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Guide to TCP/IP, Third Edition

Guide to TCP/IP, Third Edition. Chapter 3: Data Link and Network Layer TCP/IP Protocols. Objectives. Understand the role that data link protocols, such as SLIP and PPP, play for TCP/IP Distinguish among various Ethernet and token ring frame types

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Guide to TCP/IP, Third Edition

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  1. Guide to TCP/IP, Third Edition Chapter 3: Data Link and Network Layer TCP/IP Protocols

  2. Objectives • Understand the role that data link protocols, such as SLIP and PPP, play for TCP/IP • Distinguish among various Ethernet and token ring frame types • Understand how hardware addresses work in a TCP/IP environment, and the services that ARP and RARP provide for such networks Guide to TCP/IP, Third Edtion

  3. Objectives (continued) • Appreciate the overwhelming importance of the Internet Protocol (IP), and how IP packets behave on TCP/IP networks • Understand the lifetime of an IP datagram, and the process of fragmentation and reassembly • Appreciate service delivery options • Understand IP header fields and functions Guide to TCP/IP, Third Edtion

  4. Data Link Protocols • Key jobs of Data Link layer • Media Access Control (MAC) • Logical Link Control (LLC) • Point-to-point data transfer • Shipping data from one MAC layer address to another Guide to TCP/IP, Third Edtion

  5. Data Link Protocols (continued) • WAN encapsulation of frames at Data Link layer involves one or more of the following services • Addressing • Bit-level integrity check • Delimitation • Protocol identification (PID) Guide to TCP/IP, Third Edtion

  6. Serial Line Internet Protocol (SLIP) • Original point-to-point protocol • Sometimes used to • Manage communications or networking equipment through a dial-up serial port connection • Simple packet-framing protocol described in RFC 1055 • Uses a special END character (0xC0) • Placed at the beginning and end of each IP datagram to delimit, or separate, each payload Guide to TCP/IP, Third Edtion

  7. Point-to-Point Protocol • Provides • Frame delimitation • Protocol identification and bit-level integrity check services • RFC 1661 includes • Encapsulation methods • A special Link Control Protocol (LCP) • A collection of negotiation protocols Guide to TCP/IP, Third Edtion

  8. Point-to-Point Protocol (continued) • Fields in the PPP header and trailer include • Flag • Protocol identifier • Frame Check Sequence (FCS) • Supports a default MTU of 1,500 bytes • Which makes it ideal for interconnecting Ethernet-based networks (or peers) Guide to TCP/IP, Third Edtion

  9. Special Handling for PPP Links • For switched technologies • Bidirectional connections must be negotiated between peers that wish to exchange data • X.25: RFC 1356. X.25 • Standard set of protocols defined in the 1970s by the International Telecommunications Union (ITU) • Frame relay: RFC 2427 • Assumes that digital-quality transmission lines are available for creating WAN links Guide to TCP/IP, Third Edtion

  10. Special Handling for PPP Links (continued) • ATM: RFCs 1577 and 1626 • High-speed, long-haul, broadband, cell-switched networking technology • Offers astonishing and ever-increasing bandwidth • PPPoE: RFC 2516 • Protocol used by Internet service providers to authenticate and manage broadband subscribers Guide to TCP/IP, Third Edtion

  11. Frame Types • At Data Link layer • Protocol data units are called frames • Frame • Represents same data that appears in digital form at the Network layer in an IP datagram Guide to TCP/IP, Third Edtion

  12. Ethernet Frame Types • Ethernet II frame type • De facto standardframe type used for IP datagram transmissions over Ethernet networks • Has protocol identification field • Ethernet frame types that TCP/IP can use • Ethernet II • Ethernet 802.2 Logical Link Control • Ethernet 802.2 Sub-Network Access Protocol (SNAP) Guide to TCP/IP, Third Edtion

  13. Ethernet II Frame Structure • Ethernet II frame type fields and structure • Preamble • Destination Address Field • Source Address Field • Type Field • Data Field • Frame Check Sequence Field Guide to TCP/IP, Third Edtion

  14. Ethernet II Frame Structure (continued) Guide to TCP/IP, Third Edtion

  15. Ethernet II Frame Structure (continued) Guide to TCP/IP, Third Edtion

  16. Ethernet 802.2 LLC Frame Structure • Unique fields • Preamble • Start Frame Delimiter Field: • Length Field • Destination Service Access Point (DSAP) Field: • Source Service Access Point (SSAP) Field: • Control Field • Destination Address • Source Address • Data • Frame Check Sequence Guide to TCP/IP, Third Edtion

  17. Ethernet 802.2 LLC Frame Structure (continued) Guide to TCP/IP, Third Edtion

  18. Ethernet 802.2 LLC Frame Structure (continued) Guide to TCP/IP, Third Edtion

  19. Ethernet SNAP Frame Structure • Fields • Organization Code Field • Ether Type Field • Preamble • Start Frame Delimiter • Destination Address • Source Address • Length • Destination Service Access Point • Source Service Access Point Guide to TCP/IP, Third Edtion

  20. Ethernet SNAP Frame Structure (continued) Guide to TCP/IP, Third Edtion

  21. Token Ring Frame Types • IEEE 802.5standard • Defines token ring networking • Token ring networks • Rely on a physical star design, although they use a logical ring transmission path • On a token ringnetwork • Each token ring workstation acts as a repeater • Variations of token ring frames • Token Ring 802.2 LLC frames • Token Ring SNAP frames Guide to TCP/IP, Third Edtion

  22. Token Ring Frame Types (continued) Guide to TCP/IP, Third Edtion

  23. Hardware Addresses in the IP Environment • IP addresses • Identify individual IP hosts on a TCP/IP internetwork • TCP/IP networking uses ARP to • Determine the hardware address of the local target for the packet • ARP cache • Table of hardware addresses learned through the ARP process Guide to TCP/IP, Third Edtion

