1. Module A Panko and Panko Business Data Networks and Telecommunications, 8 th Edition © 2011 Pearson Education, Inc. Publishing as Prentice Hall

2.  This module presents additional material about TCP/IP standards.  Most of the material in this module can be read after Chapter 2, but some of it is designed to be covered after Chapter 10.  The material in this module is not designed to be read front-to-back like a regular chapter, although it can be covered this way. 2 © 2011 Pearson Education, Inc. Publishing as Prentice Hall

3. Multiplexing Details of TCP operationIP mask operationsIP Version 6IP fragmentationDynamic routing protocolsAddress Resolution ProtocolIP Address ClassesMobile IP 3 © 2011 Pearson Education, Inc. Publishing as Prentice Hall

4.  IP packets can carry different things in their data fields. ◦ TCP segments ◦ UDP datagrams ◦ ICMP supervisory messages (later) ◦ RIP messages (later) 4 IP Data FieldIP Header © 2011 Pearson Education, Inc. Publishing as Prentice Hall

5.  We say that IP can multiplex (mix) different types of traffic in a stream of IP packets. 5 UDPIP-HTCPIP-HUDPIP-HICMPIP-H Stream of Arriving or Outgoing IP Packets Single IP Packet Carrying UDP Datagram © 2011 Pearson Education, Inc. Publishing as Prentice Hall

6.  The IP process must pass contents of arriving IP packets to the correct process for subsequent handling. 6 IP TCPUDP ICMP UDPIP-H IP Process Arriving Packets © 2011 Pearson Education, Inc. Publishing as Prentice Hall

7.  IP process must also accept messages from multiple processes and multiplex them on an outgoing stream. 7 IP TCPUDP ICMP UDPIP-H IP Process Outgoing Packets © 2011 Pearson Education, Inc. Publishing as Prentice Hall

8.  Need a way for receiving IP process to know what is in the data field ◦ So it can pass the contents to the appropriate process 8 IP Data FieldIP Header © 2011 Pearson Education, Inc. Publishing as Prentice Hall

9.  IP Header has an 8-bit Protocol field. ◦ Identifies the contents of the data field  1=ICMP, 8=TCP, 17=UDP, and so on 9 Total Length in Bytes (16) Time to Live (8) Version (4) Hdr Len (4) TOS (8) Indication (16 bits)Flags (3)Fragment Offset (13) Source IP Address Destination IP Address Header Checksum (16) Protocol (8 ) © 2011 Pearson Education, Inc. Publishing as Prentice Hall

10.  Other Messages Have Analogous Fields ◦ Identify contents of data field  TCP and UDP ◦ Have Port number fields ◦ Identify the application process (80=HTTP) 10 Source Port # (16)Destination Port # (16) Sequence Number (32 bits) Acknowledgement Number (32 bits) Hdr Len (4) Flags (6)Window Size (16)Reserved (6) © 2011 Pearson Education, Inc. Publishing as Prentice Hall

11.  Other Messages Have Analogous Fields ◦ Identify contents of data field  PPP ◦ Protocol field identifies contents of information field as IP, IPX, a supervisory message, and so on. 11 FlagAddrCtrlProtInfoCRCFlag © 2011 Pearson Education, Inc. Publishing as Prentice Hall

12. Multiplexing Details of TCP operation IP mask operationsIP Version 6IP fragmentationDynamic routing protocolsAddress Resolution ProtocolIP Address ClassesMobile IP 12 © 2011 Pearson Education, Inc. Publishing as Prentice Hall

13.  TCP is Reliable. ◦ IP packets carrying TCP segments may arrive out of order. ◦ TCP must put the TCP segments in order. 13 34215 © 2011 Pearson Education, Inc. Publishing as Prentice Hall

14.  TCP is Reliable. ◦ Each correct TCP segment is acknowledged by the receiver. 14 Source Transport Process Source Transport Process Destination Transport Process Destination Transport Process TCP Segment ACK © 2011 Pearson Education, Inc. Publishing as Prentice Hall

15.  Each TCP segment sent by a side must have a sequence number. ◦ Simplest: 1,2,3,4,5,6,7 ◦ To detect lost or out-of-sequence messages ◦ TCP uses a more complex approach 15 1 1 4 4 2 2 5 5 3? © 2011 Pearson Education, Inc. Publishing as Prentice Hall

