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.

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 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 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: 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:

~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 Command Example

The mail Command (Read Mail)

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

Figure 7-10

Local login

Figure 7-11

Remote Login

Remote Login

rlogin host rlogin paris rlogin –l username host exit to leave

telnet from UNIX telnet open host close quit Shortcut: telnet host

Secure Shell

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

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

Uncompress

uncompress filename.z Use ls to confirm that the uncompressed file

is there (the .z file should be gone)