Virtual LANs and trunking VLANs Virtual LANs and trunking

VLANs Define LAN & VLAN Examples Tagging / trunking Seifert chapter 11/12

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/…

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’

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

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

Different VLAN approaches Port-based mapping MAC-address based mapping Protocol-based mapping IP subnet-based mapping

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

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