11

Local InternetsLocal Internets

Cabletron SmartSwitch 2100

22

Local InternetsLocal Internets

InternetInternet System of subnets such that any station on any System of subnets such that any station on any

subnet can communicate with any station on any subnet can communicate with any station on any other subnet by placing the receiver’s address in a other subnet by placing the receiver’s address in a messagemessage

Subnets are individual networks in an internetSubnets are individual networks in an internet

33

Local InternetsLocal Internets

Local InternetsLocal Internets Links multiple LANs at a single siteLinks multiple LANs at a single site

Entirely on customer premisesEntirely on customer premises

Planned and managed by the ownerPlanned and managed by the owner Company has no limitsCompany has no limits Company has all the headachesCompany has all the headaches

High-speed transmission (roughly LAN speeds)High-speed transmission (roughly LAN speeds)

LANLANLANLAN

LANLANLANLANLANLANLANLAN

LANLANLANLAN

44

Why a Local Internet?Why a Local Internet?

Overcome distance limitationsOvercome distance limitations 10Base-T networks span only 500 meters10Base-T networks span only 500 meters

Overcome congestion and latency Overcome congestion and latency Individual shared media networks running around 10 Individual shared media networks running around 10

Mbps become saturated at 200-300 stations.Mbps become saturated at 200-300 stations.

Connect dissimilar LANsConnect dissimilar LANs Link Ethernet and Token-Ring Network LANsLink Ethernet and Token-Ring Network LANs

55

Local Internetting to Increase Distance SpansLocal Internetting to Increase Distance Spans

10Base-T LAN inHeadquarters Building

(500 m maximum distance)

10Base-T LAN inFactory Building

(500 m maximum distance)

Transmission Link(no max distance)

InternettingDevice

InternettingDevice

HQ LANHQ LANHQ LANHQ LAN

Factory LANFactory LANFactory LANFactory LAN

66

A Congested Shared Media LANA Congested Shared Media LAN

AA BB CC DDStations Stations

Department 1:150 Stations

Department 2:150 Stations

B transmits to AAll stations in Department 2

hear the message

Before: Single LAN

Each station hears the traffic of 300 stations:Heavily congested.

77

Internetting keep most traffic within LANsInternetting keep most traffic within LANs

AA BB CC DDStations Stations

Department 1:150 Stations

Department 2:150 Stations

B transmits to AInternetting Device

Blocks the Transmission of this messageto Department 2

InternettingDevice

Traffic of 150 stations:Not Congested

After Resegmentation

Traffic of 150 stations:Not Congested

88

Internetting Devices: BridgesInternetting Devices: Bridges

Simple, automatic, inexpensive, fastSimple, automatic, inexpensive, fast

Usually only two portsUsually only two ports

A fast, cost-effective choice for small internetsA fast, cost-effective choice for small internets

See See CISCO CISCO whitepaper for more detailswhitepaper for more details

99

Multiple BridgesMultiple Bridges

LAN 1LAN 1

LAN 2LAN 2

LAN 3LAN 3

LAN 5LAN 5LAN 4LAN 4

X

No Loops AllowedProblematic for large bridged internets

No Loops AllowedProblematic for large bridged internets

1010

Multiple BridgesMultiple Bridges

LAN 1LAN 1

LAN 2LAN 2

LAN 3LAN 3

LAN 5LAN 5No loops means only one path between LANsNo alternative routing if failures, congestionNo way to optimize routing for security, etc.

No loops means only one path between LANsNo alternative routing if failures, congestionNo way to optimize routing for security, etc.

Route BetweenLANs 1, 5

XX

1111

LAN 1LAN 1

LAN 2LAN 2

LAN 3LAN 3

LAN 5LAN 5

Allows backup linksDisabled during normal operationIf a failure occurs, automatically initiated

Allows backup linksDisabled during normal operationIf a failure occurs, automatically initiated

Route BetweenLANs 1, 5

802.1 Spanning Tree Standard802.1 Spanning Tree Standard

BackupBackupLinkLink

1212

Bridging LANs with Different Physical and MAC LayersBridging LANs with Different Physical and MAC Layers

