1. Virtual LANs and trunking
VLANs
Virtual LANs and trunking

2. VLANs Define LAN & VLAN Examples Tagging / trunking
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
Sales=1, finance=2, support=3, R&D=4
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
DstEaddr
SrcEaddr
EType
Data
FCS
DstEaddr
SrcEaddr
VLAN Etype
VLAN TAG
EType
Data
FCS
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