Linux – Networking and the Internet
Intranet
- An inhouse Web site that serves the employees of the enterprise. Although
intranet pages may link to the Internet, an intranet is not a site accessed by
the general public.
Common Types of Network
Broadcast
– Such as Ethernet, any system attached to the network cable can send
messages at any time
Token
ring – such as FDDI (Fiber Distributed Data Interface),
only on e system can send a message at a time. A Token (Special Message) is
passed from one host to another around the ring.
Point to Point – Only two end points are involved.
LAN - (Local Area Network)
A communications network that serves users within a confined geographical
area. It is made up of servers, workstations, a network operating system and
a communications link.
Ethernet – The most widely used LAN access method
(Token Ring is the next most popular). Ethernet is normally a shared media
LAN. All stations on the segment share the total bandwidth, which is either 10
Mbps (Ethernet), 100 Mbps (Fast Ethernet) or 1000 Mbps (Gigabit Ethernet).
With switched Ethernet, each sender and receiver pair have the full bandwidth.
It uses:
· Thick coaxial cable
· Twisted Pair
· Fiber optics
WAN - (Wide Area Network) A
communications network that covers a wide geographic area, such as state or
country.
Computer communication
Packets – Message sent by the
computer that includes the address of the destination computer and the one
who sent it.
Router - A device that forwards
data packets from one local area network (LAN) or wide area network (WAN) to
another. Based on routing tables and routing protocols, routers read the
network address in each transmitted frame and make a decision on how to send
it based on the most expedient route (traffic load, line costs, speed, bad
lines, etc.).
Network Protocols
Protocol – common language used
by computers so that they can exchange information over networks. The protocol
determines the format of the message packet.
TCP/IP - (Transmission Control
Protocol/Internet Protocol) A communications protocol
developed under contract from the U.S. Department of Defense to internetwork
dissimilar systems. Invented by Vinton Cerf and Bob Kahn, this de facto UNIX
standard is the protocol of the Internet and has become the global standard
for communications.
UDP - (User Datagram
Protocol) A protocol within the TCP/IP protocol suite that is used in
place of TCP when a reliable delivery is not required. For example, UDP is
used for realtime audio and video traffic where lost packets are simply
ignored, because there is no time to retransmit. If UDP is used and a
reliable delivery is required, packet sequence checking and error
notification must be written into the applications
Other Protocols: SLIP (Serial
Line Internet Protocol), PPP ( Point to Point Protocol), and PLIP (Parallel
Line Internet Protocol)
Host Addresses
The physical address of a computer in a network. On the
Internet, a host address is the IP address of the machine. IE. 192.192.192.5 .
The address assignments are handled by a central authority an organization
named the Network Information Center (NIC)
Try visiting:
Find your own ip address http://www.ip-address.com/
Communication over the network and some utilities
$ finger - A UNIX command widely
used on the Internet to find out information about a particular user, such
as telephone number, whether currently logged on or the last time logged on.
The person being "fingered" must have placed his or her profile on
the system. Profiles can be very elaborate either as a method of social
introduction or to state particular job responsibilities. Fingering requires
entering the full user@domain address, if you have several machine on
your network. Otherwise you will have to type user@domain.something to
find information about a user located outside of your network.
[wmorales@rc33uxas01 wmorales]$ finger
Login Name Tty Idle Login Time Office Office Phone
jchen jchen pts/1 29 Nov 28 22:14 (pdx-dhcp-114.reflexnet.net)
wmorales Walter Morales pts/0 Nov 28 21:54
(c825382-a.bvrtn1.or.home.com)
$ hostname – Allows you to
identify the system that you are using
[wmorales@rc33uxas01 wmorales]$ hostname
rc33uxas01
[wmorales@rc33uxas01 wmorales]$
$ ruptime - Show the status of local
networked machines
$ rwho - The rwho command
produces output similar to who, but for all machines on your network
$ mail – Send an email message to
a user
$ talk – Allow to communicate
interactively with a remote user over the network
$ rlogin – (Remote LOGIN)
A UNIX command that allows users to remotely log onto a server in the
network as if they were at a terminal directly connected to that computer.
Rlogin is similar to the Telnet command, except that rlogin also passes
information to the server about the type of client machine, or terminal
$ telnet - A terminal emulation
protocol commonly used on the Internet and TCP/IP-based networks. It allows
a user at a terminal or computer to log onto a remote device and run a
program.
$ rsh - (Remote SHell)
A UNIX command that enables a user to remotely log into a server on the
network and pass commands to it. It is similar to the rlogin command, but
provides passing of command line arguments to the command interpreter on the
server at the same time
example% rsh lizard cat lizard.file >> example.file
appends the remote file lizard.file from the machine called
"lizard" to the file called example.file on the machine called
"example,"
while the command:
example% rsh lizard cat lizard.file ">>"
lizard.file2
appends the file lizard.file on the machine called
"lizard" to the file another.lizard.file which also resides on the
machine called "lizard."
$ rcp - Rcp copies files between
machines. Each file or directory argument is either a remote file name of
the form ``rname@rhost:path'', or a local file name (containing no `:'
characters, or a `/' before any `:'s).
