Lecture 9 Unix Networking (see chapter 7) Unix Networking & Internetworking History Overview DNS Typical Communication Utilities
Dec 28, 2015
Lecture 9 Unix Networking(see chapter 7)
Unix Networking & InternetworkingHistoryOverviewDNSTypical 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.
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
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 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
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.
E-Mail Programs
Some Programs available in Unix/Linux Mail – most basic, low level mail command ELM PINE (PINE Is Not Elm), more user friendly text mail Outlook, GUI driven Eudora Netscape Mailer
The mail command
You can use the mail command in several ways: 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.
Header Editing
While editing a message you may use… ~h -- lets you edit the header (to, subject,
cc, bcc) These may also work:
~s -- edit the subject. ~t -- edit the to list. ~c -- edit the cc (carbon copy) list. ~b -- edit the bcc (blind carbon copy) list.
Message Editing Commands
Use these while writing the actual message ~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 reading commands
These commands are used in mail at the & prompt 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
C - Compose to write a message I or L - View messages Q - Quit
Remote Login
rlogin host rlogin paris rlogin –l username host exit to leave
telnet from UNIX telnet open host close quit Shortcut: telnet host
Encryption
Client
Corporate earnings are Corporate earnings are up 45% this quarterup 45% this quarter
1
Decrypt
Server
2
Encrypt
fdh37djf246gs’b[da,\ssk
3
Corporate earnings are Corporate earnings are up 45% this quarterup 45% this quarter
ssh installed ssh
installed
File Transfer Protocol: ftp
ftp open host Shortcut: ftp host login password ftp help: ? ftp command help: ? Command
? 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 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 Use wildcards
File Archival
Creating an archive file with tar 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
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 compress filename compress archivename.tar Confirm that compressed file (.z) created with ls
filename.z archivename.tar.z