802.3 10Base-TEthernet LAN

802.5Token-Ring Network

Hub

10Base-TConnection

802.5Connection

Bridge

1313

Bridging LANs with Different Physical and MAC LayersBridging LANs with Different Physical and MAC Layers

802.2LLC Standard LLC Layer (Same)LLC Layer (Same)

802.2 LLC Standard

802.1Bridging Standard

Bridging Layer(Same)

Bridging Layer(Same)

802.1Bridging Standard

802.3 MAC Layer(CSMA/CD)

MAC Layer(Different)

MAC Layer(Different)

802.5 MAC Layer(Token-Passing)

10Base-T Connectionto Hub

Physical Layer(Different)

Physical Layer(Different)

802.5 Connectionto Access Unit

1414

Problems of BridgesProblems of Bridges

Do Not Stop Broadcast MessagesDo Not Stop Broadcast Messages Servers broadcast their existence about twice a Servers broadcast their existence about twice a

minuteminute

In contrast to normal messages, which are designed In contrast to normal messages, which are designed to go to single stations, broadcast messages go to all to go to single stations, broadcast messages go to all stations.stations.

Goes to all stations on the network; bridges pass Goes to all stations on the network; bridges pass these messages onthese messages on

Problematic in large bridged intranetsProblematic in large bridged intranets

1515

Problems of BridgesProblems of Bridges

Do Not Stop Any Client from Logging into Do Not Stop Any Client from Logging into Any ServerAny Server Poor security. Only password protection on Poor security. Only password protection on

serversservers

Bad if servers hold grades in a universityBad if servers hold grades in a university

Bad for departmental servers holding key Bad for departmental servers holding key personnel or financial data in a firmpersonnel or financial data in a firm

1616

Switches Solve Bridge ProblemsSwitches Solve Bridge Problems

Begin as Multiport BridgesBegin as Multiport Bridges Add broadcast reduction, securityAdd broadcast reduction, security

1717

Simple Switched InternetSimple Switched Internet

LAN ALAN A

LAN BLAN B

LAN CLAN C

LAN DLAN D

Connection 1

Connection 1

Connection 2Connection 2

Switches can carrymessages betweenseveral pairs of LANssimultaneously.

Switches can carrymessages betweenseveral pairs of LANssimultaneously.

No Waiting!

1818

Switched Internet with Multiple Switches Switched Internet with Multiple Switches

Switches are arranged in a hierarchyOnly one route between any two LANsNo routing around failure, congestionNo optimization of routes

Switch A

Switch B Switch C

Switch D

Route: 1-B-A-C-2

LAN 1LAN 1LAN 2LAN 2

1919

Switch HierarchySwitch Hierarchy

Switches can be Switches can be arranged hierarchicallyarranged hierarchically

Levels of SwitchesLevels of Switches Desktop switches (only a few MAC addresses Desktop switches (only a few MAC addresses

can be supported)can be supported)

Workgroup switches (MAC addresses for Workgroup switches (MAC addresses for members of a department)members of a department)

Enterprise switches (large number of MAC Enterprise switches (large number of MAC addresses)addresses)

2020

Virtual LANs Reduce BroadcastingVirtual LANs Reduce Broadcasting

Stations are Stations are Divided into GroupsDivided into Groups Called Virtual LANs (VLANs)Called Virtual LANs (VLANs) Server, other broadcasts limited to VLANsServer, other broadcasts limited to VLANs Not to all stations on all portsNot to all stations on all ports

LAN ALAN A LAN BLAN B LAN CLAN C LAN DLAN D

Server only broadcasts to its VLAN stations on LAN A, LAN CServer only broadcasts to its VLAN stations on LAN A, LAN C

2121

VLANs Add SecurityVLANs Add Security

Only stations on the same VLAN as a Only stations on the same VLAN as a server can reach it to log inserver can reach it to log in

LAN ALAN A LAN BLAN B LAN CLAN C LAN DLAN D

Client can only reach server if they are on the same VLANClient can only reach server if they are on the same VLAN

On VLAN 7On VLAN 7 On VLAN 36On VLAN 36

XX

2222

Simple Local Internet Using Ethernet Switching and 10Base-TSimple Local Internet Using Ethernet Switching and 10Base-T

Ethernet Switch

10Base-T Hub

10Base-T Hub 10Base-T Hub

In a switched Ethernetinternet:Stations connect to hubs.Hubs connect to switches.