$ rcp memo.921 bravo:memos/memo.921
The filename memo.921 is copied from the working
directory on the local system to the memos directory on bravo
$ ftp (File Transfer Protocol)
A protocol used to transfer files over a TCP/IP network (Internet, UNIX,
etc.). For example, after developing the HTML pages for a Web site on a
local machine, they are typically uploaded to the Web server using FTP.
$ ping (Packet INternet Groper)
An Internet utility used to determine whether a particular IP address is
online. It is used to test and debug a network by sending out a packet and
waiting for a response.
[wmorales@rc33uxas01 wmorales]$ ping psg.com
PING psg.com (147.28.0.62) from 198.106.33.1 : 56(84) bytes of
data.
64 bytes from psg.com (147.28.0.62): icmp_seq=0 ttl=245
time=45.600 msec
64 bytes from psg.com (147.28.0.62): icmp_seq=1 ttl=245
time=276.695 msec
64 bytes from psg.com (147.28.0.62): icmp_seq=2 ttl=245
time=26.915 msec
--- psg.com ping statistics ---
3 packets transmitted, 3 packets received, 0% packet loss
round-trip min/avg/max/mdev = 26.915/116.403/276.695/113.600
ms
[wmorales@rc33uxas01 wmorales]$
$ netstat - The netstat command symbolically displays
the contents of various
network-related data structures for active connections. The
Interval
parameter, specified in seconds, continuously displays
information
regarding packet traffic on the configured network interfaces.
$ traceroute - An Internet utility
that traces the route from the client machine to the remote host being
contacted. It reports the IP addresses of all the routers in between.
[wmorales@rc33uxas01 wmorales]$ /usr/sbin/traceroute psg.com
traceroute to psg.com (147.28.0.62), 30 hops max, 38 byte
packets
1 198.106.33.10 (198.106.33.10) 0.527 ms 0.468 ms 0.492 ms
2 192.220.63.153 (192.220.63.153) 0.957 ms 0.870 ms 0.852 ms
3 192.220.63.33 (192.220.63.33) 3.238 ms 3.083 ms 5.888 ms
4 192.220.63.14 (192.220.63.14) 3.761 ms 4.339 ms 4.197 ms
5 192.220.63.6 (192.220.63.6) 6.370 ms 7.631 ms 5.948 ms
6 d1-1-0-0-28.a02.ptldor01.us.ra.verio.net (199.238.102.114)
7.023 ms 6.922 ms 8.161 ms
7 ge-1-0-0.r01.ptldor01.us.bb.verio.net (129.250.30.145) 7.236
ms 9.388 ms 7.480 ms
8 p4-4-2.r02.sttlwa01.us.bb.verio.net (129.250.3.37) 11.371 ms
11.391 ms 11.213 ms
9 et-3-0.o00.sttlwa01.us.bb.verio.net (129.250.31.130) 12.465
ms 11.917 ms 12.157 ms
10 psg.o00.sttlwa01.us.bb.verio.net (129.250.16.238) 16.618 ms
16.908 ms 18.347 ms
11 psg.com (147.28.0.62) 20.513 ms 16.346 ms 17.101 ms
[wmorales@rc33uxas01 wmorales]$
Internet Services
USENET - (USEr NETwork) A public access
network on the Internet that provides user news and group e-mail. It is a
giant, dispersed bulletin board that is maintained by volunteers who provide
news and mail feeds to other nodes. All the news that travels over the
Internet is called "NetNews," and a running collection of messages
about a particular subject is called a "newsgroup." Usenet began
in 1979 as a bulletin board between two universities in North Carolina.
Today, there are more than 50,000 newsgroups. News can be read with a Web
browser or via newsreaders such as nn, rn, trn and tin
Examples of news groups:
soc.culture.brazil
comp.os.linux.help
pdx.forsale
$ rn or.forsale to read the newsgroup or.forsale
ARCHIE - (ARCHIvE) An Internet utility used
to search for file names. There are approximately 30 computer systems
throughout the Internet, called "Archie servers," that maintain
catalogs of files available for downloading from various FTP sites.
Periodically, Archie servers search FTP sites throughout the Internet and
record information about the files they find. If you do not have Archie,
some Internet hosts let you log on via Telnet as user "archie."
$ archie (if archie is on local
system)
$ telnet archie.uninett.no (to connect to an archie
server)
GOPHER - A program that searches
for file names and resources on the Internet and presents hierarchical menus
to the user. As users select options, they are moved to different Gopher
servers on the Internet. Where links have been established, Usenet news and
other information can be read directly from Gopher. There are more than
7,000 Gopher servers on the Internet
$ gopher (it works at cyberspace)
If you use a web browser type for instance gopher://gopher.voa.gov/
at the address location on the top of your browser.
LYNX - A text-based Web browser
created at the University of Kansas. Though largely supplanted by graphical
browsers such as Netscape Navigator and Internet Explorer, Lynx is still
popular among people with visual disabilities and those with very slow modem
connections.
Unix text based version of a web browser
$ lynx www.pcc.edu
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