Chapter 6 Network Communications and Protocols

Guide to Networking Essentials, Fifth Edition2 Contents 1.Protocols 1.1. The Function of Protocols 1.2. Protocols in a Layered Architecture 2.Common Protocol Suites 2.1. Transmission Control Protocol/Internet Protocol (TCP/IP) 2.2. IP Addressing 2.3. Other Protocol Suites 2.4. Implementing and Removing Protocols

Guide to Networking Essentials, Fifth Edition3 1. Protocols Strictly speaking, protocols are the rules and procedures for communicating –For two computers to communicate, they must speak the same language and agree on the rules of communication

Guide to Networking Essentials, Fifth Edition The Function of Protocols As protocols serve their functions in the OSI model, they might work at one or many layers When a set of protocols works cooperatively, it’s called a protocol stack or protocol suite –The most common protocol stack is TCP/IP, the Internet protocol suite –IPX/SPX, used in older versions of Novell NetWare, is disappearing as companies upgrade to newer versions of NetWare –Levels of a protocol stack map to their functions in the OSI model

Guide to Networking Essentials, Fifth Edition Connectionless Versus Connection- Oriented Protocols Protocols that use connectionless delivery place data on the network and assume it will get through –Connectionless protocols aren’t entirely reliable –Are fast: little overhead, don’t waste time establishing/managing/tearing down connections Connection-oriented protocols are more reliable and, consequently, slower –Two computers establish a connection before data transfer begins In a connection, data is sent in an orderly fashion –Ensures that all data is received and is accurate, or that suitable error messages are generated

Guide to Networking Essentials, Fifth Edition Routable Versus Nonroutable Protocols The network layer (OSI) is responsible for moving data across multiple networks –Routers are responsible for routing process Protocol suites that function at Network layer are routable or routed protocols; otherwise, they are called nonroutable –TCP/IP and IPX/SPX are routable protocols –An older and nearly obsolete protocol, NetBEUI, is a nonroutable protocol that works well in small networks, but its performance drops considerably as a network grows

Guide to Networking Essentials, Fifth Edition Protocols in a Layered Architecture

Guide to Networking Essentials, Fifth Edition8

Network Protocols Some popular network protocols include: –Internet Protocol version 4 (IPv4 or simply IP) Provides addressing and routing information –Internetwork Packet Exchange (IPX) Novell’s protocol for packet routing and forwarding Belongs to the IPX/SPX protocol suite Serves many of the same functions as TCP/IP’s IP –Internet Protocol version 6 (IPv6) A new version of IP that’s being implemented on many current networking devices and operating systems –Addresses some weaknesses of IPv4

Guide to Networking Essentials, Fifth Edition Transport Protocols Transport protocols can be connection-oriented (reliable) or connectionless (best-effort) delivery –Transmission Control Protocol (TCP) Responsible for reliable data delivery in TCP/IP –Sequential Packet Exchange (SPX) Novell’s connection-oriented protocol used to guarantee data delivery –NetBIOS/NetBEUI NetBIOS establishes/manages communications between computers and provides naming services NetBEUI provides data transport services for these communications

Guide to Networking Essentials, Fifth Edition Application Protocols Application protocols provide services to client applications –Simple Mail Transport Protocol (SMTP) in TCP/IP –File Transfer Protocol (FTP) in TCP/IP –Simple Network Management Protocol (SNMP) Manages and monitors network devices (TCP/IP) –NetWare Core Protocol (NCP) Novell’s client shells and redirectors –AppleTalk File Protocol (AFP) Apple’s remote file-management protocol

Guide to Networking Essentials, Fifth Edition12 2. Common Protocol Suites Because most protocols contain a combination of components, these components are usually bundled as a protocol suite –TCP/IP Dominates the networking arena to the point of making most of the other suites nearly obsolete –IPX/SPX –NetBIOS/NetBEUI –AppleTalk

Guide to Networking Essentials, Fifth Edition Transmission Control Protocol/Internet Protocol (TCP/IP)

Guide to Networking Essentials, Fifth Edition TCP/IP Network Layer Protocols Internet Protocol version 4 (IPv4) is a Network layer protocol that provides source and destination addressing and routing for the TCP/IP suite –Connectionless protocol; fast but unreliable Internet Control Message Protocol (ICMP) is a Network layer protocol used to send error and control messages between systems or devices –The Ping utility uses ICMP to request a response from a remote host to verify availability Address Resolution Protocol (ARP) resolves logical (IP) addresses to physical (MAC) addresses