16.  TCP header has a 32-bit sequence number field. 16 Source Port # (16)Destination Port # (16) Sequence Number (32 bits) Acknowledgement Number (32 bits) Hdr Len (4) Flags (6)Window Size (16) Options (if any)PAD Reserved (6) TCP Checksum (16)Urgent Pointer (16) Data Field © 2011 Pearson Education, Inc. Publishing as Prentice Hall

17.  Initial Sequence Number is randomly selected by the sender; say, 79.  Sent in the sequence number field of the first TCP segment. 17 79 TCP Data Field TCP Header Sequence Number Field with Initial Sequence Number (79) © 2011 Pearson Education, Inc. Publishing as Prentice Hall

18.  Data octets in data fields of all segments in a connection are viewed as a long string.  TCP Segment 179  TCP Segment 280 81 82  TCP Segment 383 84 18 3 Octets in Data Field 2 Octets in Data Field ISN © 2011 Pearson Education, Inc. Publishing as Prentice Hall

19.  Supervisory segments, which contain a header but no data, are treated as carrying a single octet of data.  TCP seg 1898 899  TCP seg 2900  TCP seg 3901 902 … 19 Supervisory Segment Carries Data © 2011 Pearson Education, Inc. Publishing as Prentice Hall

20.  Sequence number field gets the value of the first octet in the data field.  TCP 179  TCP 280 81 82  TCP 383 84 20 80 is SeqNum Field Value 83 is SeqNum Field Value 79 is SeqNum Field Value © 2011 Pearson Education, Inc. Publishing as Prentice Hall

21.  Acknowledgement must indicate which TCP segment is being acknowledged. 21 Source TCP Process Source TCP Process Destination TCP Process Destination TCP Process TCP Segment ACK © 2011 Pearson Education, Inc. Publishing as Prentice Hall

22.  TCP header contains a 32-bit Acknowledgement Number field to designate the TCP segment being acknowledged. 22 Source Port # (16)Destination Port # (16) Sequence Number (32 bits) Acknowledgement Number (32 bits) Hdr Len (4) Flags (6)Window Size (16) Options (if any)PAD Reserved (6) TCP Checksum (16)Urgent Pointer (16) Data Field © 2011 Pearson Education, Inc. Publishing as Prentice Hall

23.  Acknowledgement Number field contains the next byte expected—the last byte of the segment being acknowledged, plus one.  TCP 179  TCP 280 81 82  TCP 383 84 23 83 is AckNum Field Value 85 is AckNum Field Value 80 is AckNum Field Value © 2011 Pearson Education, Inc. Publishing as Prentice Hall

24.  Quiz: A TCP segment contains the following data octets: ◦ 567, 568, 569, 570, 571, 572, 573, 574  What will be in the sequence number field of the TCP segment delivering the data?  What will be in the acknowledgement number field of the TCP segment acknowledging the TCP segment that delivers these octets? 24 © 2011 Pearson Education, Inc. Publishing as Prentice Hall

25.  Flow Control ◦ One TCP process transmits too fast. ◦ Other TCP process is overwhelmed. ◦ Receiver must control transmission rate. ◦ This is flow control. 25 TCP Process Too Much Data Flow Control Message © 2011 Pearson Education, Inc. Publishing as Prentice Hall

26.  A TCP segment has a Window Size field. ◦ Used in acknowledgements 26 Source Port # (16)Destination Port # (16) Sequence Number (32 bits) Acknowledgement Number (32 bits) Hdr Len (4) Flags (6) Window Size (16) Options (if any)PAD Reserved (6) TCP Checksum (16)Urgent Pointer (16) Data Field © 2011 Pearson Education, Inc. Publishing as Prentice Hall

27.  A TCP segment has a Window Size field. ◦ Tell how many more octets the sender can send beyond the segment being acknowledged 27 TCP Process Data Acknowledgement with Window Size Field © 2011 Pearson Education, Inc. Publishing as Prentice Hall

28.  Example ◦ TCP segment contained octets 45–89 ◦ Acknowledgement number for TCP segment acknowledging the segment is 90 ◦ If Window Size field value is 50, then ◦ Sender may send through octet 140 ◦ Must then stop unless the window has been extended in another acknowledgement 28 © 2011 Pearson Education, Inc. Publishing as Prentice Hall