LANLANLANLAN

2323

Switched InternetsSwitched Internets

The Move Toward Switched NetworksThe Move Toward Switched Networks

All-switched LANs with stations connected to switches All-switched LANs with stations connected to switches are still too expensive for most firms. Need a port for are still too expensive for most firms. Need a port for each station.each station.

Using switches as internetting devices is cost-effective Using switches as internetting devices is cost-effective today. Only hubs connect to switches. Only need a today. Only hubs connect to switches. Only need a port for each hubport for each hub

As switching costs fall, companies can later move As switching costs fall, companies can later move switching down to individual LANs by replacing hubs switching down to individual LANs by replacing hubs by switches. See CISCO white paper for details.by switches. See CISCO white paper for details.

2424

RoutersRouters

Most sophisticated internetting devicesMost sophisticated internetting devices Provide services for linking Provide services for linking thousands of subnetsthousands of subnets

Used in the worldwide Internet, also within firmsUsed in the worldwide Internet, also within firms

Efficient for long-distance transmissionEfficient for long-distance transmission

Provide wide range of management services to Provide wide range of management services to give relatively automatic operationgive relatively automatic operation

By far the By far the most expensive internetting devicesmost expensive internetting devices

2525

RouteRoute

End-to-End ConnectionEnd-to-End Connection

LAN ALAN A

LAN DLAN D

LAN BLAN B

11

2233

44

55LAN A - 1 - 3 - 5 - LAN DLAN A - 1 - 3 - 5 - LAN D

2626

Alternative RoutesAlternative Routes

Multiple Ways to Get from LAN A to LAN DMultiple Ways to Get from LAN A to LAN D

LAN ALAN A

LAN DLAN D

LAN BLAN B

11

2233

44

55

A-1-3-5-DA-1-3-5-DA-1-3-4-DA-1-3-4-DA-2-5-DA-2-5-DEtc.Etc.

2727

Advantages of Alternative RoutingAdvantages of Alternative Routing

Routing Around FailuresRouting Around Failures Failed switches, trunk lines connecting switchesFailed switches, trunk lines connecting switches

Routing Around CongestionRouting Around Congestion More common than outright failuresMore common than outright failures

Route OptimizationRoute Optimization Least cost routeLeast cost route Most reliable routeMost reliable route Most secure route, etc.Most secure route, etc.

2828

Mixing Switches and RoutersMixing Switches and Routers

Site A

Router

Switch

Switch

Site C

Site B

LANLAN

LANLAN

LANLANLANLAN

Router

Router

2929

Distributed Backbone NetworkDistributed Backbone Network

RouterRouter Router

FDDI Backbone RingLAN 1LAN 1LAN 2LAN 2

LAN 3LAN 3

3030

Backbone NetworkBackbone Network

Network that Links SubnetsNetwork that Links Subnets Subnets take the place of stationsSubnets take the place of stations

Distributed BackboneDistributed Backbone Backbone runs past all stationsBackbone runs past all stations

If a single router (or other internettingIf a single router (or other internetting device) device) fails, only that station is disconnectedfails, only that station is disconnected

FDDI is popular because of its possible 200 km FDDI is popular because of its possible 200 km circumference, 100 Mbps speedscircumference, 100 Mbps speeds

3131

Local Internet Using Collapsed BackboneLocal Internet Using Collapsed Backbone

LAN ALAN A LAN BLAN B LAN CLAN C

Routersat LANs

Routersat LANs

Central Switch or Router

3232

Collapsed BackboneCollapsed Backbone

Single point of maintenanceSingle point of maintenance Easy to maintain the networkEasy to maintain the network

Single point of failureSingle point of failure If the central device fails, serious problemsIf the central device fails, serious problems

Types of central devicesTypes of central devices SwitchesSwitches RoutersRouters

3333

OSI LayersOSI Layers

Layer 1 (Physical)Layer 1 (Physical) Electrical signaling over a physical linkElectrical signaling over a physical link

Layer 2 (Data Link)Layer 2 (Data Link) Data framing and administration of communication over a single data linkData framing and administration of communication over a single data link

