1 25\10\2010 Unit-V Connecting LANs Unit – 5 Connecting DevicesConnecting Devices Backbone NetworksBackbone Networks Virtual LANsVirtual LANs

2 25\10\2010 Unit-V Connecting LANs CONNECTING DEVICES 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

3 25\10\2010 Unit-V Connecting LANs 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) Connecting Devices

4 25\10\2010 Unit-V Connecting LANs 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 Passive Hub

5 25\10\2010 Unit-V Connecting LANs 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 Repeater

6 25\10\2010 Unit-V Connecting LANs forwards every frame; it has no filtering capability. It does not amplify the signal it regenerates the signal Repeaters

7 25\10\2010 Unit-V Connecting LANs 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 Active Hubs

8 25\10\2010 Unit-V Connecting LANs HUB Devices HUB Repeater/Amplifier Active Hubs

9 25\10\2010 Unit-V Connecting LANs A hierarchy of hubs Active Hubs

10 25\10\2010 Unit-V Connecting LANs 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. Bridges

11 25\10\2010 Unit-V Connecting LANs A bridge connecting two LANs Bridges

12 25\10\2010 Unit-V Connecting LANs 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. Bridges

13 25\10\2010 Unit-V Connecting LANs 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. Bridges

14 25\10\2010 Unit-V Connecting LANs 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 Bridges

15 25\10\2010 Unit-V Connecting LANs 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. Bridges

16 25\10\2010 Unit-V Connecting LANs Loop problem in a learning bridge Bridges

17 25\10\2010 Unit-V Connecting LANs 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. Bridges

18 25\10\2010 Unit-V Connecting LANs Bridges The bridge with smallest ID is selected as root node. Assuming B1 has the smallest ID Bridge to LAN COST is 1 and LAN to Bridge cost is 0

19 25\10\2010 Unit-V Connecting LANs Finding the shortest paths and the spanning tree in a system of bridges Bridges

20 25\10\2010 Unit-V Connecting LANs Forwarding and blocking ports after using spanning tree algorithm Bridges

21 25\10\2010 Unit-V Connecting LANs 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 Switches

22 25\10\2010 Unit-V Connecting LANs 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 Switches

23 25\10\2010 Unit-V Connecting LANs Switches Interconnecting Wing C Wing AWing B First Floor Switch Switches

24 25\10\2010 Unit-V Connecting LANs 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 Routers

25 25\10\2010 Unit-V Connecting LANs Routers Interconnecting \ Router Ethernet LAN2 Token Ring LAN1 X.25 Network the “cloud” Routers

26 25\10\2010 Unit-V Connecting LANs Routers connecting independent LANs and WANs Routers

27 25\10\2010 Unit-V Connecting LANs 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 Gateways

28 25\10\2010 Unit-V Connecting LANs 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

29 25\10\2010 Unit-V Connecting LANs 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. Bus Backbone

30 25\10\2010 Unit-V Connecting LANs 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

31 25\10\2010 Unit-V Connecting LANs 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. Star Backbone

32 25\10\2010 Unit-V Connecting LANs 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.

33 25\10\2010 Unit-V Connecting LANs 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

34 25\10\2010 Unit-V Connecting LANs A switch connecting three LANs 10 stations grouped into 3 LANs, If two engineers need to move from grop1 to group3, rewiring is needed Connecting remote LANs

35 25\10\2010 Unit-V Connecting LANs A switch using VLAN software Connecting remote LANs

36 25\10\2010 Unit-V Connecting LANs Two switches in a backbone using VLAN software Connecting remote LANs

37 25\10\2010 Unit-V Connecting LANs Characteristic to group a stations in a VLAN Port Numbers: Switch port numbers. Ex stations connecting to ports 1,2,3, 7 to VLAN1 and stations connecting to ports 4,10, and 12 belong to VLAN2 MAC addresses: 48 bit MAC address IP addresses: 32 bit IP address Combination: Membership

38 25\10\2010 Unit-V Connecting LANs 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. Configuration