Chapter 12: Internetworking and the Internet Principles of Computer Networks and Communications M. Barry Dumas and Morris Schwartz

Chapter 12:Internetworking and the

Internet

Principles of Computer Principles of Computer Networks and CommunicationsNetworks and Communications

M. Barry Dumas and Morris SchwartzM. Barry Dumas and Morris Schwartz

Principles of Computer Networks and Communications

2Chapter 12

Objectives

Define and explain internetworks and intranets Describe the Internet’s topology and explain why its

structure might be described as pseudo-hierarchical Discuss the beginnings of the World Wide Web, its

evolution and its relation to the Internet Describe Internet networking with the client/server model Explain the composition of URLs and examine

addressing issues Discuss issues associated with IPv4 addressing and the

move from IPv4 to IPv6


3Chapter 12

Overview Internetwork: a group of autonomous networks

Company internets and intranets typically revolve around LANs When varying locations are involved,

use WANs

Hierarchies help organize provider access

The issue of names and addresses on the Internet is complex Classful vs. Classless addressing

The IPv4 system will soon be out of addresses A move to IPv6 system is necessary

When these networks use TCP/IP protocols, they’re called extranets


4Chapter 12

Overview

Company internet Company-owned network, typically revolves around the LAN Uses LAN protocols (e.g., ethernet, token-ring, etc.) Designed only to be reached by authorized employees

Company intranet Company-owned, in-house network Uses TCP/IP protocols Designed only to be reached by authorized employees

Company extranet Company-owned, special outsider access to in-house network Uses TCP/IP protocols Connects between the owner company and networks of

“participating organizations” (e.g., suppliers, outsourcers, etc.)


5Chapter 12

History of the Internet Revisited

Usually traced back to its precursor, the ARPANET project Main concern—interconnecting independent (mainframe)

computers Later concern—the development of a robust internetwork

That could keep military communications flowing That could deal with complicated communications with incompatible

networks

Can be linked to the Advanced Research Projects Agency (ARPA) The U.S. response to the 1957 USSR launch

of the Sputnik


6Chapter 12

Internet Topology and Access

Service providers Organizations whose nodes and links supply all of the interconnections

Order of main hierarchy International Internet service providers (IISPs) and

national service providers (NSPs) at the top Most NSPs are also IISPs

Regional service providers (RSPs) Local Internet service providers (ISPs) at the bottom

“The topology of the Internet . . . is a pseudo-hierarchical structure based on links among

different levels of service providers.”

Many providers connect directly to each other, whether at the same or different levels

Local providers offer dial-up access, bringing the telephone system into the picture


7Chapter 12


National service providers (NSPs) Form the Internet backbone that extends worldwide Are private companies that own and maintain

the backbone networks Basic global interconnections are provided by NSPs linked to

each other through network access points (NAPs) NAPs are complex switching stations NAPs are privately owned, usually by companies other than NSPs

Some NSPs bypass NAPs to link directly to each other using peering points in their switching offices

Peering points are like the POPs of telephone companies’ end offices


8Chapter 12


Regional service providers (RSPs) Through routers

Connect hierarchically to NSPs Connect directly to other RSPs

Local Internet service providers (ISPs) Can link to NSPs, RSPs, and ISPs

The higher up on the hierarchy, the faster the links and the greater their capacity

ISPs can support many connection types Dial-up, cable modem, DSL, ATM, frame relay, Ethernet Not all ISPs can support all types

Most individuals and businesses

use ISPs to connect


9Chapter 12

Basic Topology of the Internet

Fig. 12.1

NSPs are linked to each other by NAPs

Some RSPs connect directly to each other by routers

Some NSPs connect directly to each other by peering points


10Chapter 12

Internet2 and Abilene Internet2

Nonprofit development project Academic, industry, government partnership Led by more than 200 universities

Purpose—to create advanced technologies and applications that can be adopted by the Internet

Will eventually lead to the “Internet of the future” Formation and constituency are reminiscent

of predecessors

Abilene High-speed wide-bandwidth

optical backbone network Designed to support Internet2

Abilene participants:—Indiana University—Juniper Networks—Nortel Networks—Qwest Communications in partnership with Internet2


11Chapter 12

The World Wide Web aka “the Web”

