251020 Unit 5 Connecting Devices Backbone Networks Virtual

• • • 251020 Unit – 5 Connecting Devices Backbone Networks Virtual LANs Unit-V Connecting LANs 1

CONNECTING DEVICES In this section, connecting devices are divided into five different categories based on the layer in which they operate in a network. Passive Hubs Active Hubs Bridges Two-Layer Switches Routers Three-Layer Switches Gateways 251020 Unit-V Connecting LANs 2

Connecting Devices Five categories of connecting devices based on the layer in which they operate in a network 1. Those which operate below the physical layer (passive hub) 2. Those which operate at the physical layer (repeater or an active hub) 3. Those which operate at the physical & data link layer (bridge) 4. Those which operate at he physical & data link &network layer (router or 3 layer switch) 5. Those which operate at all the five layer (a gateway) 251020 Unit-V Connecting LANs 3

Passive Hub is a connector It connects the wires coming from different branches. same or different cable types pass on every message used to connect LANs of similar technology, or to extend the distance of one LAN 251020 Unit-V Connecting LANs 4

Repeater is a device that operates only in physical layer It does not connects two LANs, it connects segments of a LAN. It is used to extend the physical length of a LAN 251020 Unit-V Connecting LANs 5

Repeaters forwards every frame; it has no filtering capability. It does not amplify the signal it regenerates the signal 251020 Unit-V Connecting LANs 6

Active Hubs are a multiport repeater It is usually used to create connections between stations in a physical star topology limited distance between devices no protocol or rate conversion no error detection does not filter 251020 Unit-V Connecting LANs 7

Active Hubs HUB Devices Repeater/Amplifier HUB 251020 Unit-V Connecting LANs 8

Active Hubs A hierarchy of hubs 251020 Unit-V Connecting LANs 9

Bridges Operates in both the physical and the data link layer. The difference between bridge and repeater is that, it has filtering capability. Can physical (MAC) addresses contained in the frame. connect two LAN segments that use the same data link and network protocol same or different cable types forward only those messages that need to go out (filtering) “learn” whether to forward packets internal routing table combination of “black box” hardware and software A bridge has a table used in filtering decisions. A bridge does not change the physical (MAC) addresses in a frame. 251020 Unit-V Connecting LANs 10

Bridges A bridge connecting two LANs 251020 Unit-V Connecting LANs 11

Bridges There are three types of bridges: Simple bridge Learning bridge Multiport bridge Transparent Bridge A Transparent Bridge is bridge in which the stations are completely unaware of the bridge’s existence Transparent bridges must meet three criteria: 1. Frames must be forwarded from one station to another 2. Forwarding table must be automatically updated 3. Loops in the system must be prevented. 251020 Unit-V Connecting LANs 12

Bridges Learning: Bridges have forwarding tables. System administrator manually enter each table during bridge setup If a station is added, or deleted or MAC address changed which is not a rare event (Inserting a new network card). A solution to this is to map address to ports automatically. In this case table is dynamic in which bridge gradually updates addresses to ports automatically. 251020 Unit-V Connecting LANs 13

Bridges A learning bridge and the process of learning A sends frame to D, it flood in all ports but it notices A is in port 1 When E sends a frame to A it forwards only on port 1 and notices E is in port 3 B sends a frame to C it floods in all ports and notices B is in port 1 251020 Unit-V Connecting LANs 14

Bridges Loop problem Networks usually have redundant bridges to make system more reliable If bridge fails another bridge takes over until the failed one is repaired or replaced Redundancy can create loops in the system, which is very undesirable. 251020 Unit-V Connecting LANs 15

Bridges Loop problem in a learning bridge 251020 Unit-V Connecting LANs 16

Bridges Spanning Tree In a graph theory, a spanning tree is graph in which there is no loop but all the elements of the graph are connected. In this case, creating bridged network in which LAN can be reached from any other LAN through one path only. Network consists of 4 LANS and 5 bridges To find a spanning tree a cost (metric) is used. Cost may be minimum hops, minimum path delay or path with maximum bandwidth. 251020 Unit-V Connecting LANs 17

Bridges • The bridge with smallest ID is selected as root node. • Assuming B 1 has the smallest ID • Bridge to LAN COST is 1 and LAN to Bridge cost is 0 251020 Unit-V Connecting LANs 18

Bridges Finding the shortest paths and the spanning tree in a system of bridges 251020 Unit-V Connecting LANs 19

Bridges Forwarding and blocking ports after using spanning tree algorithm 251020 Unit-V Connecting LANs 20