  24. Hardware Addresses in the IP Environment (continued) Guide to TCP/IP, Third Edtion

  25. Hardware Addresses in the IP Environment (continued) Guide to TCP/IP, Third Edtion

  26. Hardware Addresses in the IP Environment (continued) Guide to TCP/IP, Third Edtion

  27. ARP Packet Fields and Functions • Basic ARP packets • Broadcast ARP request packet • Directed, or unicast, ARP reply packet • Most confusing part of ARP • Interpretation of the sender and target address information Guide to TCP/IP, Third Edtion

  28. ARP Packet Fields and Functions (continued) Guide to TCP/IP, Third Edtion

  29. ARP Packet Fields and Functions (continued) Guide to TCP/IP, Third Edtion

  30. ARP Cache • ARP information • Kept in an ARP cache in memory on most operating systems • Windows-based systems • Command arp -a is used to view the table contents • Have utility to view IP and hardware addresses Guide to TCP/IP, Third Edtion

  31. ARP Cache (continued) Guide to TCP/IP, Third Edtion

  32. Proxy ARP • Method that allows IP host to use a simplified subnetting design • Enables a router to “ARP” in response to an IP host’s ARP broadcasts • Most network configurations • May never need to use proxy ARP Guide to TCP/IP, Third Edtion

  33. Proxy ARP (continued) Guide to TCP/IP, Third Edtion

  34. Reverse ARP • Used to obtain an IP address for an associated data link address • Initially defined to • Enable diskless workstationsto find their own IP addresses upon booting or startup • BOOTP, and eventually DHCP, replaced RARP Guide to TCP/IP, Third Edtion

  35. About Internet Protocol • Network layer communications • End-to-end communications • Internet Protocol • Network layer protocol used in the TCP/IP suite • IP version 4 (IPv4) • Widely implemented • Internet Protocol version 6 (IPv6) • Most used in pilot or experimental implementations Guide to TCP/IP, Third Edtion

  36. Sending IP Datagrams • Requirements for building an IP datagram packet to transmit on the wire • IP addresses of the source and destination • Hardware address of the source and next-hop router • IP host • Can use a manually entered destination IP address or the DNS to obtain a destination’s IP address Guide to TCP/IP, Third Edtion

  37. Route Resolution Process • Enables IP host to determine if desired destination is local or remote • Local or Remote Destination? • Upon determination of IP address • IP host compares network portion of destination address to its own local network address Guide to TCP/IP, Third Edtion

  38. Route Resolution Process (continued) Guide to TCP/IP, Third Edtion

  39. If Remote, Which Router? • Types of route table entries • Host route entry • Network route entry • Receiving gateway typically does one of the following • Forwards packet • Sends an ICMP reply • Sends an ICMP reply indicating that it is unclear where to send the packet Guide to TCP/IP, Third Edtion

  40. Lifetime of an IP Datagram • IP packets • Have a pre-defined lifetime indicated in each packet’s Time to Live (TTL) field • 64 • Recommended starting TTL value • 128 • Default TTL in Windows 2000, Windows 2003, and Windows XP Guide to TCP/IP, Third Edtion

  41. Lifetime of an IP Datagram (continued) Guide to TCP/IP, Third Edtion

  42. Fragmentation and Reassembly • IP fragmentation • Enables a larger packet to be automatically fragmented by a router • Once fragmented • No reassembly occurs until fragments arrive at destination • All fragments are given the same TTL value Guide to TCP/IP, Third Edtion

  43. Service Delivery Options • Precedence • Used by routers to determine what packet to send • Type of Service • Used to select routing path when multiple pathsexist • Routing protocols • OSPF and Border Gateway Protocol (BGP) Guide to TCP/IP, Third Edtion

  44. Differentiated Services and Explicit Congestion Notification • RFC 2474, RFC 2475, and RFC 3168 • Offer a new use of the TOS field bits • Suggest that TOS and Precedence field bytes be replaced by a Differentiated Services Code Point (DSCP) field • Diffserv • Uses DSCP value to enable routers to offer varying levels of service to traffic based on marker placed in the DSCP field Guide to TCP/IP, Third Edtion

  45. IP Header Fields And Functions • Version Field • First field in IP header • Header Length Field • Denotes the length of the IP header only • Type of Service Field • Has two components: precedence and Type of Service • Total Length Field • Defines length of the IP header and any valid data Guide to TCP/IP, Third Edtion

  46. IP Header Fields And Functions (continued) Guide to TCP/IP, Third Edtion

  47. IP Header Fields And Functions (continued) • Identification Field • Each packet is given a unique ID value when sent • Flags Field • Three bits long • Typically, fragmentation is allowed • Fragment Offset Field • Shows where to place packet’s data when fragments are reassembled Guide to TCP/IP, Third Edtion

  48. IP Header Fields And Functions (continued) • Time to Live (TTL) Field • Denotes the remaining lifetime of the packet • Protocol Field • Indicates what is coming up next • Header Checksum Field • Provides error detection on the contents of the IP header only • Source Address Field • The IP address of the IP host that sent the packet Guide to TCP/IP, Third Edtion

  49. IP Header Fields And Functions (continued) • Destination Address Field • Can include a unicast, multicast, or broadcast address • Final destination of the packet • Options Fields • Exist primarily to provide additional IP routing controls • Can be useful when testing or debugging code or specific connections Guide to TCP/IP, Third Edtion

  50. Summary • Data link protocols • Manage transfer of datagrams across the network • At Data Link layer • Protocols must deliver services, such as delimitation, bit-level integrity checks, addressing, and protocol identification • Ethernet II frames • Most common frame type on LANs Guide to TCP/IP, Third Edtion

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