An interface that allows us to access the Internet

Tim Berners-Lee in 1990 Wrote the first World Wide Web server: httpd Created “WorldWideWeb”

the first client a hypertext browser/editor

Web browser software Simplified the information-finding process on the Internet

providing easy-to-use Web interfaces Websites

Collections of files (pages) organized by links Via a structure called hypertext (that contains hyperlinks)

Hyperlinks are addresses that take us from page to page and site to site, and make traversing the Internet straightforward

Web interfaces:Microsoft Internet ExplorerNetscape NavigatorMozilla Firefox


12Chapter 12

The Client/Server Model Name refers to the association between network entities

Client software requests services Server software provides services

A software model, not a hardware model Because it is software based, the client/server model provides a

flexible and scalable architecture This explains its popularity

Different from master/slave relationship! Server software in server/client model

does not control the network Servers and clients operate independently

Servers and clients

only join for the request–response

relationship


13Chapter 12

The Client/Server Model Client/Server—how different types of software

running on network devices interact Examples

When you go to a website, your browser software (client) requests Web pages from the site’s Web server software (server)

You can download a file from an Internet server by using an FTP (file transfer protocol) client that requests the file from a server running FTP software (part of the TCP/IP protocol suite)

An application can be both a client and a server One time requesting services and

another time providing them This is common in peer-to-peer networks


14Chapter 12

The Challenge of Internetwork Addressing

Standardized protocols and procedures are key factors in Internet success To send a message, the system must

Resolve the location of the recipient machine Distinguish it from all the devices on the Internet

Computers on a shared medium LAN (not an internetwork) have unique flat physical addresses Makes recipients easy to identify, but Insufficient and impractical for internetworking!

Addresses do not contain any location information System would have to search every network in the internetwork

for the recipient machine


15Chapter 12

The Challenges of Internetwork Addressing

Hierarchical scheme Different levels identify

A particular network of the internetwork The physical machine address

Two architecture models Open systems interconnection (OSI) model

The medium access control (MAC) sublayer of the data link layer handles physical addresses

Network layer handles logical addresses

Transmission control protocol over Internet protocol (TCP/IP) model

Follows the same pattern as OSI, but with possibly different labels OSI data link layer is the TCP/IP data link or link layer OSI network layer is the TCP/IP network or Internet layer


16Chapter 12

Hierarchical Addresses

The postal system uses hierarchical addresses Zip codes, states, cities, streets, names, etc. Allows the post office to route mail in stages

Hierarchical network addresses similarly comprise groupings/segment Allow the system to route messages to general areas,

particular networks and subnetworks, and finally the destination machine

Addresses are constructed and routed in network layer (OSI) or internetwork layer (TCP/IP)

(Reviewing from Chapter 6)


17Chapter 12

Hierarchical Addresses Physical address is different from the network address

Physical address—refers to a particular device The physical address doesn’t change when the device is moved

Network address—refers only to the network in which the device resides

The network address changes when the device is moved!

Analogy An automobile VIN stays with the automobile (physical address)

if you move to a different state The license plate (network address) changes to be

state-specific


18Chapter 12

Addressing in the Internet

Replaced NCP (network control protocol) Major step towards today’s Internet Explains why the Internet uses TCP/IP model architecture

TCP/IP There is a single applications layer Communications functions are in the other layers

OSI Layers above transport focus on applications Layers below session deal with communications

“In 1983 ARPANET officially adopted TCP/IP as the standard communications protocol.”


19Chapter 12

Model Architectures

Fig. 12.2

Focused on applications

Focused on communications


20Chapter 12


Internet protocol (IP) address Used to identify a device for the Internet,

in the internet layer Different from a medium access control

(MAC) address IP address

Associated with a machine that may or may not be in a LAN A logical address at the internet layer May be changed without affecting the physical address

MAC address A physical address at the data link layer of a device on a LAN


21Chapter 12

Addressing in the Internet IP address

Can be Static

Assigned and fixed on the device by a network administrator Dynamic

Assigned to a device by a protocol process when the device links (logs on) to the Internet

Dynamic IP addresses are recycled—released when a device disconnects and available for assignment on another device

Is used by the Internet to route packets To reach a device, there must be a mapping of its IP

address to its physical address

In other words, the IP address must be associated with the device’s physical address


22Chapter 12


There are several protocols to do this mapping (i.e., IP address to physical address)

