internet protocol (ip)jain/cis678-97/ftp/f14_ipa.pdf · the ohio state university raj jain 14-18 ip...
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Raj JainThe Ohio State University
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Internet ProtocolInternet ProtocolInternet ProtocolInternet ProtocolInternet ProtocolInternet Protocol(IP)(IP)(IP)(IP)(IP)(IP)
Raj JainThe Ohio State University
Columbus, OH [email protected]
http://www.cis.ohio-state.edu/~jain/
Raj JainThe Ohio State University
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❑ Internetworking
❑ IP Address format
❑ IP data forwarding
❑ Fragmentation and reassembly
Ref: Chapters 13, 14, 16, and 17 of Comer’s ComputerNetworks and Internets
Overview
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InternetworkingInternetworkingInternetworking
❑ Internetwork = Collection of networksConnected via routers
Fig 13.1
Network NetworkRouter
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Internet = Virtual NetworkInternet = Virtual NetworkInternet = Virtual Network❑ Any computer can talk to any other computer
Fig 13.3
Net 2Net 1 Net 3
Net 4
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IP AddressIP AddressIP Address
❑ Class A: Network Local071 24 bits
Network Local10142 16 bits
❑ Class B:
Network Local110213 8 bits
❑ Class C:
❑ Local = Subnet + Host (Variable length)
Router Router
Subnet
Host Group (Multicast)1110284 bits
❑ Class D:
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Computing The Class of an AddressComputing The Class of an AddressComputing The Class of an Address
First 4 bits Index Class0000 0 A0001 1 A0010 2 A0011 3 A0100 4 A0101 5 A0110 6 A0111 7 A1000 8 B1001 9 B1010 10 B1011 11 B1100 12 C1101 13 C1110 14 D1111 15 E
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Classes and Dotted Decimal NotationClasses and Dotted Decimal NotationClasses and Dotted Decimal Notation
❑ Binary: 11000000 00000101 00110000 00000011Hex Colon: C0:05:30:03Dotted Decimal: 192.5.48.3
Fig 14.4
Class RangeA 0 through 127B 128 through 191C 192 through 223D 224 through 239E 240 through 255
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Division of the Address SpaceDivision of the Address SpaceDivision of the Address Space
❑ Not all possible addresses can be used.
Fig 14.5
Class Bits inPrefix
Max # ofNets
Bits inSuffix
Max # of Hostsper Net
A 7 128 24 16,777,216B 14 16,384 16 65,536C 21 2,097,152 8 256
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An Addressing ExampleAn Addressing ExampleAn Addressing Example
❑ All hosts on a network have the same network prefix
Fig 14.6
128.10
192.5.48
128.10.0.1
Router
Router
128.211
10 Router
128.10.0.2 128.211.6.115
192.5.48.310.0.0.37 10.0.0.49
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Multi-Homed HostsMulti-Homed HostsMulti-Homed Hosts
❑ Each interface has an address.Two or more interfaces ⇒ Multi-homed hosts
❑ Multihoming is for reliability or performance
HostR1
Interfaces
R2
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Routers and the IP Addressing PrincipleRouters and the IP Addressing PrincipleRouters and the IP Addressing Principle
❑ Routers have two or more addresses.One for each interface.
Fig 14.8
WAN 78.0.0.0
Token Ring223.240.129.0
Router
Router
Ethernet131.108.0.0
131.108.99.5
223.24.129.2
223.240.129.17
78.0.0.17
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❑ All-0 host suffix ⇒ Network Address
❑ All-0s ⇒ This computer
❑ All-1 host suffix ⇒ All hosts on the destination net(directed broadcast),All-0 host suffix ⇒ Berkeley directed broadcast address
❑ All-1s ⇒ All hosts on this net (limited broadcast)
❑ 127.*.*.* ⇒ Looback through IP layer
Special IP AddressesSpecial IP AddressesSpecial IP Addresses
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HomeworkHomeworkHomework
❑ Read chapters 13, 14
❑ Submit answer to exercise 14.8(requires 14.6 and 14.7 also)
❑ Use your program to printout characteristics of thefollowing addresses using a subnet mask of255.255.255.0: 164.107.61.200, 164.107.61.0,164.107.61.255, 127.107.61.200, 0.0.0.0
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IP FeaturesIP FeaturesIP Features
❑ Connectionless service
❑ Variable size datagrams
❑ Best-effort delivery: Delay, out-of-order, corruption,and loss possible. Higher layers should handle these.