29.  Each Acknowledgement extends the window of octets that may be sent. ◦ Called a sliding window protocol 29 1–4445 – 7980 – 419420 – 630 400 May send through 480 1 – 4445 – 7980 – 419420 – 630 500 May send through 920 © 2011 Pearson Education, Inc. Publishing as Prentice Hall

30.  TCP Segments have maximum data field sizes. ◦ (Size limit details are discussed later.) ◦ What if an application layer message is too large? 30 TCP HeaderTCP Data Field Max Application Layer Message © 2011 Pearson Education, Inc. Publishing as Prentice Hall

31.  Application layer message must be fragmented. ◦ Broken into several pieces ◦ Delivered in separate TCP segments 31 TCP HeaderTCP Data Field Max App Frag 1App Frag 2App Frag 3 © 2011 Pearson Education, Inc. Publishing as Prentice Hall

32.  Note that, in TCP fragmentation, the TCP segment is not fragmented. ◦ The application layer message is fragmented. 32 TCP HeaderTCP Data Field Max App Frag 1App Frag 2App Frag 3 © 2011 Pearson Education, Inc. Publishing as Prentice Hall

33.  Transport layer process on the source host does the fragmentation. ◦ Application layer on the source host is not involved ◦ Transparent to the application layer 33 Application Transport Internet Application Message TCP Segment © 2011 Pearson Education, Inc. Publishing as Prentice Hall

34.  Transport layer process on the destination host does the reassembly. ◦ Application layer on the destination host is not involved; gets original application layer message 34 Application Transport Internet Application Message TCP Segment © 2011 Pearson Education, Inc. Publishing as Prentice Hall

35.  What is the maximum TCP data field size? ◦ Complex  Maximum Segment Size (MSS) ◦ Maximum size of a TCP segment’s data field ◦ NOT maximum size of the segment as its name would suggest!!! 35 © 2011 Pearson Education, Inc. Publishing as Prentice Hall

36.  MSS Default is 536 octets. ◦ Maximum IP packet size any network must support is 576 octets.  Larger IP packets MAY be fragmented ◦ IP and TCP headers are 20 octets each if there are no options. ◦ This gives the default MSS of 536. ◦ Smaller if there are options in the IP or TCP header. 36 © 2011 Pearson Education, Inc. Publishing as Prentice Hall

37.  MSS Default is 536 octets. ◦ Suppose the application layer process is 1,000 octets long. ◦ Two TCP segments will be needed to send the data. ◦ The first can send the first 536 octets. ◦ The second can carry the remaining 464 octets of the application layer message. 37 © 2011 Pearson Education, Inc. Publishing as Prentice Hall

38.  Each side may announce a larger MSS. ◦ An option usually used in the initial SYN message it sends to the other. ◦ If announces MSS of 2,048, this many octets of data may be sent in each TCP segment. ◦ 536 is only the default—the value to use if no other value is specified by the other side. 38 © 2011 Pearson Education, Inc. Publishing as Prentice Hall

39. MultiplexingDetails of TCP operation IP mask operations IP Version 6IP fragmentationDynamic routing protocolsAddress Resolution ProtocolIP Address ClassesMobile IP 39 © 2011 Pearson Education, Inc. Publishing as Prentice Hall

40.  Masks were introduced in Chapter 9.  IP addresses alone do not tell you the size of their network or subnet parts.  Network Mask ◦ Has 1s in the network part ◦ Has 0s in the remaining bits  Subnet Mask ◦ Has 1s in the network plus subnet parts ◦ Has 0s in the remaining bits 40 © 2011 Pearson Education, Inc. Publishing as Prentice Hall

41.  Based on Logical AND ◦ Both must be true for the result to be true  Example ◦ 1010101010Data ◦ 1111100000Mask ◦ 1010100000Result 41 © 2011 Pearson Education, Inc. Publishing as Prentice Hall

42.  Based on Logical AND ◦ If mask bit is 1, get back original data ◦ If mask bit is 0, bet back zero  Example ◦ 1010101010Data ◦ 1111100000Mask ◦ 1010100000Result 42 © 2011 Pearson Education, Inc. Publishing as Prentice Hall