Point to point connectionPoint to point connection

Shared media LAN with only one possible path between two stationShared media LAN with only one possible path between two station

Layer 3 (Network)Layer 3 (Network) Routing across an internet with multiple alternative routesRouting across an internet with multiple alternative routes

Or a subnet that offers alternative routes, but these rarely existOr a subnet that offers alternative routes, but these rarely exist

3434

Internetting DevicesInternetting Devices

HubsHubs Layer 1: merely reflect bits back outLayer 1: merely reflect bits back out

Bridges, SwitchesBridges, Switches Layer 2: Work with MAC addressesLayer 2: Work with MAC addresses No alternative routingNo alternative routing

RoutersRouters Layer 3: routing across internetLayer 3: routing across internet Only device with alternative routingOnly device with alternative routing

3535

TCP/IP InternettingTCP/IP Internetting

Subnet layerSubnet layer Links stations on same subnetLinks stations on same subnet

Often IEEE LAN standardsOften IEEE LAN standards

PPP for telephone connectionsPPP for telephone connections

TCP/IP specifies almost any subnet standardTCP/IP specifies almost any subnet standard

For LANs, etc., specifies OSIFor LANs, etc., specifies OSI

OSI further subdivides into Physical, Data LinkOSI further subdivides into Physical, Data Link

ApplicationApplication

TransportTransport

InternetInternet

SubnetSubnetData LinkData Link

PhysicalPhysical

TCP/IPTCP/IP OSIOSI

3636

TCP/IP InternettingTCP/IP Internetting

Internet layer:Internet layer: Links stations across internetsLinks stations across internets

Main standard is the Internet Protocol (IP)Main standard is the Internet Protocol (IP)

Dominant protocol for routersDominant protocol for routers

ApplicationApplication

TransportTransport

InternetInternet

SubnetSubnet

3737

TCP/IP InternettingTCP/IP Internetting

Transport layer:Transport layer: Links computers, even if different platformsLinks computers, even if different platforms

Main standards are Transmission Control Protocol Main standards are Transmission Control Protocol (TCP) and User Datagram Protocol (UDP)(TCP) and User Datagram Protocol (UDP)

Application layer:Application layer: Links application programs even if from different Links application programs even if from different

vendorsvendors

Many standards, because many applicationsMany standards, because many applications

SMTP for e-mail; HTTP for the WWW, etcSMTP for e-mail; HTTP for the WWW, etc..

ApplicationApplication

TransportTransport

InternetInternet

SubnetSubnet

3838

Universal AddressingUniversal Addressing

Each host has a unique IP NumberEach host has a unique IP Number 32-bit binary number32-bit binary number

Goes in the IP header’s source and destination fieldsGoes in the IP header’s source and destination fields

1000000010101011000100010000110110000000101010110001000100001101

Impossible to rememberImpossible to remember

DestinationDestinationSourceSource

IP PacketIP Packet 4 Bytes4 Bytes 4 Bytes4 Bytes

3939

Subnet MaskSubnet Mask

Problem: IP numbers do not include subnettingProblem: IP numbers do not include subnetting

Solution: Create a second number: a Subnet MaskSolution: Create a second number: a Subnet Mask

Define which bits of the IP address refer to subnets Define which bits of the IP address refer to subnets vs. hosts on subnetvs. hosts on subnet

Subnet mask is 32 bits long, in dot quad formatSubnet mask is 32 bits long, in dot quad format

See last meeting See last meeting TCP/IP in NTTCP/IP in NT for basic IP and for basic IP and Subnet Mask concepts.Subnet Mask concepts.

4040

RoutersRouters

Routers also get IP addressesRouters also get IP addresses So packets can be sent to them for routingSo packets can be sent to them for routing Has network ID of the network on which it sitsHas network ID of the network on which it sits Must be assigned a host IDMust be assigned a host ID Example: 128.171.17.1Example: 128.171.17.1

DefaultRouter

IP Packetfor Delivery

Another Router

128.171.17.1128.171.17.1

128.171.17.104128.171.17.104

4141

RoutersRouters

Subnets can have Multiple RoutersSubnets can have Multiple Routers There is usually a default router for packet deliveryThere is usually a default router for packet delivery Default router is used if no router is specifiedDefault router is used if no router is specified Routers are sometimes called gateways in TCP/IPRouters are sometimes called gateways in TCP/IP

DefaultRouter

IP Packetfor Delivery

Other Router

4242

Routing Protocols

There are no “master” routers.