❑ Handles only data forwardingUses routing tables prepared by other protocols, e.g.,Open Shortest Path First (OSPF),Routing Information Protocol (RIP)
❑ Provides only “Send” and “Delivery” servicesError and control messages generated byInternet Control Message Protocol (ICMP)
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Forwarding an IP DatagramForwarding an IP DatagramForwarding an IP Datagram❑ Delivers datagrams to destination network (subnet)
❑ Routers maintain a “routing table” of “next hops”
❑ Next Hop field does not appear in the datagram
Table at R2:
Fig 16.2
Net 1 Forward to R1Net 2 Deliver DirectNet 3 Deliver DirectNet 4 Forward to R3
Net 1 R1 Net 2 R2 Net 3 R3 Net 4
Destination Next Hop
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IP Addresses and Routing Table EntriesIP Addresses and Routing Table EntriesIP Addresses and Routing Table Entries❑ IF ((Mask[i] & Destination Addr) = = Destination[i])
Forward to NextHop[i]
Destination Mask Next Hop30.0.0.0 255.0.0.0 40.0.0.740.0.0.0 255.0.0.0 Deliver direct
128.1.0.0 255.255.0.0 Deliver direct192.4.10.0 255.255.255.0 128.1.0.9
30.0.0.0 40.0.0.0 128.1.0.0 192.4.0.0
30.0.0.7
40.0.0.7 128.1.0.8 192.4.10.9
40.0.0.8 128.1.0.9
Fig 16.3
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IP Datagram FormatIP Datagram FormatIP Datagram Format
Vers H. Len Service Type Total LengthIdentification Flags
Time to live Type Header ChecksumFragment Offset
Source IP AddressDestination IP Address
IP Options (May be omitted) Padding
Data
Fig 16.4
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IP FormatIP FormatIP Format
❑ Version (4 bits)
❑ Internet header length (4 bits): in 32-bit words.Min header is 5 words or 20 bytes.
❑ Type of service (8 bits): Reliability, precedence,delay, and throughput
❑ Total length (16 bits): header + data in bytesTotal must be less than 64 kB.
❑ Identifier (16 bits): Helps uniquely identify thedatagram during its life for a given source, destinationaddress
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IP Header (Cont)IP Header (Cont)IP Header (Cont)
❑ Flags (3 bits): More flag - used for fragmentationNo-fragmentationReserved
❑ Fragment offset (13 bits): In units of 8 bytes
❑ Time to live (8 bits): Specified in router hops
❑ Protocol (8 bits): Next level protocol to receive thedata
❑ Header checksum (16 bits): 1’s complement sum ofall 16-bit words in the header
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IP Header (Cont)IP Header (Cont)IP Header (Cont)
❑ Source Address (32 bits): Original source. Does not change along the path.
❑ Destination Address (32 bits): Final destination.Does not change along the path.