43.  IP packet arrives at a router ◦ Router sees destination IP address ◦ 11111111 01000000 10101010 00000000  Compares to each router forwarding table row ◦ Address Part in First Entry ◦ 11111111 01000000 00000000 00000000 ◦ Mask in First Entry ◦ 11111111 11100000 00000000 00000000 43 © 2011 Pearson Education, Inc. Publishing as Prentice Hall

44.  Mask the IP destination Address ◦ 11111111 01000000 10101010 00000000 (IP address) ◦ 11111111 11100000 00000000 00000000 (mask) ◦ 11111111 01000000 00000000 00000000 (result)  Compare Result with First Entry Address part ◦ 11111111 01000000 00000000 00000000 (address part) ◦ 11111111 01000000 00000000 00000000 (result)  The Entry is a Match! 44 © 2011 Pearson Education, Inc. Publishing as Prentice Hall

45.  Recap ◦ Read destination IP address of incoming IP packet. ◦ For each entry in the router forwarding table  Read the mask (prefix).  Mask the incoming IP address.  Compare the result with the entry’s IP address part.  Do they match or not? 45 © 2011 Pearson Education, Inc. Publishing as Prentice Hall

46.  Simple for Computers ◦ Computers have circuitry AND two numbers. ◦ Computers have circuitry to COMPARE two numbers to see if they are equal or not. ◦ Very computer-friendly, so used on routers.  Difficult for people, unfortunately 46 © 2011 Pearson Education, Inc. Publishing as Prentice Hall

47. MultiplexingDetails of TCP operationIP mask operations IP Version 6 IP fragmentationDynamic routing protocolsAddress Resolution ProtocolIP Address ClassesMobile IP 47 © 2011 Pearson Education, Inc. Publishing as Prentice Hall

48.  The dominant version of the Internet Protocol is Version 4 (v4). ◦ Earlier versions were not implemented  The emerging version is Version 6 (v6). ◦ V5 was defined but not implemented ◦ Informally called IPng (Next Generation)  IPv6 is already defined. ◦ Continuing improvements in V4 may delay its adoption 48 © 2011 Pearson Education, Inc. Publishing as Prentice Hall

49.  IPv6 raises the size of the Internet address field from 32 bits to 128 bits. ◦ We are running out of IP V4 addresses. ◦ V6 will solve the problem. ◦ But current work-arounds are delaying the need for IPv6 addresses—mostly Network Address Translation. 49 © 2011 Pearson Education, Inc. Publishing as Prentice Hall

50.  Improved Security ◦ But, through IPsec, v4 is being upgraded in security as well  Improved Quality of Service (QoS) ◦ But, under IETF Differentiated Services (diffserv) initiative, IPv4 is being upgraded in this area as well 50 © 2011 Pearson Education, Inc. Publishing as Prentice Hall

51.  Extension Headers ◦ IPv4 headers are complex. ◦ IPv6 basic header is simple. ◦ IPv6 uses extension headers for options. 51 Basic Header Extension Header 1 Extension Header 2 © 2011 Pearson Education, Inc. Publishing as Prentice Hall

52.  Extension Headers ◦ Basic header has 8-bit Next Header field ◦ Identifies first extension header or says that payload follows 52 Basic Header Extension Header 1 Extension Header 2 NH © 2011 Pearson Education, Inc. Publishing as Prentice Hall

53.  Extension Headers ◦ Each extension header also has 8-bit Next Header field ◦ Identifies next extension header or says that payload follows 53 Basic Header Extension Header 1 Extension Header 2 NH © 2011 Pearson Education, Inc. Publishing as Prentice Hall

54.  Extension Headers ◦ Next header field is an elegant way to allow options ◦ Easy to add new extension headers for new needs 54 Basic Header Extension Header 1 Extension Header 2 NH © 2011 Pearson Education, Inc. Publishing as Prentice Hall

55. MultiplexingDetails of TCP operationIP mask operationsIP Version 6 IP fragmentation Dynamic routing protocolsAddress Resolution ProtocolIP Address ClassesMobile IP 55 © 2011 Pearson Education, Inc. Publishing as Prentice Hall

56.  Maximum Transmission Unit (MTU) ◦ Largest IP packet a network will accept ◦ Arriving IP packet may be larger 56 IP Packet MTU © 2011 Pearson Education, Inc. Publishing as Prentice Hall

