Chapter 16 Connecting LANs Backbone Networks and Virtual
Chapter 16 Connecting LANs, Backbone Networks, and Virtual LANs Kyung Hee University 1
16. 1 Connecting Devices q Repeaters q Hubs q Bridges q Two-Layer Switches Kyung Hee University 2
Connecting Devices q Kyung Hee University 3
Repeater • Repeater only operates in the physical layer • Repeater regenerates the signal • Doesn’t connect two LANs, connects two segments of the same LAN Kyung Hee University 4
Repeater q A repeater connects segments of a LAN. q A repeater forwards every frame; it has no filtering capability q A repeater is a regenerator, not an amplifier. Kyung Hee University 5
Function of Repeater • Must be placed so that a signal reaches it before noise changes the meaning of its bits Kyung Hee University 6
Hubs • Hub is a multiport repeater • Creates connections between stations in a physical star topology Kyung Hee University 7
Bridge q Bridge operates in both the physical and the data link layers q As a physical layer device, it regenerates the signal q As a data link layer device, it checks the physical (MAC) addresses Kyung Hee University 8
Bridge q A bridge has a table used in filtering decisions. Kyung Hee University 9
Bridge Kyung Hee University 10
Bridge q A bridge does not change the physical (MAC) addresses in a frame. q Transparent Bridge v. Bridge in which stations are completely unaware of the bridge’s existence v System equipped with transparent bridges must meet three criteria (IEEE 802. 1 d): l l l Frames must be forwarded from one station to another Forwarding table is automatically made by learning from movements Loops must be prevented Kyung Hee University 11
Learning Bridges Kyung Hee University 12
Loop Problem Kyung Hee University 13
Prior to spanning tree application Kyung Hee University 14
Applying spanning tree • Bridge with smallest ID is the root bridge • Mark one port of each bridge as the root port – port with the least -cost path from the bridge to the root bridge • Choose a designated bridge for each LAN – has the least-cost path between the LAN and the root bridge – make the corresponding port the designated port • Mark the root port and designated port as forwarding ports, the Kyung Hee others as blocking ports University 15
Forwarding ports and blocking ports • Dynamic algorithm – spanning tree algorithm is done dynamically with software in the bridge using Bridge Protocol Data Unit (BPDU) Kyung Hee University 16
Bridges Connecting Different LANs q Bridge should be able to connect LANs using different protocols, issues to be considered: v Frame format – Ethernet vs. wireless frame v Max data size – too large frames must be fragmented into several frames; no protocol at the data link layer allows for fragmentation and reassembly of frames v Data rate – each LAN has its own data rate v Bit order – some send most significant bit first, some send least significant first v Security – wireless has security measures at the dl layer, Ethernet does not v Multimedia support – some support, some do not Kyung Hee University 17
16. 2 Backbone Networks q Bus Backbone q Star Backbone q Connecting Remote LANs Kyung Hee University 18
Bus Backbone q In a bus backbone, the topology of the backbone is a bus. q Normally used to connect different buildings in an organization q Bridge blocks frames sent internally to the LAN q Backbone receives frame if going from one LAN to another Kyung Hee University 19
Star Backbone q In a star backbone, the topology of the backbone is a star; the backbone is just one switch. • Used as distribution backbone inside a building Kyung Hee University 20
Connecting remote LANs Kyung Hee University 21
Connecting remote LANs q. A point-to-point link acts as a LAN in a remote backbone connected by remote bridges. Kyung Hee University 22
Virtual LANs Kyung Hee University 23
A switch using VLAN software Kyung Hee University 24
Two switches in a backbone using VLAN software Kyung Hee University 25
VLAN q. VLANs create broadcast domains. Kyung Hee University 26
Questions ! Kyung Hee University 27
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