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VLANs By: Mahdi Nasereddin Ph.D.

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VLAN?

 A Virtual Local Area Network is a logical grouping of network users and resources connected to administratively defined ports on a switch.

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Why use VLANs?

   Layer 2-switched networks are flat  One big broadcast domain Flexibility Security  Anybody connected to the physical network could access network resources.

 With VLAN, Administrator control the ports

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Flat Network

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Flexibility

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Flexibility

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VLAN Membership  Static VLAN  Typical way of creating VLAN  Ports are assigned by the administrator  Dynamic VLAN  Automatic port assignment (you have to create a MAC lookup table)  Uses Intelligent Management Software (Example: Cisco’s VMPS)

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Link Types in a switched Environment  Access links  Part of one VLAN  Devices attached to access links don’t realize that they are connected to a VLAN  In order to communicate with devices on other VLANs, the packets have go through a router

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Link Types in a switched Environment (cont.)  Trunk links  Carry multiple VLANs  Used to connect switches to other switches, routers, or servers.

 Runs on fast or gigabyte Ethernet only  Contain a default VLAN “used if the trunk link fails”

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Trunk Link