1 Fall 2005 Layer 3 Switches and VLANs Qutaibah Malluhi CSE Department Qatar University

2 Layer Three Switches  We have discussed what is called Layer 2 switches –They are like multi-port bridges –They work on frames (layer 2)  Layer-3 switches work on higher level packets (IP packets) –Like routers which are discussed later on.

3 Network Device Summary

4 Virtual LANs (VLANs)  VLANs are Local area network configured by software, not by physical wiring

5 Virtual LANs  Divides a LAN into logical, instead of physical, segments  Consider the need to move a machine from one LAN to another –Difficult with physical LANs (move machine, rewire, etc.) –Easy with VLANs (change configuration)  Even allows grouping of stations connected to different switches in a VLAN  Supports multiple broadcast domains, just as if stations belong to the same physical segment

6 Switches in a VLAN Backbone

7 VLAN Membership  May be classified by –Switch port numbers »Configure a group of ports to be part of the same VLAN –MAC addresses »Configure a group of MAC addresses to be part of the same VLAN –IP addresses »Configure a group of IP addresses to be part of the same VLAN –Combination of two or more

8 Advantages of VLANs  Cost and time reduction in moving stations from one group to another  Broadcast domains –impact on improving performance  Administrative advantages: –Creation of virtual workgroups  Security (privacy)  Performance management –E.g. the costly back-up on a separate VLAN to avoid slowing down standard operation

9 Summary  LANs –Have distance limitations –Can be extended  Optical fiber and modems can be used to extend AUI for single station  Repeater –Connects two LAN segments –Repeats and amplifies all signals –Forwards noise and collisions  Bridge –Understands and forwards entire frames –Uses addresses –Does not forward noise or collisions –Filtering bridges forward frames only as needed »Allows simultaneous transmission on the segments – Therefore, careful design can improve the performance. »Forwards all broadcast and multicast frames –DST used to break cycles

10 Summary (cont’d)  Hub –Central facility in star-shaped network –Operates like a repeater  Switch –Central facility in star-shaped network –Operates like a set of bridged segments –More expensive that a hub but provide higher aggregate bandwidth