1 Networking Devices MEENAKSHI SOOD LECT ECE NIT HAMR

MS2 Introduction Network Segments NICs Repeaters Hubs Bridges Switches Routers and Brouters Gateways

MS3 Network Segments No exact definition, usually an area of a LAN, or LAN More the devices which are added to the network, more the traffic – more chances of collision. Dividing network into segments allows the majority of traffic to stay remain local

MS4 Collision Domains Collisions occur when two or more devices transmit at the same time. This causes the electrical charge of the signal to increase – a collision All devices in the same collision domain cease transmitting for a random amount of time – to ensure they do not attempt to start transmitting at the same time again

Network Interface Card (NIC) NIC is an expansion card used to connect a PC, server, or workstation to a LAN NIC provides an interface between the network and the PC’s bus Most NICs are designed for a particular type of network, protocol, and media The NIC segments outgoing messages into packet formats specified by the LAN protocol for transmission MS5

MS6 At source: Receives the data packet from the Network Layer Attaches its MAC address and destination MAC address to the data packet Converts data into packets suitable for particular network (Ethernet, Token Ring, FDDI) Converts packets into electrical, light or radio signals Provides physical connection to media

MS7 Network Interface Card (NIC) (2) As a destination device Provides the physical connection to the media Translates the signal into data Reads the MAC address to see if it matches its own address If it does match, passes the data to the Network Layer

Repeaters, Hubs, Bridges, Switches, Routers and Gateways (a) Which device is in which layer. (b) Frames, packets, and headers.

What is a Repeater? Repeaters are low-level devices that amplify or regenerate weak signals Repeaters are needed to provide current to drive long cables Repeaters are used to join network segments together to increase the total length of the network Act at the physical layer and allow all traffic to cross LAN MS9

MS10 Repeater Extends the network beyond the maximum length of a single segment Functions at the Physical Layer of the OSI model Act as two port node A repeater is a regenerator.

02/07/2016Networks11 –There is a distance limitation on Ethernets (802.3) because the electrical signal becomes weaker as it travels along a wire. –To overcome this limitation, a repeater can be used to allow two cables to be joined together. –When a repeater sense a signal on one cable, the repeater transmits an amplified copy on the other cable. –Repeaters do not understand the frame format, they only deals with electrical signals.

Cont…. It forwards every frame but it has no filtering capability It does not amplifies the signal but regenerates it (original strength) Location of repeater is vital, should be placed so that signal reaches it before any noise changes the signal.

02/07/2016Networks13 The length of a Ethernet cannot be increased indefinitely by using multiple repeaters. –The reason for this is because Ethernet uses Carrier Sense Multiple Access with Collision Detection (CSMA/CD). –If the time it takes for a frame to propagate from one end of the network to the other end increases, it reduces the possibility of the computers connected to the cable being able to detect collisions. –802.3 standard specifies that the network may not operate correctly if more than four repeaters are used.

MS14 Advantages and Disadvantages Advantages – Can connect different types of media, can extend a network in terms of distance Disadvantages – Extends the collision domain, can not filter data, can not connect different network architectures It connects two segments of same LAN, it does not connect LAN with different protocols

What is a Hub? A place of convergence where data arrives from one or more directions and is forwarded out in one or more other directions Hub is a repeater with fault detection functionality It connects high-performance stations/devices to Ethernet local area networks and provides high- performance inter-LAN connectivity using switching technology A hub usually includes a switch of some kind MS15

MS16 Hub A central point of a star topology Allows the multiple connection of devices Can be more than a basic Hub – providing additional services (Managed Hubs, Switched Hubs, Intelligent Hubs) In reality, a Hub is a Repeater with multiple ports Functions in a similar manner to a Repeater

MS17 Hub (2) Works at the Physical Layer of the OSI model Passes data no matter which device it is addressed to A signal coming into the hub on a particular port is propagated to all other ports. This feature adds to congestion Can also be used to create multiple levels of hierarchy

MS18 Advantages and Disadvantages(2) Adv – Cheap Disadv – Extends the collision domain, can not filter information, passes packets to all connected segments

