Internetworking

Internetworking

Hussain Ali, [email protected]

Department of Computer Engineering King Fahd University of Petroleum and

MineralsDhahran, Saudi Arabia

What is Internetworking ? Internetworking stands for

connectivity and communication between two or more networks.

dropping the “s” from Networks.

How is Internetworking Achieved ?

Cables and physical interfaces (physical connectivity)

Protocols, management and applications needed to support user (Internetworking)

Motivation for Internetworking

Overcome distance limitations and protocol differences for more effective sharing of data and resources

Productive communication between people across a single network or multiple networksEmail, newsgroups, mailing lists, live conferencing

Components of an Internetwork

Campus NetworkLocally connected users in a building or group of

buildings Wide Area Networks (WANs)

Distant campuses connected together usually through connection providers such as the phone company

Remote ConnectionsLinking branch offices and mobile users to a

corporate campus

Campus Networks A campus is a building or group of buildings

all connected into one enterprise network that consists of many local area networks.

The distinct characteristic of a campus is that the company network owns the physical wires.

Campus network topology is primarily LAN technology connecting all the end systems together.

Campus networks generally use LAN technologies such as Ethernet, Token Ring, FDDI, Fast Ethernet, and ATM.

Wide Area Networks WAN communication occurs between

geographically separate areas. In enterprise internetworks, WANs connect

campuses together. When a local end station wants to

communicate with a remote end station, information must be sent over one or more WAN links.

WAN services are provided through the following 3 primary switching technologies:Circuit SwitchingPacket SwitchingCell Switching

Remote Connection Remote connections link single mobile users

and branch offices to a local campus. Typically a branch office is a small site that

has few users and needs a low bandwidth WAN connection.

These small sites or single users, seldom need to remain connected 24 hours a day.

Remote connections are generally dial-up links or low bandwidth dedicated WAN links.

Trends in LAN/WAN Integration

Today, most of the computing power resides on the desktop, and this power is growing.

Distributed applications are increasingly bandwidth hungry.

Voice communications have increased significantly.

All of this is driving towards an integration of LANs and WANS under one roof.

In the LAN, bandwidth is free and connectivity is limited only by hardware.

In the WAN, bandwidth is an excessive cost. The existence and development of bandwidth

sensitive traffic such as voice and real-time video has forced a requirement of better and more predictable LAN and WAN performance.

Interaction of Different Networks

1. LAN-to-LAN 2. LAN-to-WAN 3. WAN-to-WAN4. LAN-to-WAN-to-LAN

Host 802.5LAN

MR

SNA WAN

X.25 WAN

MR

B

MR

MR802.3 LAN802.4 LAN802.3 LAN

Host

Host

Host Host

B: Bridge MR: Multi-protocol routerHostHostHostHost

Devices that interconnect LANs are known as relays and operate at one layer of OSI model

There are four common types of relaysRepeater: at physical layer (bits)Bridge: at data-link layer (frames)Router: at network layer (packets)Gateways: at transport and higher

layers (protocols)

Relays

Repeater (Hub) Overcomes restrictions caused by single

segment usage such as number of users, cable length.

Amplifies or regenerates weak signals . Extends cable length Can connect LANs of a similar type but which

use different media. Provides simple connection between adjacent

LANs at the expense of increased network congestion

Use of Repeaters for a Multi-segment LAN

Repeater

Segment A

Segment B

StationPrinter

Station

StationsFile Server

Bridge Interconnects two or more LANs (either similar

or dissimilar) at the MAC level. Capable of deciding whether or not to forward

frame. Creates an extended network and keeps local

traffic off. Can make minor changes to frame header. Does not inspect or modify the network layer

packets inside frames.

Characteristics of Bridges

Routing Tables Filtering Forwarding Learning Algorithm

Routing tableContains one entry per station of network to

which bridge is connected.Is used to determine the network of

destination station of a received packet. Filtering

Is used by bridge to allow only those packets destined to the remote network.

Packets are filtered with respect to their destination and multicast addresses.

Forwarding: the process of passing a packet from one network to another.

Learning: the process by which the bridge learns how to reach stations on the internetwork.

Operation of a LAN bridge from 802.3 to 802.4

802.3 CSMA/CD 802.4 Token bus

Host A

LLC

MAC

Host B

PhysicalMAC

LLC

NetworkBridge

802.3Packet

802.3Packet

802.4

Packet

Packet

802.4Packet

802.4Packet

Packet

Packet

Packet

802.3

802.3

802.4

Physical

Network

Transparent Bridges The first IEEE 802 bridge is a transparent

bridge or spanning tree bridge. People wanted to have complete transparency:

when a site with multiple LANs buys bridges designed to the IEEE standard, just plug connectors into bridges. So,no need for hardware/software changes,no setting of address switches,no downloading of routing tables or

parameters.

A transparent bridge accepts every frame transmitted on all the LANs to which it is attached.

