Transcript Lec9 Networking

Lecture 9 Unix Networking
(see chapter 7)
Unix Networking & Internetworking
History
Overview
DNS
Typical Communication Utilities
Network History
 Internet research started in the 1960’s
 ARPA – Advanced Research Planning Agency
 Began work on packet switching.
 ARPANET – late 1970’s
TCP/IP
 Prototype Internet was developed.
 Transmission Control Protocol/ Internet
Protocol
 1st used by academic institutions, research
organizations, & the U.S. military.
Internet Growth
 1983 – Internet sites = 562
 1986 – Internet sites = 2,308
 Doubled every year for the next 10 years.
 1996 – 9.5 million
Web Browser
 Key to easy network utilization.
 1st browser – Mosaic – Developed by NCSA
 National Center for Supercomputer
Applications.
 Launched in 1991
 Web browsing surpassed FTP
 File Transfer Protocol
Size Now
 Between 50 – 100 million computers
 1 million computer networks
 Unix has a special role in that most of the
network protocols were initially implemented
on Unix platforms.
 Most servers run on Unix based machines.
Networks & Internetworks
 Two or > hardware resources connected.
 Can be computers, printers, plotters,
scanners, etc.
 A hardware resource is a host.
A typical network configuration
Network Types
 LAN – Local Area Network
 MAN – Metropolitan Area Network
 WAN – Wide Area Network
 These distinctions are based on the maximum
distance between hosts.
LAN
 Local Area Network
 Hosts are in a room, building, or close
buildings
 Distance from a few meters to about 1km
MAN
 Metropolitan Area Networks
 Hosts between a city or between small cities
 Distance between hosts is about 1 to 20 km
WAN
 Wide Area Network
 Hosts distance range from tens of kilometers
to a few thousand kilometers.
Internetwork
 Internetwork is a network of networks.
 Can connect networks within a campus or
networks thousands of kilometers apart.
 Connected with routers or gateways.
 Internet is an internetwork of tens of
thousands of networks
Routers & Gateways
 Routers – Connect similar networks
 Gateways – Connect dissimilar networts.
Convert messages to suitable
form for each network.
Reasons for Networks
 Sharing resources – Printers, plotters,
scanners, software, etc.
 Communication between people
 Costs savings
 Reliability > 1 computer
TCP/IP
 Kernel handles the communications.
 The communications hardware (NIC)
 Network Interface Card
 The Unix kernel handles the details.
DNS Name Server
 Domain name service (DNS) is central to the
Internet
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When URLs are entered in a Web browser, a
DNS server converts the name to an IP address,
allowing the client to send a packet to the Web
server as requested
The information in DNS can be thought of as an
inverted hierarchical tree, where the top of the
tree is called root and is represented by a period
Users typically don’t refer to roots, but to the last
part of domain names called top-level domains
DNS Name Server
DNS Name Server
Setting Up a DNS Name Server
 Resolving a domain to an IP address using
DNS, also called querying the DNS server,
stores, or caches, the conversion information
resulting in speedier DNS queries
 Each domain has a master DNS server which
contains database files that provide IP
addresses to every host in that domain
 Each domain should have a slave DNS server
which acts as a backup to the master
Setting Up a Basic Name
Server
 The program that implements a DNS server is
called named, the name daemon, which is
controlled by a system script in /etc/rc.d/init.d
 named is found in the BIND package on most
Linux systems; selecting the Red Hat Linux name
server component provides bind-conf, bind-utils,
and caching-nameserver
 Caching name servers have no preconfigured
domain information, but simply query other DNS
servers and cache the results
Name Server
 Resolver functions like:
 gethostbyname
 To invoke DNS service
 Maps a host name to its IP address
 gethostbyaddr
 Maps an IP address to its hostname
View Information
 ifconfig command
 View the IP address & other info about your
hosts interface to the network.
 Usually in the /sbin directory
 (Type /sbin/ifconfig)
View Information
 nslookup
 Display the IP address of a host
 nslookup ibm.com
 Returns the address.
 Modern forms:
host or dig
Popular Internet Services
 Electronic Mail – SMTP (Simple Mail
Transfer Protocol)
 File Transfer – FTP (File Transfer Protocol)
 Remote Login – Telnet (and ssh)
 Time – Time
 Web Browsing – HTTP (Hyper Text Transfer
Protocol)
Client-Server Model
 Internet services are implemented by service
partitioned in two parts.
 Part on the computer (host) where the user is
logged onto is the client software.
 The part that starts running when a server
boots is the server software.
Client-Server
 The server runs forever –
 Waiting for a client request
 A request is handled & then waits for another
request.
 Client starts running when a user runs the
program for a service the client offers.
Web Site
 URL – Universal Resource Locator
 URL is given to the client process to view a
page.
 http://machine
 Displays the home page of machine
List of users
 List of users using hosts on a network.
 rwho – Remote who
 Displays users using machines on your
network.
 rwho –a Users currently idle
Testing a network Connection
 ping – If host is alive it echoes a datagram.
 whereis – Finds the location
 finger – Display information about a user
Problem Areas
 Size of networks continues to grow.
 Big problem – Too many servers.
 Usually one server per application – 1 for
data base, 1 for accounting, etc.
Virtualization
 Virtualize the many servers employed.
 One server with the capability of replacing
many specialized servers.