Each router works independently to do routing.

This requires each router to build a “routing table” thatcontains information about the locations of other routers.

There are no “master” routers.

Each router works independently to do routing.

This requires each router to build a “routing table” thatcontains information about the locations of other routers.

RoutingTable

RoutingTable

4343

Routing Protocols

Routing protocols allowrouters to exchangeinformation in theirrouting tables.

Routing protocols allowrouters to exchangeinformation in theirrouting tables.

RoutingTable

RoutingTable

4444

Peer Control Among RoutersPeer Control Among Routers

Routers Communicate Among ThemselvesRouters Communicate Among Themselves To coordinate their actions without central controlTo coordinate their actions without central control Share knowledge of network connectivityShare knowledge of network connectivity Common standards are RIP, OSPF, BGPCommon standards are RIP, OSPF, BGP

RouterCoordination

Message

4545

Routing ProtocolsRouting Protocols

RIP - RIP - RouterRouter Information Protocol Information Protocol High overhead, but simple and OK for small networksHigh overhead, but simple and OK for small networks

OSPF - OSPF - Open Open ShortestShortest Path First Path First Optimizes routing, but complexOptimizes routing, but complex

BGP - BGP - Border Gateway (Router) ProtocolBorder Gateway (Router) Protocol Used in Internet Backbone RoutersUsed in Internet Backbone Routers

Read Read Cisco Cisco whitepaper for more on routingwhitepaper for more on routing

4646

Autonomous Systems

AutonomousRouter

Border Router

RIPor

OSPF

RIPor

OSPF

BPG

Border Router

Organization can select anyrouting protocol to synchronizeits autonomous (internal)routers. RIP and OSPF arecommon.

Border routers that linkautonomous systems normallyuse BPG.

Autonomous System

4747

Error HandlingError Handling

TCP/IP a comprehensive set of error TCP/IP a comprehensive set of error handling processeshandling processes The Internet Control Message Protocol (ICMP) is used The Internet Control Message Protocol (ICMP) is used

to send error messages.to send error messages.

Hosts, Routers send ICMP messages to one another if a Hosts, Routers send ICMP messages to one another if a problem occursproblem occurs

““Host not found” is a common ICMP error message.Host not found” is a common ICMP error message.

Host

Router

ICMP Error Message

4848

Internet Control Message Protocol (ICMP)

The Internet Control Message Protocol (ICMP)is for delivering supervisory messagesamong hosts and routers

The Internet Control Message Protocol (ICMP)is for delivering supervisory messagesamong hosts and routers

4949

Internet Control Message Protocol (ICMP)

“Host Unreachable”

Error MessagesError Messages

5050

Internet Control Message Protocol (ICMP)

SourceQuench

Flow Control

“Source Quench” tells hostto reduce transmission rate.

Flow Control

“Source Quench” tells hostto reduce transmission rate.

5151

Internet Control Message Protocol (ICMP)

“EchoRequest”

“EchoResponse”

Source host can ask questions of destination hosts.

“Echo Request” asks if the other hostis reachable.

Destination host sends back “Echo Response.”

Usually implemented with “Ping”program.

Source host can ask questions of destination hosts.

“Echo Request” asks if the other hostis reachable.

Destination host sends back “Echo Response.”

Usually implemented with “Ping”program.

5252

AutoconfigurationAutoconfiguration

Autoconfiguration Server has a bank of addressesAutoconfiguration Server has a bank of addresses When a PC “logs in,” it gets a temporary IP numberWhen a PC “logs in,” it gets a temporary IP number..

Popular standards are DHCP (in Windows NT) and RARPPopular standards are DHCP (in Windows NT) and RARP

Large stations receive permanent addressesLarge stations receive permanent addresses

DHCP Request for Address

DHCP Response:Your Temporary Address is

127.171.17.35

DHCPServer

5353

Autoconfiguration Protocol

SourceHost

Auto-Configuration

Host

Source host sends Autoconfigutation RequestMessage to the autoconfiguration host

“My 48-bit MAC subnet address is X.Please give me a 32-bit IP host address.”