Address resolution protocol (ARP) Reverse address resolution protocol (RARP) Dynamic host configuration protocol (DHCP)

)More about these in Chapter 13…)


23Chapter 12

The Domain Name System Domain name

The alphabet version of an IP address on the Internet Domain name system (DNS)

Used by the internet to translate a domain name or e-mail address to an IP address

Every domain name and e-mail address Is globally unique Has a one-to-one relationship with a unique IP address

Resolving the domain name The process where DNS translates a typed domain name into

an IP address that the Internet uses to route the transmission

For example, www.icann.org resolves (translates)

into dotted quad notation as 192.0.34.65


24Chapter 12

The Domain Name System

E-mail addresses A computer program called a mail transfer agent sends e-mail

from one computer or mail server to another These agents use the DNS to find out where to deliver the email

Smooth operations in the DNS DNS is an interconnected hierarchical system of high-speed

servers running distributed domain name databases For translation, this system simply searches its databases, finds

the IP address for the name, and relays it back Centralized organization keeps the DNS up to date

Domain name registries are responsible for distributing domain names and IP addresses

while ensuring their uniqueness


25Chapter 12

The Parts of a URL

Uniform resource locator (URL) Is a symbolic meaning for specifying

a Web resource The Web server on which the resource resides The protocol that will be used to retrieve the resource

URL components are separated from each other by forward slashes, dots, and sometimes colons

Easiest to interpret from right to left The rightmost segment is called the top-level domain

(TLD)


26Chapter 12

Top-Level Domains (TLDs)

www.users.alvernia.edu

Five original TLDs .com for commercial enterprises .gov for government sites .net for organizations providing network services .mil for use by the military .org for nonprofit organizations and those that do not fit other designations

Because .com, .org, and .net characteristics have blurred over time, they are now referred to as generic TLDs (gTLDs)

TLD concept speeds up the searching process in the database because each partition is relatively small

TLD


27Chapter 12

Domain and Sub-domain Names

Domain namewww.users.alvernia.edu

Also called second-level domain To the left of the TLD, separated by a dot Specifies a particular network, an autonomous system (AS)

within the Internet

Sub-domain namewww.users.alvernia.edu

Narrows the location of the resource server


28Chapter 12

URL Server

Server (host) name www.users.alvernia.edu

Is located to the left of the sub-domain name Holds the requested resource

It is common practice to give the name www to the server

that hosts Web documents

However, it is not required!


29Chapter 12

Domain Name and URL Components

Fig 12.3

Combined domain name.cuny.edu specifies a particular

network within the Internet

www is a server at Baruch College

If you see a URL that ends after the TLD or after a subdirectory name, the extension/index.htm or /index.html is assumed


30Chapter 12

Specifying the File on the Server

Domain names Specify location of the server Do not explicitly specify the file (Web page) on the server

Beyond domain names We need the path to the file on the server

Path must include directories and the file name Path information is appended to the right of the TLD by a slash (/)

Examplewww.users.alvernia.edu/students/finalgrades/index.htm

/students is the directory where Web files for students are stored /finalgrades is the subdirectory where files specific to final grades

are stored /index.htm specifies one particular file


31Chapter 12

Specifying the File on the Server

.htm and .html Indicate that the file is written in hypertext

markup language (HTML) Are default file names that are automatically

searched for if no file name is given

Any URL with nothing after the TLD or a subdirectory name

assumes the extension /index.htm or /index.html


32Chapter 12

Specifying the File on the Server Specifying the protocol in the URL

Leftmost segment of the URL defines actions taken in response to particular requests

http:// is one of the most common Web protocols Stands for hypertext transfer protocol In a browser, sends a command to the site’s Web server to

download the page Part of the application layer of the TCP/IP suite A “stateless” protocol

Each command is performed independently Makes it difficult to create sites that interact with users


33Chapter 12

The Http Protocol and “Cookies”

Software like Java is used to overcome “stateless” protocol difficulties Used to write very small text files (cookies)

to the client’s hard drive Cookies contain “state” information Allow a server application to understand the http

requests that make up a continuous exchange


34Chapter 12

Other Identifiers https://

For sites that require secure transmissions, an s is added, indicating encryption

Unreachable without appropriate passwords ftp (file transfer protocol)

Commonly employed protocol Used for uploading and downloading files to and from ftp servers ftp is typically in the server name, but not required

Country identifier The country identification is part of the TLD, though separated from it

by a dot For example, BBC News has a United Kingdom identifiernews.bbc.co.uk When with the TLD, it is called a country code top-level domain (ccTLD)

There are more than 240 ccTLDs!