Guide to Networking Essentials, Fifth Edition15 IP, ICMP, and ARP in Action

Guide to Networking Essentials, Fifth Edition16

Guide to Networking Essentials, Fifth Edition TCP/IP Transport Layer Protocols Transmission Control Protocol (TCP) is the primary Internet transport protocol –Connection oriented using a three-way handshake –Message fragmentation and reassembly –Uses acknowledgements to ensure that all data was received and to provide flow control User Datagram Protocol (UDP) is connectionless –Generally faster, although less reliable, than TCP Doesn’t segment data or resequence packets Doesn’t use acknowledgements for reliability Used by NFS and DNS

Guide to Networking Essentials, Fifth Edition TCP/IP Application Layer Protocols Domain Name System (DNS) –Session layer name-to-address resolution protocol Hypertext Transport Protocol (HTTP) –To transfer Web pages from Web server to browser File Transfer Protocol (FTP) –For file transfer and directory and file manipulation Telnet –Remote terminal emulation; operates at layers 7-5 Simple Mail Transport Protocol (SMTP) –Operates at layers 7-5; provides messaging services

Guide to Networking Essentials, Fifth Edition IP Addressing Logical addresses are 32 bits (4 bytes) long –Each byte is represented as an octet (decimal number from 0 to 255) –Usually represented in dotted decimal notation E.g., –Address has two parts: network and host ID E.g ( and ) –Categorized into ranges referred to as classes Class system provides basis for determining which part of address is the network and which is the host ID The first octet of an address denotes its class

Guide to Networking Essentials, Fifth Edition20 Classes –Class A: first octet between ,777,214 hosts per network address –Class B: first octet between ,534 hosts per network address –Class C: first octet between hosts per network address –Class D: first octet between Reserved for multicasting –Class E: first octet between Reserved for experimental use

Guide to Networking Essentials, Fifth Edition network is called the loopback address –localhost always corresponds to address IETF reserved addresses for private networks –Class A addresses beginning with 10 –Class B addresses from to –Class C addresses from to –These addresses can’t be routed across the Internet –To access the Internet, NAT is needed –IPv6 eliminates need for private addressing; provides a 128-bit address (vs. IPv4’s 32 bits)

Guide to Networking Essentials, Fifth Edition Classless Interdomain Routing (CIDR) Addressing by class has been superseded by a more flexible addressing method –Classless Interdomain Routing (CIDR) –The network and host demarcation can be made with any number of bits from beginning of address –E.g., a Class C address’s network section is 24 bits Using CIDR, an address registry can assign an address with a network section of 26 bits – /26 –Subnetting divides network address in two or more subnetwork addresses (with fewer host IDs for each)

Guide to Networking Essentials, Fifth Edition Why Subnet? Subnetting –Makes more efficient use of available IP addresses –Enables dividing networks into logical groups –Can make network communication more efficient Broadcast frames are sent to all computers on the same IP network –Hubs and switches forward broadcast frames; routers do not –Broadcast domain: extent to which a broadcast frame is forwarded without going through a router –Subnetting reduces broadcast traffic

Guide to Networking Essentials, Fifth Edition Subnet Masks Subnet mask determines which part of address denotes network portion and which denotes host –32-bit number –A binary 1 signifies that the corresponding bit in the IP address belongs to the network portion; a 0 signifies that bit in address belongs to host portion –Default subnet mask uses a 255 in each octet in address that corresponds to the network portion Class A: Class B: Class C:

Guide to Networking Essentials, Fifth Edition Some Simple Binary Arithmetic Four kinds of binary calculations: –Converting between binary and decimal –Converting between decimal and binary –Understanding how setting high-order bits to the value of 1 in 8-bit binary numbers corresponds to specific decimal numbers –Recognizing the decimal values for numbers that correspond to low-order bits when set to 1

Guide to Networking Essentials, Fifth Edition26 Converting Decimal to Binary 125 is converted to binary as follows: –125 divided by 2 equals 62, remainder 1 –62 divided by 2 equals 31, remainder 0 –31 divided by 2 equals 15, remainder 1 –15 divided by 2 equals 7, remainder 1 –7 divided by 2 equals 3, remainder 1 –3 divided by 2 equals 1, remainder 1 –1 divided by 2 equals 0, remainder 1

