WHAT IS VLAN ?  VLAN IS A SHORT FORM OF VIRTUAL LAN.  VLAN JUST LIKE TO BREAKING DOWN LARGE 48 PORT SWITCH INTO SMALLER SWITCHES.  LOGICAL WAY OF GROUPING OR SAPRATE THE SWITCH INTO DIFFERENT NETWORKS.  WE CAN MAKE SAPRATE VLANS FOR EVERY DEPARTMENT LIKE SALES, MARKETING, MANAGEMENT, ETC.

FIRST WE KNOW WORKING OF SWITCH  SWITCH HAS MULTIPLE COLISION DOMAIN.  EACH PORT OF SWITCH HAS ITS OWN COLLISION DOMAIN.  SWITCH IS A INTELLEGENT DEVICE, IT FILTERS THE NETWORK BY USING MAC TABLE.  A DEVICE CONNECTED WITH ONE PORT TRY TO COMMUNICATE WITH ANOTHER PORT DEVICE ON SAME SWITCH WITHOUT COLLIDING TRAFFIC, THEY ARE INDEPENDENT WITH EACH OTHER.

SWITCH HAS ONE BROADCAST DOMAIN  ALL 48 PORTS OF SWITCH ARE IN ONE BRAODCAST DOMAIN.  IF MULTIPLE DEVICES CONNECTED AND ONE OF THOSE DEVICE SEND A BROADCAST THE SAME BROADCASET SENT OUT OF ALL ACTIVE PORTS OF SWITCH.  EXAMPLE – IF YOU ARE IN ONE BIG ROOM AND ONE SPEAKS LOUDLY EVERY BODY HEAR IT.

WHY DO WE NEED VLAN ?  ASSUME WE DO NOT CREATE VLAN IN OUR SWITCH, IT MEANS ALL 48 PORTS ARE IN SAME DEFAULT VLAN, AND ONE NEW JOINING COMES IN SALES DEPARTMENT, HE CAN ACCESS ALL IMPORTANT SHARED FOLDERS IN THE NETWORK.  DANGER OF HAVING ONE BIG BRAODCAST DOMAIN IF ONE DEVICE GETS MALFUNCTION AND START SENDING BRAODCAST IT WILL JAM THE WHOLE NETWORK.  ONE MAILFUNCTION CAN GET DOWN THE ENTIRE NETWORK.  ONE DEVICE SEND BROADCAST LOUDLY NO OTHER DEVICE CAN WORK EFFICIENTLY.

DIAGRAM DISCRIPTION  IN THIS CASE I HAVE MARKED THREE PORTS (IN BLUE COLOR) ARE IN VLAN 10 AND (RED PORTS) IN VLAN 20.  ANY COMMUNICATION OR ANY BROADCAST IS COMING FROM BLUE PORT IS ONLY GO OUT OTHER BLUE PORTS, IT WILL NOT REACH ANY OF THOSE OTHER PORTS.  ASSUME IN YOUR OFFICE ONE PART OF MANAGEMENT STAF IS SITTING IN BUILDING ONE AND ANOTHER PART OF MANAGEMENT STAFF IS SITTING IN BULDING TWO AND YOU WANT TO ADD THEM IN SAME VLAN OR NETWORK IT WILL ONLY POSSIBLE THROUGH CREATING SAME VLAN ON BOTH BUILDING SWITCH.  THE CONNECTION IN BETWEEN TWO SWITCHES IS CALLED TRUNK.  TRUNK HAS TWO PROTOCOL :-  Q - IT IS AN OPEN STANDARD AND PART OF IEEE. ( BY DEFAULT IT IS ENABLED ON CISCO SWITCHES, NOT IN CISCO ROUTERS ).  2. ISL – INTER SWITCH LINK

 IF YOU BUY A NEW SWITCH HAVING FACTORY DEFAULT SETTING, ALL THE PORTS CONFIGURED BY DEFAULT IS PART OF DEFAULT VLAN1.  EACH VLAN HAVE ITS OWN SAPRATE NETWORK OR SUBNET THAT WE CAN CREATE.  IF YOU HAVE 2 PC CONNECTED TO SWITCH WITH DIFFERENT VLAN THEY CANNOT COMMUNICATE EVEN THEY HAVE SAME SUBNET IP ADDRESS.  VLAN TAGED – ANY DATA COMING FROM SWITCH 1 VLAN 20 TO SWITCH 2, THE VLAN TAGED INFORMATION IS RECEIVED ON SWITCH 2 AND SWITCH 2 PASS THIS DATA ONLY TO VLAN 20 PORTS.  YOU HAVE TO MAKE YOUR TRUNK IN DOT1.Q ENCAPSULATION THEN IT WILL BE ABLE TO READ VLAN TAGS.

VLAN CONFIGURATION AND SHOW COMMANDS  AFTER COMPLETING BASIC CONFIGURATION ON SWITCH.  CREATE VLAN  Switch(config)#vlan 10  ASSIGN NAME TO VLAN  Switch(config)#vlan 10  Switch(config-vlan)#name sales  ADDING PORT IN VLAN  Switch(config)#int f0/1  Switch(config-if)#switchport mode access  Switch(config-if)#switchport access vlan 10  CHECK VLAN INFORMATION  Switch#sh vlan brief

MANAGEMENT IP  EVERY VLAN MUST HAVE ITS OWN MANAGEMENT IP WITH IN THE SUBNET.  WITH THE HELP OF MANAGEMENT IP’S WE CAN MANAGE SWITCH FROM EVERY VLAN PC.  COMMANDS FOR ASSIGN MANAGEMENT IP IN VLAN.  Switch(config)#int vlan 10  Switch(config-if)#ip address  Switch(config-if)#no shutdown

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