Download - Local Internets
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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
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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
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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
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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
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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.
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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
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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
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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
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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
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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
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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
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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
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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
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Switches Solve Bridge ProblemsSwitches Solve Bridge Problems
Begin as Multiport BridgesBegin as Multiport Bridges Add broadcast reduction, securityAdd broadcast reduction, security
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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!
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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
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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)
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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
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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
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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
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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.
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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
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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
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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.
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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.
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Mixing Switches and RoutersMixing Switches and Routers
Site A
Router
Switch
Switch
Site C
Site B
LANLAN
LANLAN
LANLANLANLAN
Router
Router
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Distributed Backbone NetworkDistributed Backbone Network
RouterRouter Router
FDDI Backbone RingLAN 1LAN 1LAN 2LAN 2
LAN 3LAN 3
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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.
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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
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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
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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
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Routing Protocols
Routing protocols allowrouters to exchangeinformation in theirrouting tables.
Routing protocols allowrouters to exchangeinformation in theirrouting tables.
RoutingTable
RoutingTable
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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
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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
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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
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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
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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
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Internet Control Message Protocol (ICMP)
SourceQuench
Flow Control
“Source Quench” tells hostto reduce transmission rate.
Flow Control
“Source Quench” tells hostto reduce transmission rate.
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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.
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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
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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
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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
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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
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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
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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
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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.”
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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”.
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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
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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.
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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
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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