Unix Networking & Internetworking

History

Overview

DNS

Typical Communication Utilities

 Internet research started in the 1960’s

ARPA – Advanced Research Planning Agency

Began work on packet switching.

ARPANET – late 1970’s


Prototype Internet was developed.

Transmission Control Protocol/ Internet
Protocol

1 st used by academic institutions, research organizations, & the U.S. military.


1983 – Internet sites = 562

1986 – Internet sites = 2,308

Doubled every year for the next 10 years.

1996 – 9.5 million


Key to easy network utilization.

1 st browser – Mosaic – Developed by NCSA

National Center for Supercomputer
Applications.

Launched in 1991

Web browsing surpassed FTP

File Transfer Protocol


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.


Two or > hardware resources connected.

Can be computers, printers, plotters, scanners, etc.

A hardware resource is a host.


LAN – Local Area Network

MAN – Metropolitan Area Network

WAN – Wide Area Network

These distinctions are based on the maximum distance between hosts.


Local Area Network

Hosts are in a room, building, or close buildings

Distance from a few meters to about 1km


Metropolitan Area Networks

Hosts between a city or between small cities

Distance between hosts is about 1 to 20 km


Wide Area Network

Hosts distance range from tens of kilometers to a few thousand kilometers.


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 – Connect similar networks

Gateways – Connect dissimilar networts.
Convert messages to suitable form for each network.


Sharing resources – Printers, plotters, scanners, software, etc.

Communication between people

Costs savings

Reliability > 1 computer


Kernel handles the communications.

The communications hardware (NIC)

Network Interface Card

The Unix kernel handles the details.


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


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


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


Resolver functions like:
 gethostbyname

To invoke DNS service

Maps a host name to its IP address
 gethostbyaddr

Maps an IP address to its hostname

 ifconfig command

View the IP address & other info about your hosts interface to the network.

Usually in the /sbin directory

(Type /sbin/ifconfig)

 nslookup

Display the IP address of a host
 nslookup ibm.com

Returns the address.

Modern forms: host or dig


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)


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 .


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.


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 using hosts on a network.
 rwho – Remote who

Displays users using machines on your network.
 rwho –a Users currently idle

 ping – If host is alive it echoes a datagram.
 whereis – Finds the location
 finger – Display information about a user


Size of networks continues to grow.

Big problem – Too many servers.

Usually one server per application – 1 for data base, 1 for accounting, etc.


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.


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


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

Email Address

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.


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)

 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.


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 Command Example

The mail Command (Read Mail)


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

 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.


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

Figure 7-10
Local login

Figure 7-11
Remote Login

 rlogin host

 rlogin paris rlogin –l username host
 exit to leave
 telnet from UNIX

 telnet open host


 close quit
Shortcut: telnet host


SSH or Open SSH

Encrypted connections
 ssh –l loginID remote.machine.name

Corporate earnings are up 45% this quarter
1 ssh installed
Corporate earnings are up 45% this quarter
3 ssh installed
Client
Decrypt
Server
2
Encrypt fdh37djf246gs’b[da,\ssk

 ftp
 open host

Shortcut: ftp host
 login
 password
 ftp help: ?
 ftp command help: ? Command

? binary
 quit


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


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


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


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


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

 tar –x filename.tar destinationdirectory

Use ls to confirm that the extracted files are in the directory you specified.


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

 uncompress filename.z

Use ls to confirm that the uncompressed file is there (the .z file should be gone)