The Internet is over 1.99 billion pages as of March 3, 2014 (http://www.worldwidewebsize.com). Searching the web without a search engine might be a little annoying because you would look at each website. Imagine looking at 1.99 billion pages! It would take you forever. Google.com is one of the popular search engines today and I'm sure you would be curious how it works.
Monday, March 3, 2014
Saturday, March 1, 2014
Ping Pong
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Ping is a basic Internet program that allows a user to verify
that a particular IP address exists
and can accept requests.
Ping is used diagnostically to ensure
that a host computer the user is trying to reach
is actually operating. Ping works by sending an Internet Control Message
Protocol (ICMP) Echo Request to a specified interface on the network and
waiting for a reply. Ping can be used for troubleshooting to test connectivity
and determine response time.
As a verb, ping means "to get the
attention of" or "to check for the presence of" another party
online. The computer acronym (for Packet Internet or Inter-Network Groper) was
contrived to match the submariners' term for the sound of a returned sonar
pulse.
Internet Protocol Address
The IP is the method or protocol by
which data is
sent from one computer to another on the Internet. Each computer (known as a host) on the Internet has at least one IP address that uniquely identifies it from all
other computers on the Internet.
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When you send or receive data (for example, an
e-mail note or a Web page), the message gets divided into little chunks called
packets. Each of these packets contains both the sender's Internet address and
the receiver's address. Any packet is
sent first to a gateway computer that understands a small part
of the Internet. The gateway computer reads the destination address and
forwards the packet to an adjacent gateway that in turn reads the destination
address and so forth across the Internet until one gateway recognizes the
packet as belonging to a computer within its immediate neighborhood or domain.
That gateway then forwards the packet directly to the computer whose address is
specified.
Because a message is divided into a number of
packets, each packet can, if necessary, be sent by a different route across the
Internet. Packets can arrive in a different order than the order they were sent
in. The IP just delivers them. It's up to another protocol, the TCP
to put them back in the right order.
IP is a connectionless protocol, which means that
there is no continuing connection between the end points that are
communicating. Each packet that travels through the Internet is treated as an
independent unit of data without any relation to any other unit of data. (The
reason the packets do get put in the right order is because of TCP, the
connection-oriented protocol that keeps track of the packet sequence in a
message.) In the OSI
communication model, IP is in layer 3, the Networking Layer.
The most widely used version of IP today is
Internet Protocol Version 4 (IPv4). However, IP Version 6 (IPv6) is also beginning to be supported. IPv6
provides for much longer addresses and therefore for the possibility of many
more Internet users. IPv6 includes the capabilities of IPv4 and any server that
can support IPv6 packets can also support IPv4 packets.
Domain Name Systems
The domain name system
(DNS) is the way that Internet domain names are located and translated into Internet Protocol addresses. A domain name is a
meaningful and easy-to-remember "handle" for an Internet address.
Because maintaining a central list of domain
name/IP address correspondences would be impractical, the lists of domain names
and IP addresses are distributed throughout the Internet in a hierarchy of
authority. There is probably a DNS server within close geographic proximity to
your access provider that maps the domain names in your
Internet requests or forwards them to other servers in the Internet.
Examples are:
.com, .edu, .gov, .org, .net, and many more.
Other Types of Protocols
Hypertext Transfer Protocol
The Hypertext Transfer Protocol
(HTTP) is the set of rules for transferring files (text, graphic
images, sound, video, and other multimedia files) on the World Wide Web.
As soon as a user opens their web browser, the user is indirectly making
use of HTTP. HTTP is an application protocol that runs on top of the TCP/IP suite
of protocols (the foundation protocols for the Internet).
HTTP concepts include (as the Hypertext
part of the name implies) the idea that files can contain references to other
files whose selection will elicit additional transfer requests. Any Web
server machine contains, in addition to the Web page files it can serve,
an HTTP daemon, a program that is designed to wait for HTTP requests and
handle them when they arrive. Your Web browser is an HTTP client,
sending requests to server machines. When the browser user enters file requests
by either "opening" a Web file (typing in a Uniform Resource Locator
or URL) or clicking on a hypertext link, the browser builds an
HTTP request and sends it to the IP address indicated by the URL. The
HTTP daemon in the destination server machine receives the request and sends
back the requested file or files associated with the request.
Hypertext Transfer
Protocol Secure
HTTPS (HTTP over SSL or HTTP Secure) is the use of Secure Socket Layer
(SSL) or Transport Layer Security (TLS) as a sublayer under regular HTTP
application layering. HTTPS encrypts and decrypts user page requests as well as
the pages that are returned by the Web server. The use of HTTPS protects
against eavesdropping and man-in-the-middle attacks. HTTPS was developed by Netscape.
HTTPS and SSL support the use of X.509 digital
certificates from the server so that, if necessary, a user can authenticate the
sender. Unless a different port is specified, HTTPS uses port 443
instead of HTTP port 80 in its interactions with the lower layer, TCP/IP.
Suppose you visit a Web site to view
their online catalog. When you're ready to order, you will be given a Web page
order form with a Uniform Resource Locator (URL) that starts with https://.
When you click "Send," to send the page back to the catalog retailer,
your browser's HTTPS layer will encrypt it. The acknowledgement you receive
from the server will also travel in encrypted form, arrive with an https:// URL,
and be decrypted for you by your browser's HTTPS sublayer.
The effectiveness of HTTPS can be
limited by poor implementation of browser or server software or a lack of
support for some algorithms. Furthermore, although HTTPS secures data as it
travels between the server and the client, once the data is decrypted at its
destination, it is only as secure as the host computer. That level of security
is analogous to "using an armored truck to transport money between two
persons.”