57.  If IP packet is longer than the MTU, the router breaks packet into smaller packets. ◦ Called IP fragments ◦ Fragments are still IP packets ◦ Earlier in Mod A, fragmentation in TCP 57 IP Packet 2 2 1 1 IP Packets Fragmentation MTU 3 3 © 2011 Pearson Education, Inc. Publishing as Prentice Hall

58.  What is Fragmented? ◦ Only the original data field ◦ New headers are created 58 IP Packet 2 2 1 1 IP Packets Fragmentation MTU 3 3 © 2011 Pearson Education, Inc. Publishing as Prentice Hall

59.  What Does the Fragmentation? ◦ The router ◦ Not the subnet 59 IP Packet 2 2 1 1 IP Packets Fragmentation MTU 3 3 © 2011 Pearson Education, Inc. Publishing as Prentice Hall

60.  Original packet may be fragmented multiple times along its route. 60 Destination Host Internet Process Source Host Internet Process Fragmentation © 2011 Pearson Education, Inc. Publishing as Prentice Hall

61.  Internet layer process on destination host defragments, restoring the original packet.  IP defragmentation only occurs once. 61 Destination Host Internet Process Defragmentation Source Host Internet Process © 2011 Pearson Education, Inc. Publishing as Prentice Hall

62.  More Fragments field (1 bit) ◦ 1 if more fragments ◦ 0 if not ◦ Source host internet process sets to 0 ◦ If router fragments, sets More Fragments field in last fragment to 0 ◦ In all other fragments, sets to 1 62 0011 Original IP PacketFragments © 2011 Pearson Education, Inc. Publishing as Prentice Hall

63.  IP packet has a 16-bit Identification field. 63 Total Length in Bytes (16) Time to Live (8) Options (if any) Version (4) Hdr Len (4) TOS (8) Identification(16 bits) Flags (3)Fragment Offset (13) Source IP Address Destination IP Address Header Checksum (16)Protocol (8) PAD Data Field © 2011 Pearson Education, Inc. Publishing as Prentice Hall

64.  IP packet has a 16-bit Identification field. ◦ Source host internet process places a number in the Identification field. ◦ Different for each original (non-fragmented) IP packet. 64 Total Length in Bytes (16) Time to Live (8) Version (4) Hdr Len (4) TOS (8) Identification(16 bits) Flags (3)Fragment Offset (13) Header Checksum (16)Protocol (8) © 2011 Pearson Education, Inc. Publishing as Prentice Hall

65.  IP packet has a 16-bit Identification field. ◦ If router fragments a packet, it places the original Identification field value in the Identification field of each fragment. 65 47 Original IP PacketFragments © 2011 Pearson Education, Inc. Publishing as Prentice Hall

66.  Purpose ◦ Allows receiving host’s internet layer process to know what fragments belong to each original packet ◦ Works even if an IP packet is fragmented several times 66 47 Original IP PacketFragments © 2011 Pearson Education, Inc. Publishing as Prentice Hall

67.  Fragment offset field (13 bits) is used to reorder fragments with the same Identification field.  Contains the data field’s starting point (in octets) from the start of the data field in the original IP packet. 67 Total Length in Bytes (16) Version (4) Hdr Len (4) TOS (8) Identification (16 bits)Flags (3) Fragment Offset (13) © 2011 Pearson Education, Inc. Publishing as Prentice Hall

68.  Receiving host’s internet layer process assembles fragments in order of increasing fragment offset field value.  This works even if fragments arrive out of order!  It works even if fragmentation occurs multiple times. 68 0212730 Fragment Offset Field © 2011 Pearson Education, Inc. Publishing as Prentice Hall

69.  IP Fragmentation ◦ Data field of a large IP packet is fragmented. ◦ The fragments are sent into a series of smaller IP packets fitting a network’s MTU. ◦ Fragmentation is done by routers. ◦ Fragmentation may be done multiple times along the route. 69 © 2011 Pearson Education, Inc. Publishing as Prentice Hall

70.  IP Defragmentation ◦ Defragmentation (reassembly) is done once, by destination host’s internet layer process. 70 © 2011 Pearson Education, Inc. Publishing as Prentice Hall

71.  All IP packets resulting from the fragmentation of the same original IP packet have the same Identification field value.  Destination host internet process orders all IP packets from the same original on the basis of their Fragment Offset field values.  More Fragments field tells whether there are no more fragments coming. 71 © 2011 Pearson Education, Inc. Publishing as Prentice Hall