35Chapter 12

IPv4 IP addressing began with ARPANET 1981 IPv4 became the standard we use today

Hierarchical scheme Classes of addresses

Three logical arrangements/splits of the bits reserved for addresses For few organizations needing many host addresses

Few bits for network addresses, many for hosts For many companies with many hosts

Many bits for network addresses, but also many for hosts For the great many organizations with very few hosts

Many bits for network addresses, few for hosts


36Chapter 12

IPv4 Classful Addressing

“Classful”—most widely used type of IPv4 Consists of 32 bits arranged in the dotted quad format

Four 8-bit sections Makes up three unicast classes

Unicast—from one source to one destination Two-part addresses that split the 32-bits into network/host

Class A: 8 / 24 Class B: 16 / 16 Class C: 24 / 8

Class identifier bits (prefixes) are included in the network address part of the split

192 .0.34 .65


37Chapter 12

Classful Addressing Prefixes

Prefixes Identify class Are not part of the IP address

Class A is 0 Class B is 10 Class C is 110 D (not classful) is 1110 E (not classful) is 1111


38Chapter 12

IPv4 Classful Addressing

ClassPrefix

(1st 8-bit section)

Number of Networks

Number of Hosts

A 0 _ _ _ _ _ _ _ 27 – 2 = 126 224 – 2 = 16,777,214

B 10 _ _ _ _ _ _ 214 – 2 = 16,382 216 – 2 = 65,534

C 110 _ _ _ _ _ 221 – 2 = 2,097,150 28 – 2 = 254

These classes account for 87.5% of potentially available addresses

Table 12.1


39Chapter 12

IPv4 Non-Classful D and E Two other categories of bits reserved for

addresses D and E are not segmented into networks and hosts Both allow for 228 = 268,435,456 addresses

D Multicasting

From a source to multiple destinations

E Reserved for experimenting


40Chapter 12

Classful Addressing

An organization that applies for an IPv4 address Receives a network address with a block of

host addresses The size of this block is determined by class

If the organization can handle more addresses than it actually uses, the other addresses associated with the company’s block go unused

Significant limitation to classful addressing It wastes a lot of addresses

Soon they will run out of addresses!

To forestall this, classless addressing was implemented


41Chapter 12

Classful Addresses, Networks, Subnets, and Masks

Network ID A company receives a network ID when a classful

network address is assigned Network ID + host address all 0s = network address Used by outside routers to direct IP packets addressed

to the company Not assignable to any company host

No host ID can be all 0s

Logical IP networks A company subdivides the classful network address

to organize its own hosts


42Chapter 12

Subnets and Masks Subnets

Logical networks with their own subnet addresses Created by assigning hosts to groups with their own

subnet addresses Organized many ways—by building, floor, departmentMajor advantage:

Masks Bit patterns applied to entire addresses to isolate their

components Used to separate network, subnet, and host addresses Have the same number of bits (arranged in dotted quad

segments) as the IP address, but only use 1s and 0s

A single IP address can connect a whole subnet to the Internet


43Chapter 12

Bitwise Multiplication and Masks

Bitwise multiplication of the address by the mask Equivalent to applying the “and” operator Captures address parts where mask bits are 1

and ignores where they are 0 Internet routers easily identify the IP address class

by finding bit patterns this way

Class B mask


44Chapter 12


When the class is identified, a network default mask is applied

Three default masks Class A mask: 255.0.0.0 Class B mask: 255.255.0.0 Class C mask: 255.255.255.0


45Chapter 12


In operation After one of the three default masks is applied, the

network address is revealed

The network address is assigned to the edge router of the organization

When a packet reaches any router, the appropriate mask is applied If the network address it finds is not for that organization,

the packet is passed to the next hop router If the network and router addresses match, a subnet mask

is applied


46Chapter 12


Subnet address Comprises the network address + subnet mask bits

The remaining host address bits are all 0s The total number of bits in the combined network and

subnet addresses is indicated by a /n notation at the end of the address

16 bits 3 bits = 19 bits

130.57.110.9/19


47Chapter 12

Classless Addresses

A solution to the IP address shortage?