Simple
Mail Transfer Protocol
Simple Mail Transfer
Protocol (SMTP) is a TCP/IP protocol used
in sending and receiving e-mail. However, since it is limited in its ability to queue messages
at the receiving end, it is usually used with one of two other protocols, POP3 or IMAP,
that let the user save messages in a server mailbox and download them
periodically from the server. In other words, users typically use a program
that uses SMTP for sending e-mail and either POP3 or IMAP for receiving e-mail.
On Unix-based systems, sendmail is the most widely-used SMTP
server for e-mail. A commercial package, Sendmail, includes a POP3 server.
Microsoft Exchange includes an SMTP server and can also be set up to
include POP3 support.
SMTP usually is implemented to operate
over Internet port 25. An alternative to SMTP that is widely used in
Europe is X.400. Many mail servers now support Extended Simple Mail
Transfer Protocol (ESMTP), which allows multimedia files to be delivered as
e-mail.
File
Transfer Protocol
File Transfer Protocol (FTP) is a standard Internet protocol for
transmitting files between computers on the Internet. Like the Hypertext
Transfer Protocol (HTTP), which transfers displayable Web pages and related
files, and the Simple Mail Transfer Protocol (SMTP), which transfers e-mail,
FTP is an application protocol that uses the Internet's TCP/IP protocols.
FTP is commonly used to transfer Web page files from their creator to the
computer that acts as their server for everyone on the Internet. It's
also commonly used to download programs and other files to your computer from
other servers.
As a user, you can use FTP with a
simple command line interface (for example, from the Windows MS-DOS Prompt
window) or with a commercial program that offers a graphical user interface.
Your Web browser can also make FTP requests to download programs you select
from a Web page. Using FTP, you can also update (delete, rename, move, and
copy) files at a server. You need to logon to an FTP server. However,
publicly available files are easily accessed using anonymous FTP.
Basic FTP support is usually provided
as part of a suite of programs that come with TCP/IP. However, any FTP client
program with a graphical user interface usually must be downloaded from the
company that makes it.
Types of Protocols
Each
network protocol has its own contribution to the Internet. Let’s see how data travels in the Internet:
Internet Protocol
The Internet Protocol (IP) is the principal communications protocol in the Internet protocol suite for relaying datagrams across network boundaries. Its routing function enables internetworking,
and essentially establishes the Internet.
IP, as the primary
protocol in the Internet
layer of the Internet
protocol suite, has the task of delivering packets from
the source host to the destination host solely based
on the IP addresses in the packet headers. For this purpose, IP defines
packet structures that encapsulates the data to be delivered. It also
defines addressing methods that are used to label the datagram with source and
destination information.
Transmission Control Protocol
The Transmission Control Protocol (TCP) is a set of rules used along
with the IP to send data in the form of message units between computers over
the Internet. While IP takes care of handling the actual delivery of the data,
TCP takes care of keeping track of the individual units of data called packets that a message is divided into for
efficient routing through the Internet.
For example, when an HTML file is sent to you from a Web server,
the TCP program layer in that server
divides the file into one or more packets, numbers the packets, and then
forwards them individually to the IP program layer. Although each packet has
the same destination IP address, it may get routed differently through the
network. At the other end (the client program
in your computer), TCP reassembles the individual packets and waits until they
have arrived to forward them to you as a single file.
TCP is known as a connection-oriented protocol,
which means that a connection is established and maintained until such time as
the message or messages to be exchanged by the application programs at each end
have been exchanged. TCP is responsible for ensuring that a message is divided
into the packets that IP manages and for reassembling the packets back into the
complete message at the other end. In the Open Systems Interconnection (OSI)
communication model, TCP is in layer 4, the Transport Layer.
User Datagram Protocol
The User Datagram Protocol (UDP) is a communications protocol that
offers a limited amount of service when messages are exchanged between
computers in a network that uses the Internet Protocol (IP). UDP is an
alternative to the TCP
and, together with IP, is sometimes referred to as UDP/IP. Like the TCP, UDP
uses the IP to actually get a data unit (called a datagram) from one computer to another. Unlike
TCP, however, UDP does not provide the service of dividing a message into
packets and reassembling it at the other end. Specifically, UDP doesn't provide
sequencing of the packets that the data arrives in. This means that the
application program that uses UDP must be able to make sure that the entire
message has arrived and is in the right order. Network applications that want
to save processing time because they have very small data units to exchange
(and therefore very little message reassembling to do) may prefer UDP to TCP.
The Trivial File Transfer Protocol (TFTP) uses UDP instead of TCP.
UDP provides two services not provided by the IP
layer. It provides port numbers to help distinguish different user
requests and, optionally, a checksum capability
to verify that the data arrived intact.
In the OSI
communication model, UDP, like TCP, is in layer 4, the Transport Layer.
These
are just some of the many protocols. Some will be explained in the next post…
Protocols and DNS
A network protocol is a set of rules that
governs the communications between computers on a network. These rules include
Internet Protocol (IP), Transmission Control Protocol (TCP), User Datagram
Protocol (UDP), File Transfer Protocol (FTP), Simple Mail Transfer Protocol
(SMTP), Hypertext Transfer Protocol (HTTP), and so many more..jpg)
The Domain Name System (DNS) is a hierarchical distributed naming
system for computers, services, or any resource connected to the Internet or a
private network. The Domain Name System distributes the responsibility
of assigning domain names and mapping those names to IP addresses by
designating authoritative name servers for each domain. Authoritative name
servers are assigned to be responsible for their supported domains, and may
delegate authority over subdomains to other name servers. This mechanism
provides distributed and fault tolerant service and was designed to avoid the
need for a single central database.
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