72. MultiplexingDetails of TCP operationIP mask operationsIP Version 6IP fragmentation Dynamic routing protocols Address Resolution ProtocolIP Address ClassesMobile IP 72 © 2011 Pearson Education, Inc. Publishing as Prentice Hall

73.  Why Dynamic Routing Protocols? ◦ Each router acts independently, based on information in its router forwarding table. ◦ Dynamic routing protocols allow routers to share information in their router forwarding tables. 73 Router Forwarding Table Data © 2011 Pearson Education, Inc. Publishing as Prentice Hall

74.  Routing Information Protocol (RIP) is the simplest dynamic routing protocol. ◦ Each router broadcasts its entire routing table frequently. ◦ Broadcasting makes RIP unsuitable for large networks. 74 Routing Table © 2011 Pearson Education, Inc. Publishing as Prentice Hall

75.  RIP is the simplest dynamic routing protocol. ◦ Broadcasts go to hosts as well as to routers. ◦ RIP interrupts hosts frequently, slowing them down; unsuitable for large networks. 75 Routing Table © 2011 Pearson Education, Inc. Publishing as Prentice Hall

76.  RIP is limited. ◦ RIP routing table has a field to indicate the number of router hops to a distant host. ◦ The RIP maximum is 15 hops. ◦ Farther networks are ignored. ◦ Unsuitable for very large networks. 76 Hop © 2011 Pearson Education, Inc. Publishing as Prentice Hall

77.  Is a Distance Vector Protocol ◦ “New York” starts, announces itself with a RIP broadcast. ◦ “Chicago” learns that New York is one hop away. ◦ Passes this on in its broadcasts. 77 New YorkChicagoDallas 1 hop NY is 1 © 2011 Pearson Education, Inc. Publishing as Prentice Hall

78.  Learning Routing Information ◦ “Dallas” receives broadcast from Chicago. ◦ Already knows “Chicago” is one hop from Dallas. ◦ So New York must be two hops from Dallas. ◦ Places this information in its routing table. 78 New YorkChicagoDallas 1 hop NY is 1 NY is 2 © 2011 Pearson Education, Inc. Publishing as Prentice Hall

79.  Slow Convergence ◦ Convergence is getting correct routing tables after a failure in a router or link. ◦ RIP converges very slowly. ◦ May take minutes. ◦ During that time, many packets may be lost. 79 © 2011 Pearson Education, Inc. Publishing as Prentice Hall

80.  Encapsulation ◦ Carried in data field of UDP datagram  Port number is 520 ◦ UDP is unreliable, so RIP messages do not always get through. ◦ A single lost RIP message usually does little or no harm. 80 UDP Header UDP Data Field RIP Message © 2011 Pearson Education, Inc. Publishing as Prentice Hall

81.  Link State Protocol ◦ Link is a connection between two routers. ◦ OSPF routing table stores more information about each link than just its hop count: cost, reliability, and so on. ◦ Allows OSPF routers to optimize routing based on these variables. 81 Link © 2011 Pearson Education, Inc. Publishing as Prentice Hall

82.  Network is Divided into Areas. ◦ Each area has a designated router 82 Area Designated Router © 2011 Pearson Education, Inc. Publishing as Prentice Hall

83.  When a router senses a link state change ◦ Sends this information to the designated router 83 Area Designated Router Notice of Link State Change © 2011 Pearson Education, Inc. Publishing as Prentice Hall

84.  Designed router notifies all routers ◦ Within its area 84 Area Designated Router Notice of Link State Change © 2011 Pearson Education, Inc. Publishing as Prentice Hall

85.  Efficient ◦ Only routers are informed (not hosts). ◦ Usually only updates are transmitted, not whole tables. 85 Area Designated Router Notice of Link State Change © 2011 Pearson Education, Inc. Publishing as Prentice Hall

86.  Fast Convergence ◦ When a failure occurs, a router transmits the notice to the designated router. ◦ Designated router send the information back out to other routers immediately. 86 © 2011 Pearson Education, Inc. Publishing as Prentice Hall

87.  Encapsulation ◦ Carried in data field of IP packet  Protocol value is 89 ◦ IP is unreliable, so OSPF messages do not always get through. ◦ A single lost OSPF message usually does little or no harm. 87 IP Header IP Data Field OSPF Message © 2011 Pearson Education, Inc. Publishing as Prentice Hall

