Network Components

Internetworking

• Internetworking is a comprehensive term for all the concepts, technologies, and generic devices that allow people and their computers to communicate across different kinds of networks • Some Internetworking Devices are: • Repeaters • Bridges • Switches • Routers • Gateways 2

Repeater

• Repeaters work at the OSI physical layer to regenerate the network’s signal and resend them to other segments • A Repeater is the simplest and the least expensive internetworking device. It copies every messages it hears on LAN #1 to LAN #2, sometimes unnecessarily. • Used when you need to go farther distances than the cabling will allow • Usually has 2 ports (IN/OUT) 3

Hub • Primitive hub can be viewed as a multiport repeater • It regenerates data and broadcasts them to all ports • A central point of a star topology • Allows the multiple connection of devices • Functions in a similar manner to a Repeater • Works at the Physical Layer of the OSI model • Propagates each incoming signal to all connections • Does not understand packets • Multiple stations share one network connection

Hubs connecting segments

Bridge

• Like a Repeater or Hub it connects segments • Works at Data Layer – not Physical • Uses Mac address to make decisions • Acts as a ’filter’, by determining whether or not to forward a packet on to another segment

Bridges

A bridge can be used to connect two similar LANs, such as two CSMA/CD LANs.

A bridge can also be used to connect two closely similar LANs, such as a CSMA/CD LAN and a token ring LAN.

The bridge examines the destination address in a frame and either forwards this frame onto the next LAN or does not.

The bridge examines the source address in a frame and places this address in a routing table, to be used for future routing decisions.

Bridge

• Builds a Bridging Table, keeps track of devices on each segment • Filters packets, does not 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 • Bridges help to localize network traffic by only forwarding data onto other segments as required (unlike repeaters)

A bridge interconnecting two dissimilar LANs

Bridge interconnecting two identical LANs

Illustration of a Bridge

• Bridge uses source address to learn location of computers • Learning is completely automated

Illustration of a Bridge

Routing procedure for a transparent bridge: 1. If the destination and source LANs are the same, discard the frame.

2. If the destination and source LANs are different, forward the frame.

3. If the destination LAN is unknown, use flooding.

Remote Bridges

A remote bridge is capable of passing a data frame from one local area network to another when the two LANs are separated by a long distance and there is a wide area network connecting the two LANs.

A remote bridge takes the frame before it leaves the first LAN and encapsulates the WAN headers and trailers.

When the packet arrives at the destination remote bridge, that bridge removes the WAN headers and trailers leaving the original frame.

Two LANs with intervening frame relay network

Switches

• A switch is a combination of a hub and a bridge. • A multiport 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) • A switch improves network performance • Each port on a Switch is a collision domain When a frame arrives at a switch, the switch examines the destination address and forwards the frame out the one necessary connection.

•Workstations that connect to a hub are on a

shared segment

.

•Workstations that connect to a switch are on a

switched segment

.

Switch

• A multiport 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) • Similarly priced to Hubs – making them popular • Acts like a Hub, but filters like a Bridge • Each port on a Switch is a collision domain

Workstations connected to a shared segment of a LAN

Workstations connected to a dedicated segment of a LAN

A Switch with Two Servers Allowing Simultaneous Access to Each Server

A server with two NICs and two connections to a switch

A pair of remote bridges and switch combination designed to isolate network traffic

Switch providing multiple access to an e-mail server

Routers

A “router” is a device that operates at the network layer of the OSI model It supports multiple protocols (such as TCP/IP, IPX), and can be used to link LANs together locally or remotely as part of a WAN

Router

• Can connect different network segments, if they are in the same building or even on the opposite side of the globe • Work in LAN 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

Characteristics of Routers

• Expensive piece of hardware • Comes with its own administrative burden • Can slow down the network • Have a lower packet-filtering-and-forwarding rate as compared to switches • Protocol-dependent and cannot handle protocols that are not routable • The move now is towards implementing “switching routers” 25

Router

• 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 eg RIP

Gateway

• A Gateway is an inter-networking device that connects two or more computer networks that use different communications architectures • Allows different networks to communicate by offering a translation service from one protocol stack to another • They work at all levels of the OSI model – due to the type of translation service they are providing • Address Gateway – connects networks using the same protocol. • Protocol Gateway – connects network using different protocols. Translates source protocol so destination can understand it • Application Gateway – translates between applications such as from an Internet email server to a messaging server