❑ Options (variable): Security, source route, recordroute, stream id (used for voice) for reservedresources, timestamp recording
❑ Padding (variable):Makes header length a multiple of 4
❑ Data (variable): Data + header < 65,535 bytes
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Transmission Across An InternetTransmission Across An InternetTransmission Across An Internet
❑ Datalink header changes at every hopFig 17.2
Datalink header
IP header
D
S Datagram
Datagram
Datagram
Datagram
Datagram
Datagram
Datagram
Header 1
Header 2
Header 3
Source
Destination
Net 1
Net 2
Net 3
R1
R2
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Maximum Transmission UnitMaximum Transmission UnitMaximum Transmission Unit
❑ Each subnet has a maximum frame sizeEthernet: 1518 bytesFDDI: 4500 bytesToken Ring: 2 to 4 kB
❑ Transmission Unit = IP datagram (data + header)
❑ Each subnet has a maximum IP datagram length: MTU
Fig 17.3
S RNet 1
MTU=1500Net 2
MTU=1000R
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IP Protocol NumbersIP Protocol NumbersIP Protocol Numbers
Decimal Key word Protocol0 Reserved1 ICMP Internet Control Message Protocol2 IGMP Internet Group Management
Protocol4 ST Stream Protocol5 TCP Transmission Control Protocol8 EGP Exterior Gateway Protocol9 IGP Interior Gateway Protocol17 UDP User Datagram Protocol
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IP Options CodingIP Options CodingIP Options Coding
❑ Flag Copy: 0 = Copy the option only into the firstfragment of a fragmented datagram1 = Copy into all fragments
❑ Class: 0 =User or control, 1=Reserved,2=Diagnostics, 3=reserved
Type Length Value
Flag Copy Class Number
1B 1B nB
1b 2b 5b
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IP OptionsIP OptionsIP OptionsClass Number Length Description0 0 0 End of Options0 1 0 No Op0 2 11 Security0 3 Var Loose Source Routing0 7 Var Record Route0 8 4 Stream ID (obsolete)0 9 Var Strict Source Routing
4 Var Internet Time-Stamp2
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IP Source RoutingIP Source RoutingIP Source Routing
Code Length Pointer Router Data
P 128.2.3.4 128.7.8.9 128.10.4.12
P 128.2.3.4 128.7.8.9 128.10.4.12
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Route RecordingRoute RecordingRoute Recording
Code Length Pointer Route Data
P 128.2.3.4 Empty Empty
P 128.2.3.4 128.7.8.9 Empty
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Timestamp OptionTimestamp OptionTimestamp Option
Code Length Pointer Data
Oflw Flags IP Address 1 Timestamp 1
IP Address n Timestamp n
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FragmentationFragmentationFragmentation❑ Datagrams larger than MTU are fragmented
❑ Original header is copied to each fragment and thenmodified (fragment flag, fragment offset, length,...)
Fig 17.4
IP Header Original Datagram
IP Hdr 1 Data 1 IP Hdr 3 Data 3IP Hdr 2 Data 2
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FragmentationFragmentationFragmentation
ID = 12345, More = 1Offset = 0W, Len = 256B
ID = 12345, More = 1Offset = 160W, Len = 1500B
ID = 12345, More = 1Offset = 32W, Len = 256B
ID = 12345, More = 1Offset = 64W, Len = 256B
ID = 12345, More = 1Offset = 96W, Len = 256B
ID = 12345, More = 1Offset = 128W, Len = 256B
ID = 12345, More = 1Offset = 160W, Len = 220B
ID = 12345, More = 1Offset = 0W, Len = 512B
ID = 12345, More = 1Offset = 64W, Len = 512B
ID = 12345, More = 1Offset = 128W, Len = 476B
MTU = 256BMTU = 1500B MTU = 512B
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ReassemblyReassemblyReassembly
Fig 17.5
❑ Reassambly only at the final destination
❑ Partial datagrams are discarded after a timeout
❑ Fragments can be further fragmented along the path.Subfragments have a format similar to fragments.It is not possible to tell how many times fragmented.
❑ Minimum MTU along a path ⇒ Path MTU
Net 1MTU=1500
Net 3MTU=1500
R2
S D
Net 2MTU=1000
R1
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SummarySummarySummary
❑ IPv4 uses 32-bit addresses organized as networkprefix and host suffix.
❑ Four classes of networks: A, B, C, D
❑ Routers determine next hop using routing tables
❑ IP provides connectionless unreliable service
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HomeworkHomeworkHomework
❑ Read Chapters 16, 17
❑ Submit answers to exercises 16.7, 17.4