88.  Within a network you control, it is your choice. ◦ Your network is an autonomous system. ◦ Select RIP or OSPF based on your needs. ◦ Interior routing protocol. 88 © 2011 Pearson Education, Inc. Publishing as Prentice Hall

89.  RIP is fine for small networks. ◦ Easy to implement ◦ 15 hops is not a problem ◦ Broadcasting, interrupting hosts are not too important 89 © 2011 Pearson Education, Inc. Publishing as Prentice Hall

90.  OSPF is scalable. ◦ Works with networks of any size ◦ Management complexities are worth the cost in large networks 90 © 2011 Pearson Education, Inc. Publishing as Prentice Hall

91.  To connect different autonomous systems ◦ Must standardize cross-system routing information exchanges ◦ BGP is most popular today ◦ Gateway is the old name for router ◦ Exterior routing protocol 91 Autonomous System Autonomous System BGP © 2011 Pearson Education, Inc. Publishing as Prentice Hall

92.  Distance vector approach ◦ Number of hops to a distant system is stored in the router forwarding table  Normally only sends updates 92 Autonomous System Autonomous System BGP © 2011 Pearson Education, Inc. Publishing as Prentice Hall

93.  Encapsulation ◦ BGP uses TCP for delivery ◦ Reliable ◦ TCP is only for one-to-one connections ◦ If a border router connects to multiple external routers, must establish a TCP and BGP connection to each 93 Autonomous System Autonomous System BGP © 2011 Pearson Education, Inc. Publishing as Prentice Hall

94. MultiplexingDetails of TCP operationIP mask operationsIP Version 6IP fragmentationDynamic routing protocols Address Resolution Protocol IP Address ClassesMobile IP 94 © 2011 Pearson Education, Inc. Publishing as Prentice Hall

95.  Each host and router on a subnet needs a data link layer address to specify its address on the subnet. ◦ This address appears in the data link layer frame sent on a subnet. ◦ For instance, 48-bit 802.3 MAC layer frame addresses for LANs. 95 Subnet DA DL Frame for Subnet © 2011 Pearson Education, Inc. Publishing as Prentice Hall

96.  Each host and router also needs an IP address at the internet layer to designate its position in the overall Internet. 96 Subnet 128.171.17.13 © 2011 Pearson Education, Inc. Publishing as Prentice Hall

97.  IP address ◦ To guide delivery to destination host across the Internet (across multiple networks)  Subnet Address ◦ To guide delivery between two hosts, two routers, and a host and router within a single LAN, Frame Relay network, and so on 97 © 2011 Pearson Education, Inc. Publishing as Prentice Hall

98.  In a company, each person has a company- wide ID number (like IP address).  In a company, each person also has a local office number in a building.  Paychecks are made out to ID numbers.  For delivery, also need to know office number. 98 © 2011 Pearson Education, Inc. Publishing as Prentice Hall

99.  Problem ◦ Router knows that destination host is on its subnet based on the IP address of an arriving packet. ◦ Does not know the destination host’s subnet address, so cannot deliver the packet across the subnet. 99 Subnet 128.171.17.13 Subnet Address? Destination Host © 2011 Pearson Education, Inc. Publishing as Prentice Hall

100.  Router creates an ARP Request message to be sent to all hosts on the subnet. ◦ Address resolution protocol message asks “Who has IP address 128.171.17.13?” ◦ Passes ARP request to data link layer process for delivery. 100 Subnet ARP Request © 2011 Pearson Education, Inc. Publishing as Prentice Hall

101.  Data link process of router broadcasts the ARP Request message to all hosts on the subnet. ◦ On a LAN, MAC address of 48 ones tells all stations to pay attention to the frame. 101 Subnet ARP Request © 2011 Pearson Education, Inc. Publishing as Prentice Hall

102.  Host with IP address 128.171.17.13 responds. ◦ Internet process creates an ARP Response message. ◦ Contains the destination host’s subnet address (48-bit MAC address on a LAN). 102 Subnet ARP Response © 2011 Pearson Education, Inc. Publishing as Prentice Hall

103.  Router delivers the IP packet to the destination host. ◦ Places the IP packet in the subnet frame ◦ Puts the destination host’s subnet address in the destination address field of the frame 103 Subnet Deliver IP Packet within a Subnet Frame © 2011 Pearson Education, Inc. Publishing as Prentice Hall

