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VLANs
- Break up flat layer-2 networks.
- Several broadcast domains (usually 1 per VLAN) instead of a single
one
- Provide possible redundancy & load balancing
- logical networks over a physical network segment
- Can span over several switches (Campus-wide)
- Needs Layer 3 routing (Router or Layer 3 switch)
- VLAN numbers from 1 to 1005
- VLAN 1 is the default VLAN, 1002-1005 for legacy functions
- Numbering from 1 - 4094 (extended-range) in compatibility with 802.1Q only
in VTP transparent mode
VLAN Membership
- Static (port based)
- Dynamic (MAC based, needs VMPServer)
Static VLANs
- Easy to configure
- Difficult to manage in big networks with changing/moving workstations
Dynamic VLANs
- Not covered in BCMSN
- According to MAC address of connecting station
- Need a VLAN Membership Policy Server (VMPS)
Implementation of VLANs
- One VLAN per IP subnet (recommended)
- End-to-end VLANs (campus-wide VLANs) not recommended anymore
- Local VLANs because 80/20 becomes rather 20/80 in todays LANs
- Local VLANs to be contained within a Switch-Block
Trunks
- A switch port can only be in one VLAN at a time
- A trunk (switch port in trunk mode) can carry many different VLANs (even
though it's the same physical port)
- Trunk links can transport a number of VLANs between two switches or a
switch and a router
- Trunks can use fast- or Gigabit-Ethernet and EtherChannels
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