Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice HallChapter Five 1 Business Data Communications Chapter Five Network, Transport, and Application Layer Services

Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall Chapter Five 2 Primary Learning Objectives Understand the function of the application, transport, and network layers Explain IP classes and address formats Convert binary to decimal and decimal to binary Define subnetting Describe subnet masking Understand IP addressing guidelines Define supernetting

Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall Chapter Five 3 Application, Transport, and Network Layers The application layer is the highest level layer in the TCP/IP model This layer performs the functions of the application, presentation, and session layers in the OSI model The transport and network layers are the mid- level layers in the TCP/IP model Each of these three layers has special functions and responsibilities

Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall Chapter Five 4 Application, Transport, and Network Layers

Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall Chapter Five 5 Network Layer Sits above the data link and below the transport layers At its core is IP – Internetworking Protocol: IP’s key function is the transmittal of data packets IP has four assistants: Address Resolution Protocol Reverse Address Resolution Protocol Internet Control Message Protocol Internet Group Message Protocol

Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall Chapter Five 6 Network Layer Structure

Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall Chapter Five 7 Network Layer Services Address Resolution Protocol - ARP: To enable communication in a TCP/IP network, two key pieces of information are required: a device’s logical IP address, and its physical MAC address If a sending device knows the MAC address of a receiving device but not that device’s IP address, the sender’s network layer services broadcasts an ARP request ARP may find the requested information in the sender’s own memory or the memory of another local host, or have a router send out a request to other networks

Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall Chapter Five 8 Address Resolution Protocol

Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall Chapter Five 9 Network Layer Services Reverse Address Resolution Protocol – RARP: The opposite of ARP Sender knows the MAC address, but not the IP address RRAP is used mostly when a host device first boots up, and by diskless devices Diskless devices: Know their MAC, but not their IP address Can improve security, as they have no storage Can help prevent virus spread Can be cost effective May not be popular with users

Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall Chapter Five 10 Network Layer Services Internet Control Message Protocol – ICMP: IP has no error reporting or error correction controls ICMP supports IP by providing error reporting and query management ICMP can report five error types: Destination unreachable Source quench Time exceeded Parameter error Redirection

Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall Chapter Five 11 Network Layer Services Over a TCP/IP network two types of communication can occur: Unicasting and Multicasting Internet Group Message Protocol – IGMP: Used primarily when multicasting is required: Multicasting occurs when a sender wants to send to multiple receivers A multicast address can be used only as a destination, not as a source Multicast routers maintain lists of multicast addresses for groups of hosts

Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall Chapter Five 12 Network Layer Services

Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall Chapter Five 13 Network Layer Services

Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall Chapter Five 14 Network Layer Services Internet Group Message Protocol – IGMP: Supports two message types: Reporting Query Reporting messages are sent from a host to a router Query messages are sent from a router to a host

Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall Chapter Five 15 Transport Layer Has two key protocols: TCP and UDP Transmission Control Protocol User Datagram Protocol TCP is connection oriented and is called a reliable data stream – more overhead than UDP, but offers guarantees Here, “reliable” refers to a sender and receiver’s agreeing to establish a communication UDP is connectionless and is a non-reliable delivery service – more efficient, but no guarantee of delivery Sender and receiver do not have to agree to establish a communication

Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall Chapter Five 16 Transmission Control Protocol

Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall Chapter Five 17 User Datagram Protocol

Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall Chapter Five 18 Application Layer Fulfills the function of the application, presentation, and session layers of the OSI model Provides user connectivity to the network Supports a variety of protocols, including: Telnet FTP SMTP SNMP HTTP For application layer services, a client and/or server process has a specific, logical meaning

Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall Chapter Five 19 Application Layer - FTP

Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall Chapter Five 20 Application Layer - SMTP

Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall Chapter Five 21 IP Address Classes Logical IP network layer addresses fall into a categorization called classes IP address classes are categorized from A to E D and E are reserved and not commercially available As these addresses are logical, they can be modified Addressing schemes have to be developed by network administrators for the entire enterprise TCP/IP logical addresses have both a binary and a decimal equivalent

Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall Chapter Five 22 IP Address Classes

Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall Chapter Five 23 IP Address Classes

Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall Chapter Five 24 IP Address Classes

Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall Chapter Five 25 IP Address Classes

Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall Chapter Five 26 Subnetting IP addresses are often subdivided, creating “subnets” Subnetting allows a business to take a single allocated network IP address and create, internally, multiple subnets from that address

Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall Chapter Five 27 Subnetting An enterprise will often need more than one logical network IP address.

Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall Chapter Five 28 Subnetting IP addressing also requires a subnet mask The purpose of the subnet mask is to filter out the network and host portions of an IP address Each class, A, B, and C, has a standard, default subnet mask

Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall Chapter Five 29 Subnet Masks Class Subnet Mask in Decimal Subnet Mask in Binary A B C

Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall Chapter Five 30 Subnet Masks The same subnet mask must be used throughout the entire enterprise If a business chooses to modify its allocated network IP address for subnetting, the standard subnet mask for that address must also be modified In subnetting, bits are borrowed from the host portion of an IP address, based on the number of network identifiers required

Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall Chapter Five 31 Subnetting and Subnet Masks The number of network identifiers possible from borrowing host bits is shown by formula Two to the power of the number of high order bits borrowed, then minus two, gives the number of new network identifiers available (2 2 – 2) = number of usable network addresses Two is subtracted because two network addresses, all zeros or all ones, are reserved for special use

Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall Chapter Five 32 Subnetting and Subnet Masks Assume you have one allocated network IP address Also assume you need five network identifiers: If two high-order bits were borrowed, the result would be: 2 2 – 2 = 2 additional network addresses available. Not enough bits were borrowed If three high-order bits were borrowed, the result would be: 2 3 – 2 = 6 additional network addresses available. Enough bits were borrowed

Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall Chapter Five 33 Subnetting and Subnet Masks Given a single Class B, IP address: The default subnet mask would be: We want five network IP addresses, not one We borrow three high-order bits from the host portion of the IP address It is critical to remember that high-order bits are borrowed, and they have corresponding decimal values

Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall Chapter Five 34 Subnetting and Subnet Masks

Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall Chapter Five 35 Subnetting and Subnet Masks With three high-order bits borrowed, the following bit patterns are possible: Original IP address: In the table, 000 and 111 are not allowed, leaving the values in between New Network Addresses Possible:

Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall Chapter Five 36 Subnetting and Subnet Masks An IP address is compared to the subnet mask in a process called ANDing ANDing performs a bit-by-bit comparison of a given IP address and the submit mask This bit-by-bit comparison reveals the true network and host values from a given IP address ANDing enables a sender to determine if a receiver is on the same or another logical network

Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall Chapter Five 37 IP Addressing Guidelines Choose an addressing scheme that accommodates future growth Verify that each host within a LAN has a unique address Ensure that each network within an enterprise has a unique address Do not assign restricted addresses Use ranges of host addresses to identify specific types of devices Keep documentation current, accurate, accessible

Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall Chapter Five 38 IP Addressing – Possible Guidelines

Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall Chapter Five 39 Supernetting Subnetting borrows bits from the host to create more networks Supernetting borrows bits from the network to create more hosts Supernetting might be an option for a business holding several Class C addresses Supernetting requires that the addresses being supernetted be contiguous Supernetting is a function of Classless Inter-Domain Routing, or CIDR

Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall Chapter Five 40 In Summary The application, transport, and network layers provide high- and middle-layer services Addressing is a critical component of an enterprise’s data communications structure Most organizations use subnetting Subnetting generally requires modification of standard subnet masking IP addressing schemes should be well thought out and documented