02/07/2016Networks19 –Bridges are used to connect two or more LANs together into one big LAN. –Why do we need bridges? LAN’s in different departments may have developed independently. Eventually they may need to be connected. Organisations may have LANs in different buildings, a bridge is needed to connect them. If a LAN is very busy, it may need to be split into a number of LANs to handle the load better (reduce collisions). Bridges

What is a Bridge? Connects a local area network (LAN) to another LAN that uses the same protocol (for example, Ethernet or Token Ring) A bridge works at the data-link level of a network, copying a data frame from one network to the next network along the communications path. Bridges can make minor changes to the frame before forwarding it(such as adding and deleting some fields from the frame header) MS20

MS21 Bridge Works at Data Layer and Physical Layer Uses MAC address to make decisions Acts as a ’filter’, by determining whether or not to forward a packet onto another segment

Two basic Ethernet networks connected by a bridge

MS23 Bridge (2) Builds a Bridging Table, keeps track of devices on each segment Filters packets, does forward them, by examining their MAC address It forwards packets whose destination address is on a different segment from its own It divides a network in to multiple collision domains – so reducing the number of collisions

MS24 Bridge (3) Uses the Spanning Tree Protocol (STP) – to decide whether to pass a packet on to a different network segment A Transmits to C, bridge will not pass it to Segment B G Transmits to B, bridge will pass it to Segment A

Cont…. Bridges increase the possibility of reliability in the network. Bridges are good for security, as they can be programmed to avoid forwarding sensitive traffic.

02/07/2016Networks26 Diagram of a bridge Data Link Network MAC Physical Host A Host B Bridge Packet CSMA/CD LAN Token Ring LAN

02/07/2016Networks27 Explanation of diagram –Host A has a packet to send –The packet is passed to the Data Link Layer and gets a sequence number etc. –This is then passed to the MAC sub-layer, which adds information relevant to A frame is created at this point. –The frame is passed to the physical layer, which places it on the cable as a sequence of 1’s and 0’s. –The frame arrives at the bridge and is eventually passed up to the MAC sub-layer where the specific information is stripped off. –The bare packet is handed to the Data Link Layer.

The Data Link Layer sends the packet down a different protocol stack, in this case The frame is eventually sent to the other LAN. Note: It is important to remember that a bridge connecting different types of Local Area Networks will have:  Different MAC sub-layers for each type of LAN  Possibly different physical layers

LEARNING PROCESS Routing table is maintained Static ( manually entries in the table were done ) Dynamic ( automatic updating) Automatic building of routing tables, use the Backward Learning Algorithm.

Backward Learning Algorithm The routing table consists of addresses of computers and the LAN that they are connected to.  Both source and destination address are inspected for a match in the table. Every frame they receive, for which the Bridge does not have a destination address in their routing table, are forwarded to all LANs except the one that it comes.

Before the Bridge forwards the frame, it makes an entry in its routing table for the computer sending the frame (source address in the frame). As part of this routing table entry, the Bridge notes the position of the sending computer, i.e. what LAN the sending computer is connected to. It uses this information for future reference, if another computer is sending frames to that particular computer. As more frames are received by the Bridge, the routing table at the Bridge fills up. As the routing table increases in size, the need to carry out flooding is reduced.

TRANSPARENT BRIDGE It is a bridge in which stations are completely unaware of the bridge’s existence. Reconfiguration is not required when bridge added or deleted. IEEE 802.1D

02/07/2016Networks33 –If we have a site with multiple LANs, we can plug these LANs into a Transparent Bridge and everything starts working. –There is no need to make hardware or software changes, no address setting, no manual building of routing tables. –The Transparent Bridge should operate using ‘plug and play’ –The most important part of Transparent Bridges is its automatic building of routing tables, using the Backward Learning Algorithm.