 Goldman Sachs (brokerage firm) – Had 250
network people & 30 million lines of
specialized code.
 Large number of servers, regional, intl., etc.
Virtualization
 The number of specialist can be greatly
reduced.
 The network complexity can also be reduced.
 The one major problem is having one
machine for critical functions.
Typical Communication Utilities in UNIX
The talk Command
A Complete talk Session
A Complete talk Session
A Complete talk Session
The write Command
E-Mail Programs
 Some Programs available in Unix/Linux
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Mail – most basic, low level mail command
ELM
PINE (PINE Is Not Elm), more user friendly text mail
Outlook, GUI driven
Eudora
Netscape Mailer
Email Address
The mail command
The mail command
 You can use the mail command in several ways:
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mail -- by itself, it opens your messages and lets you
read them
mail person@address -- lets you compose a message to
someone at a certain address.
mail -s (subject) person@address -- lets you send a
message to someone at an address, with a certain subject.
mail -s (subject) person@address < text_file -- lets you
send a message to someone with text_file as the body of
the email.
Using mail
 When you are writing the mail message
body, use ^D or <enter> . <enter> to end
editing and send the message.
 If cc: shows up, this is a list of other
addresses you can enter if you wish to send a
message to other people.
 ^C will kill a mail message you are typing.
The mail Command (Sending Mail)
Header Editing
 While editing a message you may use…
 ~h -- lets you edit the header (to, subject,
cc, bcc)
 These may also work:
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~s
~t
~c
~b
-- edit the subject.
-- edit the to list.
-- edit the cc (carbon copy) list.
-- edit the bcc (blind carbon copy) list.
Message Editing Commands
 Use these while writing the actual message
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~r <file> -- Add a file into the message.
~f <num> -- add another email into the message
(forwarding).
~w <file> -- write the message to a file.
~q -- quit without saving
~p -- print the contents of the message.
Mail Command Example
The mail Command (Read Mail)
Mail reading commands
 These commands are used in mail at the &
prompt
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q -- quit and save
x -- quit without making any changes.
R or r -- reply to a message (r = senders and
recipients, R = senders only.)
f <numbers> -- view the message headers.
p or t <numbers> -- show those messages
More mail commands
 d <numbers> -- delete messages.
 u <numbers> -- undelete messages.
 s <numbers> <file> -- append the messages
to <file> with headers.
 w <numbers> <file> -- append messages to
<file> -- message only.
PINE
 A menu-driven client
 Uses pico as an editor
 Allows MIME attachments
 Main Menu
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C - Compose to write a message
I or L - View messages
Q - Quit
Figure 7-10
Local login
Figure 7-11
Remote Login
Remote Login
 rlogin host
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rlogin paris
rlogin –l username host
exit to leave
 telnet from UNIX
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telnet
open host
close
quit
Shortcut: telnet host
Secure Shell
 SSH or Open SSH
 Encrypted connections
 ssh –l loginID remote.machine.name
Encryption
Corporate earnings are
up 45% this quarter
Corporate earnings are
up 45% this quarter
1
3
ssh installed
ssh installed
Decrypt
Client
Server
2
Encrypt
fdh37djf246gs’b[da,\ssk
File Transfer Protocol: ftp
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ftp
open host
Shortcut: ftp host
login
password
ftp help: ?
ftp command help: ? Command
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? binary
 quit
Getting a file with ftp
 Use binary or bin if needed to go to binary
mode (default is ASCII)
 Use cd to go to the remote directory with your file
 Use lcd to go a directory on your local machine
(where you want the file to go after you ftp)
 Use get filename to copy a file from the
remote directory to the local directory
Getting many files with ftp
 Use binary or bin if needed to go to binary
mode (default is ASCII)
 Use cd to go to the remote directory with your
file
 Use lcd to go a directory on your local machine
(where you want the file to go after you ftp)
 Use mget to copy multiple files at once from the
remote directory to the local directory
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mget filename1 filename2 filename3
mget with wildcard: mget *
Toggle the prompt: prompt
Sending a file with ftp
 Use binary or bin if needed to go to
binary mode (default is ASCII)
 Use cd to go to the remote directory (where
you want to put your file)
 Use lcd to go a directory on your local
machine (where the file is located)
 Send the file using put filename
Sending many files with ftp
 Use binary or bin if needed to go to binary
mode (default is ASCII)
 Use cd to go to the remote directory with your file
 Use lcd to go a directory on your local machine
(where you want the file to go after you ftp)
 Use mput to copy multiple files at once from the
local directory to the remote directory
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Use wildcards
File Archival
 Creating an archive file with tar
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To archive everything in a directory,
tar –cf archivename originaldirectory
Use ls to confirm that a .tar file was created.
 Verify contents by viewing the table of contents
for the .tar file:
tar –tf archivename.tar
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Restoring tar files
 tar –x filename.tar destinationdirectory
 Use ls to confirm that the extracted files are in
the directory you specified.
File Compression
 Common compression programs: compress,
uncompress, PKZIP, PKUNZIP, pack, unpack
 Using compress
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compress filename
compress archivename.tar
Confirm that compressed file (.z) created with ls
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filename.z
archivename.tar.z
Uncompress
 uncompress filename.z
 Use ls to confirm that the uncompressed file
is there (the .z file should be gone)