VLANs

1
VLANs

• Virtual LANs and trunking

2
VLANs

• Define LAN VLAN
• Examples
• Tagging / trunking
• Examples
• Seifert chapter 11/12

3
What is a LAN (in VLAN context)

• LAN is all ports that share same broadcast domain
• same ip subnet
• Broadcast domain important for PnP networks such
  as W9x/W19100
• Allows one to find network resources
  servers/printers/

4
Need for VLANs

• Classic approach (at least) one hub/switch per
  LAN
• Expensive / nonflexible
• Need to split up switch in multiple
  (independent) LANs
• Give each LAN a number
• Sales1, finance2, support3, RD4
• Assign each port to a specific VLAN
• Software patch panel

5
Trunking

• Desire to run multiple LANs on one and the same
  trunk
• One cable can feed multiple LANs/multiple groups
• Need to multiplex /demultiplex packets for
  different VLANs based on VLAN number
• Frame tagging
• Have to tag on ethernet level

6
Tagged Ethernet packets
Data
SrcEaddr
EType
DstEaddr
FCS
Data
SrcEaddr
EType
DstEaddr
FCS
VLAN Etype
VLAN TAG
Max ethernet packet size grows from 1514 to 1518
bytes
7
Different VLAN approaches

• Port-based mapping
• MAC-address based mapping
• Protocol-based mapping
• IP subnet-based mapping

8
Examples

• One-legged router
• Feed whole building with multiple LANs from
  router in other building
• Build individual subnets for endusers
• cablemodems/ADSL

9
Tech talk

• IEEE network standard 802.x
• Ethernet standard IEEE 802.3
• exists of 802.3a-z, 802.3aa-..
• VLAN standard IEEE 802.1Q
• ethernet independent
• Bigger packets IEEE 802.3ac