)#interface range <type> <slot/port no (space)–(space) port no>

Switch(config-if)#switchport access vlan <no>

Switch(config-if)#exit

Example: - Suppose we want to add interface fast Ethernet 0/10 to 0/18 in vlan5

Switch#config ter

Switch(config)#interface range fastethernet 0/10 – 18

Switch(config-if)#switchport access vlan 5

Switchconfig-if#exit

In 1900 & Compatible switches

Switch#config ter

Switch(config)#interface <type> <no>

Switch(config-if)#vlan-membership static <vlan no>

Switch(config-if)#exit

To Disable web access in switch

Switch#config ter

Switch(config)#no ip http server

To display mac address table

Switch#sh mac-address-table

Vlan    Mac address                type                 ports

20        00-08-a16-ab-6a-7b     dynamic          fa0/7

To Display Vlan and port membership

Switch#sh vlan

Trunking

When there are multiple switches then we have to use trunk links to connect one switch with other. If we are not using trunk links then we have to connect one cable from each vlan to the corresponding vlan of the other switch.

Switches will perform trunking with the help of frame tagging. The trunk port will send data frames by adding a Vlan id information to the frame, at the receiving end vlan id information is removing from the end and according to the tag data is delivered to the corresponding vlan. There are two protocols to perform frame tagging.

(1) Inter switch link (cisco prop)

(2) IEEE 802.1 q

Configuring Trunking

 In cisco switches all switch ports may be configured in three modes

(1) Trunk desirable (default)

(2) Trunk on

(3) Trunk off

Switch#conf ter

Switch(config)#interface <type> <no>

Switch(config-if)#switchport mode <trunk|access|auto>

Switch(config-if)#exit     

To configure Vlans allowed on Trunk

By default all Vlans are allowed on Trunk port. We can add/remove a partucular Vlan from trunk port with following command

Switch#config ter

Switch(config)#interface <type> <no>

Switch(config-if)#switchport trunk allowed vlan all

                                                                               Remove <vlan>

                                                                               Add <vlan>

                                                                               Except <vlan>

To display trunk interfaces

Switch#sh interface trunk

Switch#sh interface <type> <no> trunk    

Posted in: CCNA