Chapter 6 Network Communications and Protocolssjkuyath/ETEE3281/ch06.pdf•65,534 hosts per network address –Class C: first octet between 192-223 •254 hosts per network address

Chapter 6

Network Communications and Protocols

Guide to Networking Essentials, Fifth Edition 2

Objectives

• Explain the function of protocols in a

network

• Describe common protocol suites


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


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


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


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


Protocols in a Layered Architecture


Protocols in a Layered Architecture


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


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


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


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


Transmission Control Protocol/Internet Protocol (TCP/IP)


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


IP, ICMP, and ARP in Action


IP, ICMP, and ARP in Action


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


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


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., 172.24.208.192

– Address has two parts: network and host ID

• E.g. 172.24.208.192 (172.24.0.0 and 208.192)

– 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


IP Addressing (continued)

• Classes

– Class A: first octet between 1-126

• 16,777,214 hosts per network address

– Class B: first octet between 128-191

• 65,534 hosts per network address

– Class C: first octet between 192-223

• 254 hosts per network address

– Class D: first octet between 224-239

• Reserved for multicasting

– Class E: first octet between 240-255

• Reserved for experimental use


IP Addressing (continued)

• 127.0.0.0 network is called the loopback address

– localhost always corresponds to address 127.0.0.1

• IETF reserved addresses for private networks

– Class A addresses beginning with 10

– Class B addresses from 172.16 to 172.31

– Class C addresses from 192.168.0 to 192.168.255

– 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)


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

– 192.203.187.0/26

– Subnetting divides network address in two or more

subnetwork addresses (with fewer host IDs for each)


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


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: 255.0.0.0

• Class B: 255.255.0.0

• Class C: 255.255.255.0


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


Converting Decimal to Binary

• 125 is converted to binary as follows:

– 125 divided by 2 equals 62, remainder 1








Converting Binary to Decimal

• To convert 11010011 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

5. 11010011, therefore, converts to:


High-Order Bit Patterns


Low-Order Bit Patterns


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 2n, 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 (2n-2)






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


Network Address Translation (NAT)


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 (169.254.x.x)


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


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


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


NetBIOS and NetBEUI


IPX/SPX


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


Implementing and Removing Protocols


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

Documents

Chapter 6 Network Communications and Protocolssjkuyath/ETEE3281/ch06.pdf•65,534 hosts per network address –Class C: first octet between 192-223 •254 hosts per network address