Autoconfiguration Request Message

5454

Autoconfiguration Protocol

SourceHost

Auto-Configuration

Host

Autoconfiguration host sends back aAutoconfiguration response message.

“Computer at MAC Address X,your 32-bit IP host number is ‘110100…’.”

Autoconfiguration Response Message

5555

Autoconfiguration ProtocolsAutoconfiguration Protocols

RARP: Reverse Address Resolution ProtocolRARP: Reverse Address Resolution Protocol Older autoconfiguration protocolOlder autoconfiguration protocol

BootpBootp Another older protocolAnother older protocol

DHCPDHCP Dynamic Host Configuration ProtocolDynamic Host Configuration Protocol

Built into Windows NT ServerBuilt into Windows NT Server

5656

Domain Name ServiceDomain Name Service

Hosts also have IP host namesHosts also have IP host names Voyager.cba.hawaii.eduVoyager.cba.hawaii.edu

Like nicknamesLike nicknames

IP packets require formal IP numbers to put in their source IP packets require formal IP numbers to put in their source and destination fieldsand destination fields

If tell your software the IP host name, it must look up the If tell your software the IP host name, it must look up the IP numberIP number

5757

Domain Name ServiceDomain Name Service

Program knowing a host name sends request Program knowing a host name sends request to Domain Name Service (DNS) Server; to Domain Name Service (DNS) Server; receives IP Numberreceives IP Number

DNS Request forVoyager.cba.hawaii.edu

DNS Response: 128.171.17.13

DNSServer

5858

Domain Name System (DNS)

SourceHost

DNSHostDNS Request Message

Source host sends DNS Request Message to DNS host.“I need the 32-bit IP host number for the host namedvoyager.cba.hawaii.edu.”

Source host sends DNS Request Message to DNS host.“I need the 32-bit IP host number for the host namedvoyager.cba.hawaii.edu.”

5959

Domain Name System (DNS)

SourceHost

DNSHost

DNSHost

DNS Response Message

DNS host returns a DNS Reply Message.“The 32-bit host number is 128.171.44.53”.

DNS host returns a DNS Reply Message.“The 32-bit host number is 128.171.44.53”.

6060

Domain Name System (DNS)

SourceHost

DNSHost

DNSHost

Each network has a DNS host May also have a secondary DNS host Network DNS host may only know theIP names and numbers of local hosts onthe network For other IP names, contacts anotherDNS host, especially root DNS hosts,which should have extensive information

Each network has a DNS host May also have a secondary DNS host Network DNS host may only know theIP names and numbers of local hosts onthe network For other IP names, contacts anotherDNS host, especially root DNS hosts,which should have extensive information

6161

Total Length (in Bytes)Total Length (in Bytes)

Fragment OffsetFragment Offset

Header ChecksumHeader Checksum

Internet Protocol PacketInternet Protocol Packet

Source AddressSource Address

Destination AddressDestination Address

Options Plus PaddingOptions Plus Padding

DataData

Version IHL Type of Service

Identifier Flags

Time to Live Protocol

Current version isVersion 4.

A new version,Version 6,is coming.

6262

Total Length (in Bytes)Total Length (in Bytes)

Fragment OffsetFragment Offset

Header ChecksumHeader Checksum

Internet Protocol PacketInternet Protocol Packet

Version IHL Type of Service

Identifier Flags

Time to Live Protocol

There is only error checking for the header,not for the entire packet.

If an error is detected in the header,the packet is discarded

There is only error checking for the header,not for the entire packet.

If an error is detected in the header,the packet is discarded

6363

Total Length (in Bytes)Total Length (in Bytes)

Fragment OffsetFragment Offset

Header ChecksumHeader Checksum

Internet Protocol PacketInternet Protocol Packet

Source Address (32 bits)Source Address (32 bits)

Destination Address (32 bits)Destination Address (32 bits)

Options Plus PaddingOptions Plus Padding

DataData

Version 4 addresses only have 32 bits.Not enough for the number of Internet hosts.

Will be raised to 128 bits in Version 6

Version 4 addresses only have 32 bits.Not enough for the number of Internet hosts.

Will be raised to 128 bits in Version 6