Guide to Networking Essentials, Fifth Edition27 Converting Binary to Decimal To convert to decimal: 1.Count the total number of digits in the number (8) 2.Subtract one from the total (8 - 1 = 7) 3.That number (7) is the power of 2 to associate with the highest exponent for two in the number 4.Convert to exponential notation, using all the digits as multipliers , therefore, converts to:

Guide to Networking Essentials, Fifth Edition28 High-Order Bit Patterns

Guide to Networking Essentials, Fifth Edition29 Low-Order Bit Patterns

Guide to Networking Essentials, Fifth Edition30 Calculating a Subnet Mask To decide how to build a subnet mask: 1.Decide how many subnets you need 2.Decide how many bits you need to meet or exceed the number of required subnets Use the formula 2 n, with n representing the number of bits you must add to the starting subnet mask 3.Borrow bits from the top of the host portion of the address down 4.Ensure that you have enough host bits available to assign to computers on each subnet (2 n -2)

Guide to Networking Essentials, Fifth Edition31

Guide to Networking Essentials, Fifth Edition32

Guide to Networking Essentials, Fifth Edition33 Calculating Supernets Supernetting “borrows” bits from network portion of an IP address to “lend” those bits to host portion –Permits consecutive IP network addresses to be combined and viewed in a single logical network Combining two or more small networks into one larger network is only one reason to supernet –Supernetting can combine multiple routing table entries into a single entry, which can drastically decrease the table’s size on Internet routers –This reduction in routing table size increases the speed and efficiency of Internet routers

Guide to Networking Essentials, Fifth Edition Network Address Translation (NAT)

Guide to Networking Essentials, Fifth Edition Dynamic Host Configuration Protocol (DHCP) Detailed configuration of devices, keeping track of assigned addresses and to which machine they were assigned, etc., is difficult in large networks –DHCP was developed to make this process easier –DHCP server must be configured with a block of available IP addresses and their subnet masks –Clients must be configured to use DHCP Broadcast request message is sent on boot –Client leases the address the server assigns to it –If no answer is received, in an APIPA-enabled OS, the computer assigns itself an address ( x.x)

Guide to Networking Essentials, Fifth Edition Internet Protocol Version 6 (IPv6) IPv6 solves several IPv4 problems –Limiting 32-bit address space An IPv6 address is 128 bits long –Lack of built-in security IPSec provides authentication and encryption –A sometimes complicated setup IPv6 is autoconfiguring (stateless or stateful) –Lack of built-in QoS QoS headers in IPv6 packets can identify packets that require special or priority handling, making applications such as streaming audio and video much easier to implement

Guide to Networking Essentials, Fifth Edition37 IPv6 Addresses IPv6 addresses are specified in hexadecimal format in 16-bit sections separated by a colon –Longhand notation: 2001:260:0:0:0:2ed3:340:ab –Shorthand notation: 2001:260::2ed3:340:ab If one of the 16-bit numbers doesn’t require four hexadecimal digits, the leading 0s are omitted –Addresses have a three-part addressing hierarchy A public topology (first three 16-bit sections) A site topology (next 16 bits) An interface identifier (last 64 bits) –Derived from the MAC address on the host’s NIC

Guide to Networking Essentials, Fifth Edition Other Protocol Suites Other protocol suites are sometimes used on older networks, where the need to change to TCP/IP is not warranted, or in environments suited to the suite’s features –NetBIOS/NetBEUI Used primarily on older Windows networks –IPX/SPX Designed for use on NetWare networks –AppleTalk Used almost exclusively on Macintosh networks

Guide to Networking Essentials, Fifth Edition NetBIOS and NetBEUI

Guide to Networking Essentials, Fifth Edition IPX/SPX

Guide to Networking Essentials, Fifth Edition AppleTalk Although the AppleTalk standard defines physical transport in Apple Macintosh networks, it also establishes a suite of protocols those computers use to communicate Apple created AppleTalk Phase II to allow connectivity outside the Macintosh world AppleTalk divides computers into zones –Allow a network administrator to logically group computers and other resources that have frequent communication, in a manner similar to subnetting

Guide to Networking Essentials, Fifth Edition Implementing and Removing Protocols

Guide to Networking Essentials, Fifth Edition43 Summary Many protocols are available for network communications, each with its strengths/weaknesses The TCP/IP protocol suite dominates network communication in part due to its use on the Internet IP addressing involves several concepts, including address classes, subnetting, and supernetting IPv6 will eventually replace IPv4 because it offers several advantages: 128-bit address space, autoconfiguration, built-in security, and QoS