Classless addressing All of IPv4’s address space of 32 bits would be

available without restriction Twice as many addresses could be created

But addressing hierarchy and restrictions needed Otherwise, routers would be overwhelmed and

complicated


48Chapter 12

Classless Addresses

Classless inter-domain routing (CIDR) The compromise between classful and classless

Allows any number of leftmost bits to be assigned as a network address Addresses assigned based on the number of hosts a

network can support; no class designation CIDR is not limited to network addresses of 8,16,or 24 bits

CIDR is NOT perfect Still wastes addresses, just not as many as classful

addressing


49Chapter 12

CIDR, Subnetting, and Supernetting

Supernetting CIDR’s hierarchical scheme that parallels subnetting One key difference—it is applied to routing outside

of the organization (hence the name) Is a method of route aggression

A single high-level routing table entry represents many lower-level routes

Internet backbone routers need fewer entries More efficient, eases table size requirements


50Chapter 12

IPv6

Uses a 128-bit address sequence instead of 32

Provides IP header extensions

Adds quality of service (QoS) labeling to IP packets

Uses coloned octal, not dotted quad

Accommodates CIDR by adding a (an) /n to the end of the address


51Chapter 12

IPv6

Uses a 128-bit address sequence instead of 32 increases the number of available IP addresses allows for additional hierarchy levels that improve routing efficiency




Accommodates CIDR by adding a /n to the end of the address


52Chapter 12

IPv6


Provides IP header extensions Improve privacy, authentication, and integrity





53Chapter 12

IPv6



Adds quality of service (QoS) labeling to IP packets Specifies the level of service requests

Priority, real-time, normal handling




54Chapter 12

IPv6

Uses coloned octal, not dotted quad Eight segments separated by colons Two bytes per segment Typically written in hexadecimal notation

Still 32 characters, one hexadecimal digit = 2 bytes Leading 0s in each section are eliminated for simplification BUT, only one string of 0s can be removed in a given address


55Chapter 12

IPv6





Accommodates CIDR by adding a /n to the end of the address n is the number of bits in the CIDR prefix


56Chapter 12

IPv4 Packet Headers

Fig. 12.4IPv4


57Chapter 12

IPv6 Packet Headers

Fig. 12.4IPv6


58Chapter 12

Methods for Moving from IPv4 to IPv6

Dual stack What?

Stack—the IP protocols used by the network nodes (routers, hosts) Dual stack—nodes that contain the stacks for both IP versions

How? The sender queries the DNS for an address

If the address is IPv4, the packet is sent as IPv4 If the address is IPv6, the packet is sent as IPv6

Pro Network nodes accommodate both IPv4 and IPv6

Con Each of the dual stack nodes must have an IPv4 address

Address scarcity is not alleviated Processing through two stacks adds to switching time


59Chapter 12


Tunneling Why?

A packet from an IPv6 node or region of nodes (a cloud) may have to travel across an IPv4 cloud to reach another IPv6 node

How? An IPv4 tunnel is created for it to travel through

First it needs an IPv4 address from the IPv6 edge router at the IPv4/IPv6 border

The IPv6 router will encapsulate it into an IPv4 packet At the other border, the IPv4 edge router will then decapsulate this packet

Pro Avoids having to assign IPv4 addresses to IPv6-only nodes within a

capsule Con

Additional processing at the borders


60Chapter 12

Transitioning from IPv4 to IPv6

Fig. 12.5A

Both IPv4 and IPv6 addresses are maintained

The sender uses whatever packet format (i.e., IPv4 or IPv6)

is returned from the DNS server for the destination node


61Chapter 12

Transitioning from IPv4 to IPv6

Fig. 12.5BAn IPv4 header encapsulates IPv6 packets

while transiting through IPv4 regions


62Chapter 12


Translation Why?

An IPv4-only host cannot understand packets from a IPv6-only host Tunneling will not help resolve this problem

The packet is still IPv6 after the encapsulating header is removed How?

At the least, the edge router must translate the IPv6 header into an IPv4 header

Pro IPv4 hosts and IPv6 hosts can communicate

Con Translation can be complicated!

The end node processes can involve the IP protocols themselves

Documents

Chapter 12: Internetworking and the Internet Principles of Computer Networks and Communications M. Barry Dumas and Morris Schwartz