VLAN...

What is VLAN ?..

Vlan is a group of hosts with a common set of requirements that communicate as if they were attached to the same broadcast domain, regardless of their physical location

·         Virtual Local Area Network

·         It is a logical  boundary on the switch

·         All the ports in a vlan can communicate with each other

·         The ports in different vlans cannot communicate in L2 switch

·         Inter vlan communication is possible in L3 switch

·         The ports with same vlan id can communicate even though they belong to different switches

·         Vlan range  is 1 – 1005

·         Vlan breaks the broadcast domain In the switch

·         Vlan manage the information only on a single switch

·         To communicate data across the multiple switches we need VTP

·         Logically groups users

·         Segments broadcast domains

·         Subnet correlation

·         Access control

·         Quality of service

What is Default VLAN?

·         By default a vlan exit on the switch with vlan id 1

·         This Vlan 1 is called as default valn or management vlan

·         By default all the ports belong to vlan 1 in the switch

·         Vlan 1 can’t be created or deleted

·         Generally vlan 1 carries management information like cdp, vtp

What is management VLAN?

·         The active vlan to which ip address is assigned and operational

·         Management vlan carries switch management information

·         By default vlan 1 is management vlan

What is Trunking?

·         The link between different switches that can carry the data from various vlans

Switches port types:

        Access port

·         Used to connect a computer

·         Access port can understand normal Ethernet frame

·         Access port belongs to only one vlan

Trunk port

·         Used to connect a switch

·         Trunk port can understand tagged Ethernet frames

·         Trunk port can be a member of multiple vlans

·         Trunk port minimum speed is 100Mbps

What is frame tagging?

·         Trunk port inserts vlan id information within the frame before sending it through trunk link

·         Trunk port removes vlan id information from the frame before sending it to system

Tagging vlan id information to the original Ethernet frame is called frame tagging or frame encapsulation

Frame tagging methods

·         Dot 1 q

·         ISL

Difference between dot 1 q and ISL

Dot 1 q	ISL
IEEE 802.1q encapsulation	Inter switch link
Open standard	Cisco proprietary
Insert vlan id within the frame	Encapsulates Ethernet frame with new header & tailor
Insert 4 bytes	Header is 26 bytes, tailor is 4 bytes
Original frame size is 1518 bytes new frame size is 1522 bytes	Original frame size is 1518 bytes new frame size is 1548 bytes

What is native VLAN?

·         The vlan from which frames are not tagged

·         By default vlan 1 is native vlan

·         Native vlans must match at both ends of trunk link

·         Native vlans occur only when we using 802 1Q does not occurs in ISL

Servers at trunk ports:

·         The ports from different vlans may need to access common servers

·         Servers with trunk NIC can be connected at trunk ports

·         Trunk NIC can understand tagged frames