02/07/2016Networks34 Example Transparent Bridge G H A B C B1 B2 D B3 E F Transparent Bridge B2’s routing table would list the address of host A as being on LAN 2. It doesn’t need to know where it is on LAN 2 LAN 1 LAN 2 LAN 3 LAN 4

02/07/2016Networks35 High Speed LANs –The LANs that have been covered so far are mainly low speed and good only over short distances. –The future of LANs lie with faster transmission over greater distances and with greater reliability. –Two high speed LAN technologies of interest are FDDI: Fiber Distributed Data Interface, based on Optical Fiber Fast Ethernet, 802.3u, based on Twisted Pair and Optical Fiber.

Use of a central LAN switch in a star network architecture

LAN-to-LAN and LAN-to-MAN/WAN switches

LOOP PROBLEM Redundant Bridges are used to make system more reliable In case of failure of any bridge, another bridge takes over. Leads to Loop problem (bcoz of flooding technique)

Spanning Tree Bridges Two parallel transparent bridges.

Spanning Tree Bridges (2) (a) Interconnected LANs. (b) A spanning tree covering the LANs. The dotted lines are not part of the spanning tree.

MS41 Advantages and Disadvantages (3) Bridge Advantages – Limits the collision domain, can extend network distances, uses MAC address to filter traffic, eases congestion Disadvantages – Broadcast packets can not be filtered, more expensive than a repeater, slower than a repeater – due to additional processing of packets

Bridges connecting Different LANs LANs using different protocols at the Data Link Layer Certain issues to be considered *Frame Format *Maximum data size *Security *Data Rate

MS43 Switch A multi-port Bridge, functioning at the Data Link Layer Each port of the bridge decides whether to forward data packets to the attached network Keeps track of the MAC addresses of all attached devices (just like a bridge) Acts like a Hub, but filters like a Bridge Each port on a Switch is a collision domain

MS44 Advantages and Disadvantages (4) Switch Advantages - Limits the collision domain, can provide bridging, can be configured to limit broadcast domain Disadvantages – More expensive than a hub or bridge, configuration of additional functions can be very complex

The basic concept of an Ethernet switch

Repeaters, Hubs, Bridges, Switches, (a) A hub. (b) A bridge. (c) a switch.

MS47 Router Works at Network Layer in an intelligent manner Can connect different network segments, if they are in the same building or even on the opposite side of the globe Work in LAN, MAN and WAN environments Allows access to resources by selecting the best path Can interconnect different networks – Ethernet with Token Ring Changes packet size and format to match the requirements of the destination network

What is a Router? Routers determine the next network point to which a packet should be forwarded on the way to its final destination Routers use the Network Layer Protocol Information within each packet to "route" it from one destination or LAN to another –This means that a router must be able to recognize all the different Network Layer Protocols that may be used on the networks it is linking together Routers communicate with one another to determine the best route through the complex connections of many LANs to increase speed and cut down on network traffic MS48

MS50 Router (2) Two primary functions – to determine the ‘best path’ and to share details of routes with other routers Routing Table – a database which keeps track of the routes to networks and the associated costs Static Routing – routes are manually configured by a network administrator Dynamic Routing – adjust automatically to changes in network topology, and information it receives from other routers Routing Protocol – uses a special algorithm to route data across a network e.g., RIP

MS51 Advantages and Disadvantages (5) Router Advantages – Limits the collision domain, can function in LAN or WAN, connects differing media and architectures, can determine best path/route, can filter broadcasts Disadvantages – Expensive, must use routable protocols, can be difficult to configure (static routing), slower than a bridge

MS53 Brouter Functions both as Bridge and a Router – hence name Can work on networks using different protocols Can be programmed only to pass data packets using a specific protocol forward to a segment – in this case it is functioning in a similar manner to a Bridge If a Brouter is set to route data packets to the appropriate network with a routing protocol such as IP, it is functioning as a Router

The distinction between a bridge and a router

GATEWAY Operates in all the layers Used as connecting device between two internetworks that use different models. Provides security (as works up to the application layer)

MS56 Gateway Address Gateway – connects networks using the same protocol. Protocol Gateway – connects network using different protocols. Translates source protocol so that destination can understand it Application Gateway – translates between applications such as from an Internet server to a messaging server