VLAN

LAN

o A LAN is a shared communication system to which many computers are attached.
o LAN is also defined as a single broadcast domain.
o Ethernet and Wi-Fi are the commonly used LAN technologies.

-> LANs are OSI layer 2 technologies.
-> LANs use arbitration method called CSMA/CD.
-> LANs contain their own broadcasts and addressing schemes.
-> The workstations, hubs, and repeaters together form a collision domain.
-> Bridges and switches limit collision, but will allow broadcasts and multicasts to pass through.
-> And the L3 device, router prevents broadcast and multicast from travelling across the network.

With the transmission speed Ethernet is further divided:

Ethernet   -> 10 Mbits/sec
Fast Ethernet   -> 100 Mbits/sec
Gigabit Ethernet  -> 1000 Mbits/sec
10Base-5  -> 10Mbps, Coaxial cable, 500 meters
10Base-T  -> 10Mbps, Twisted-pair cable, 100 meters
10Base-FL  -> 10Mbps, Fiber-optic cable, 4 Km

VLAN

o VLAN groups collection of machines in a logical and non physical way.
o VLANs allow a network manager to logically segment a LAN into different broadcast domains, irrespective of physical location.
o VLAN is defined as a broadcast domain within a switched network.

-> VLAN reduces the broadcast domain at the MAC layer.
-> VLAN restricts access to network resources.
-> Traffic from one VLAN to another is possible only through a router.

IEEE 802.1Q (VLAN Tagging or dot1q), Cisco’s Inter-Switch Link, 3Com’s Virtual LAN Trunk are the commonly used protocol to configure VLAN.



12bit VID = (4096-2) VLANs are possible in a switch.

Types of VLAN's:
VLAN membership can be classified by port, MAC address, and protocol type.

1. Layer 1 VLAN: Membership by Port
   a. User mobility is restricted.
2. Layer 2 VLAN: Membership by MAC Address
   a. Manual configuration of MAC and VLAN membership required.
3. Layer 2 VLAN: Membership by Protocol Type
   a. It’s based on protocol type field in L2 header.
4. Layer 3 VLAN: Membership by IP Subnet Address
   a. Static IP should be configured in PC.
5. higher layer VLAN: Membership by application type

Protocol type based, IP subnet based and higher layer application based VLAN are not mentioned in the standard, hence these VLANs remains proprietary.

The Nortel ERS4500 supports up to 256 VLANs.
The Nortel ERS4500 supports VLAN types:
1. IEEE 802.1Q port-based VLANs
   a. vlan create 16 name red type port
   b. vlan members remove 1 2-12
   c. vlan members add 16 2-12
   d. vlan ports 2-12 pvid 16
2. Protocol-based VLANs
   a. vlan create 16 name test type protocol-Netbios

VLAN support in Linux:
Networking options -> 802.1Q VLAN Support
This module generates driver with the name 8021q.o

modprobe 8021q
vconfig add eth0 16
ifconfig eth0.16 192.168.16.2 netmask 255.255.255.0
ping 192.168.16.1

it could be observed that all packets coming from eth0.16 is tagged with VLAN ID 16.

Ethernet II frame

+-----------+----------+----------+-----------+----------+
|Destination|Source MAC|Frame type|Data       | CRC      |
|MAC Address|Address   |(IP, ARP) |(46 to     | Checksum |
|(6 bytes)  |(6 bytes) |(2 bytes) |1500 bytes)| (4 bytes)|
+-----------+----------+----------+-----------+----------+

14(Ethernet) + 1500(DATA) + 4(CRC) = 1518
14(Ethernet) + 4(VLAN) + 1500(DATA) + 4(CRC) = 1522
14(Ethernet) + 4(vlan) + 20(IP) + 20(TCP) +1460(DATA) + 4(CRC)

Reference:
http://www.linktionary.com/l/lan.html