104.  ARP Requests and Responses are sent between the internet layer processes on the router and the destination host. 104 Internet Process Router Internet Process Destination Host ARP Request ARP Response © 2011 Pearson Education, Inc. Publishing as Prentice Hall

105.  However, the data link processes deliver these ARP packets. ◦ Router broadcasts the ARP Request. ◦ Destination host sends ARP Response to the subnet source address found in the broadcast frame. 105 Internet Process Router Internet Process Destination Host Broadcast ARP Request Direct ARP Response Data Link Process Data Link Process © 2011 Pearson Education, Inc. Publishing as Prentice Hall

106. MultiplexingDetails of TCP operationIP mask operationsIP Version 6IP fragmentationDynamic routing protocolsAddress Resolution Protocol IP Address Classes Mobile IP 106 © 2011 Pearson Education, Inc. Publishing as Prentice Hall

107.  How large is the network part in an IP address?  Today we use network masks to tell.  Originally, IP had address classes with fixed numbers of bits in the network part. ◦ Class A: 8 bits (24 bits in local part) ◦ Class B: 16 bits (16 bits in local part) ◦ Class C: 24 bits (8 bits in local part) 107 © 2011 Pearson Education, Inc. Publishing as Prentice Hall

108.  All Class A IP addresses begin with 0.  7 remaining bits in network part. ◦ Only 128 possible Class A networks.  24 bits in local part. ◦ Over 16 million hosts per Class A network!  All Class A network parts are assigned or reserved. 108 © 2011 Pearson Education, Inc. Publishing as Prentice Hall

109.  All Class B IP address begin with 10 (1st zero in 2nd position).  14 remaining bits in network part ◦ Over 16,000 possible Class B networks  16 bits in local part ◦ Over 65,000 possible hosts  A good trade-off between number of networks and hosts per network  Most have been assigned 109 © 2011 Pearson Education, Inc. Publishing as Prentice Hall

110.  All Class C IP address begin with 110 (1st zero in 3d position).  21 more bits in network part ◦ Over 2 million possible Class C networks!  8 bits in local part ◦ Only 256 possible hosts per Class C network!  Unpopular, because large firms must have several 110 © 2011 Pearson Education, Inc. Publishing as Prentice Hall

111.  All Class D IP address begin with 1110.  Used for multicasting, not defining networks. ◦ Sending message to group of hosts ◦ Not just to one (unicasting) ◦ Not ALL hosts (broadcasting) ◦ Say, to send a videoconference stream to a group of receivers 111 © 2011 Pearson Education, Inc. Publishing as Prentice Hall

112.  All hosts in a multicast group listen for this multicast address as well as for their specific own host IP address. 112 Packets to Multicast Address Not in Group Reject In Group Accept In Group Accept © 2011 Pearson Education, Inc. Publishing as Prentice Hall

113.  Traditionally, unicasting and broadcasting ◦ Unicasting: send to one host ◦ Broadcasting: send to ALL hosts  Multicasting ◦ Send to SOME hosts ◦ 500 stations viewing a video course ◦ 50 computers getting software upgrades ◦ Standards exist and are improving ◦ Not widely used yet 113 © 2011 Pearson Education, Inc. Publishing as Prentice Hall

114.  Do not need to send an IP packet to each host ◦ Single packets go out ◦ Only multiplied when necessary 114 Single Packet Multiple Packets © 2011 Pearson Education, Inc. Publishing as Prentice Hall

115. MultiplexingDetails of TCP operationIP mask operationsIP Version 6IP fragmentationDynamic routing protocolsAddress Resolution ProtocolIP Address Classes Mobile IP 115 © 2011 Pearson Education, Inc. Publishing as Prentice Hall

116.  IP addresses are associated with fixed physical locations.  Mobile IP is needed for notebooks, other portable equipment.  Computer still gets a permanent IP address.  When travels, also gets a temporary IP address at its location.  This is linked dynamically to its permanent IP address. 116 © 2011 Pearson Education, Inc. Publishing as Prentice Hall

117. 117 All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, without the prior written permission of the publisher. Printed in the United States of America. Copyright © 2011 Pearson Education, Inc. Publishing as Prentice Hall