A BD

CF H

G

E

LAN 1 LAN 2 LAN 3

LAN 4

BridgeBridge

Topology can change dynamically. There must be only one path of bridges and

LANs between any two segments in the bridged LAN

Bridges must support Spanning Tree Protocol if network contains loops.

Have the advantage of being easy to install Use only a subset of topology. Are chosen by the CSMA/CD and token bus.

Source Routing Bridges Token ring people chose the source routing

bridge. Transmitter, or source, of frame in source

routing specifies which route the frame is to follow.

Every machine in the network knows, or can find, the best path to every other machine; discovery frame is used.

Sender knows whether or not the destination is on its own LAN.

Issue TransparentBridge

Source Routing Bridge

Orientation Connectionless Connection-orientedTransparency Transparent to

hostsNot transparent

Configuration Automatic ManualRouting Suboptimal OptimalLocatingDestinations

Backward learning Discovery frames

Failures Handled bybridges

Handled by hosts

Complexity In the bridges In the hosts

Comparison of Bridges

Router Provides a more intelligent service

makes a decision as to the best way to deliver a packet from source to destination

may fragment packets to meet packet size requirements of LANs

are slower than bridges Permits translation between different address

domains such as addresses of IEEE 802 LAN and X.25

Connects dissimilar networks, provided that end-systems use a common network layer protocol, such as IP.

Unlike bridge, router receive only those packets addressed to it by either a user machine or another router.

Select the best route. The question of who owns, operates, and

maintains a router arises especially when two networks belong to independent organizations.

Full Router and Two Half-Routers

Buffer

Net 1 to internet

Net 2 to internetNetwork 1 Network 2

internet to Net 1

internet to Net 2

Network 1 Network 2

Net 1 tointernet

Net 2 tointernet

internetto Net 2

internetto Net 1

Machine owned jointly by bothnetworks

Full Router:

Two-HalfRouters:

Disadvantages of Routers Routers

are protocol-dependent devices that must understand the protocol they are forwarding.

can require a considerable amount of initial configuration.

are relatively complex devices, and generally are more expensive than bridges.

Advantages of RoutersRouters provide sophisticated routing, flow

control, and traffic isolation are configurable, which allows network

manager to make policy based on routing decisions

allow active loops so that redundant paths are available

Gateway Connects end-systems whose host protocols

have varying degrees of difference Transport gateways make a connection

between two networks at the transport layer. Application gateways connect two parts of an

application in the application layer, e.g., sending email between two machines using different mail formats

Connect two networks above the network layer of OSI model.

Are capable of converting data frames and network protocols into the format needed by another network.

Provide for translation services between different computer protocols.

Routers versus Bridges Addressing

Routers are explicitly addressed. Bridges are not addressed.

AvailabilityRouters can handle failures in links, stations,

and other routers.Bridges use only source and destination

MAC address, which does not guarantee delivery of frames.

Message Size » Routers can perform fragmentation on

packets and thus handle different packet sizes.

» Bridges cannot do fragmentation and should not forward a frame which is too big for the next LAN.

Forwarding» Routers forward a message to a specific

destination.» Bridges forward a message to an outgoing

network.

Priority» Routers can treat packets according to

priorities» Bridges treat all packets equally.

Error Rate» Network layers have error-checking

algorithms that examines each received packet.

» The MAC layer provides a very low undetected bit error rate.

Security» Both bridges and routers provide the

ability to put “security walls” around specific stations.

» Routers generally provide greater security than bridges because–they can be addressed directly and–they use additional data for

implementing security.

Brouters: Bridging Routers Combine features of bridges and routers. Capable of establishing a bridge between two

networks as well as routing some messages from the bridge networks to other networks.

Are sometimes called (Layer 2/3) switches and are a combination of bridge/router hardware and software.

Network Connectivity Devices Entry-level Hubs

Interconnect PCs in a single network segmentSimple stand-alone device that provides a starting point

cost-effective connectivity for many organizations.

Network Connectivity Devices (contd.)

Stackable HubsLet you start small and grow your network at your own

pace.Are connected by flexible expansion cables, and once

stacked together, function as one hub.Manageable as one logical unit.


Chassis HubBig iron box that can contain a variety of network

modules.It has a power supply, a high speed backplane, and

expansion slots for plug-in Hub modules.


Workgroup switchesLow-end network devices that aggregate multiple

shared segmentsUse switching technologyTypically deployed at the desktop levelEthernet, Token-Ring, or ATM


Workgroup switchesLow-end network devices that aggregate multiple

shared segmentsUse switching technology.Typically deployed at the desktop level.


Backbone switchesHigh-end network devices deployed at the core of the

network.Use switching technology.Aggregate data from Hubs and Workgroup switches.Typically accept various networking options.


RoutersPerform routing of packets among LANs.Provide most effective way of segmenting the network.Move data by finding the best path from the sender to

the receiver.Suitable for organizations with many large LANs.

Internetworking

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