Switches Connect more than two LAN segments that use the same data link and network protocol. Switches • Two Layer switch • Three Layer switch Two Layer switch • Performs at physical and data link layer • Ex Bridge, can connect a few LANs together • Makes filtering decision based on MAC address Three Layer switch • Performs at Network layer • Ex, Routers 251020 Unit-V Connecting LANs 21

Switches Cut-through switches • use circuit-switching to immediately connect the port with the incoming message to the correct outgoing port • very fast as decisions are done in hardware • outgoing packet is lost if port is in use Store-and-forward switches • copy the incoming packet to memory prior to processing the destination address -- transmit it when the outgoing port is ready 251020 Unit-V Connecting LANs 22

Switches Interconnecting Wing A Wing B First Floor Switch Wing C 251020 Wing C Unit-V Connecting LANs 23

Routers Connect two or more LANs that use the same or different data link protocols, but the same network protocol. Same or different cable types Operate at the network layer Forward only messages that need to go out Routers use internetwork address (IP or Logical address) Internal routing tables Only processes messages addressed to it 251020 Unit-V Connecting LANs 24

Routers Interconnecting Router X. 25 Network Ethernet the “cloud” LAN 2 Token Ring LAN 1 251020 Unit-V Connecting LANs 25

Routers connecting independent LANs and WANs 251020 Unit-V Connecting LANs 26

Gateways is normally a computer that operates in all five layers of the Internet or seven layers of OSI model complex machines that are interfaces between two or more dissimilar networks Connecting device between tow internetworks that use different models (one with OSI and other with Internet model) connect two or more LANs that use the same or different data link layer, network layer, and cable types forwards only those messages that need to go out a combination of both hardware and software translates one network protocol to another translates data formats translates open sessions between application programs Gateways can provide security 251020 Unit-V Connecting LANs 27

BACKBONE NETWORKS A backbone network allows several LANs to be connected. In a backbone network, no station is directly connected to the backbone; the stations are part of a LAN, and the backbone connects the LANs. Bus Backbone Star Backbone Connecting Remote LANs 251020 Unit-V Connecting LANs 28

Bus Backbone In a bus backbone, the topology of the backbone is a bus. Normally used as a distribution backbone to connect different buildings in an organization. Each building may have single LAN or another backbone(star). Ex: single or multiple floor buildings on a campus, each single floor usually has a single LAN, each multiple floor building has a backbone (star) that connect each LAN. A bus backbone can interconnect these LANs and backbone. 251020 Unit-V Connecting LANs 29

Bus Backbone Frame within a LAN will not be allowed go out by bridge. If a station needs to send frame to station in another LAN the bridge passes the frame to the backbone which is received by the appropriate bridge and is delivered to the destination LAN 251020 Unit-V Connecting LANs 30

Star Backbone In a star backbone, the topology of the backbone is a star; the backbone is just one switch. Star backbone are mostly used as backbone inside a building. In a multifloor building, there is one LAN for each floor, and star backbone connects these LANs. 251020 Unit-V Connecting LANs 31

Connecting remote LANs A point-to-point link acts as a LAN in a remote backbone connected by remote bridges. Company has several offices need to be connected. 251020 Unit-V Connecting LANs 32

VIRTUAL LANs Virtual local area network (VLAN) is defined as a local area network configured by software, not by physical wiring. Membership Configuration Communication between Switches IEEE Standard Advantages 251020 Unit-V Connecting LANs 33

Connecting remote LANs A switch connecting three LANs 10 stations grouped into 3 LANs, If two engineers need to move from grop 1 to group 3 , rewiring is needed 251020 Unit-V Connecting LANs 34

Connecting remote LANs A switch using VLAN software 251020 Unit-V Connecting LANs 35

Connecting remote LANs Two switches in a backbone using VLAN software 251020 Unit-V Connecting LANs 36

Membership Characteristic to group a stations in a VLAN Port Numbers: • Switch port numbers. Ex stations connecting to ports 1, 2, 3, 7 to VLAN 1 and stations connecting to ports 4, 10, and 12 belong to VLAN 2 MAC addresses: • 48 bit MAC address IP addresses: 32 bit IP address Combination: 251020 Unit-V Connecting LANs 37

Configuration How are the stations are grouped into different VLANs Manual configuration: • Network administrator uses VLAN software to manually assign the stations into different VLANs at setup, based on characteristic. Manually means administrator types the port numbers, IP address … Automatic configuration: • Administrator groups stations based on the project working. 251020 Unit-V Connecting LANs 38