The Anarchist Cookbook (36 page)

Users must consult local documentation for specifics at their sites.

Names and Addresses In A Network

In DOD Protocol Suite, each network is given a unique identifying number. This number is

assigned by a central authority, namely the Network Information Center run by SRI,

abbreviated as SRI-NIC, in order to prevent more than one network from having the same

network number. For example, the ARPAnet has network number 10 while MIDnet has a

longer number, namely 128.242. Each host in a network has a unique identification so other

hosts can specify them unambiguously. Host numbers are usually assigned by the

organization that manages the network, rather than one central authority. Host numbers

do not need to be unique throughout the whole Internet but two hosts on the same

network need to have unique host numbers.

The combination of the network number and the host number is called the IP address of

the host and is specified as a 32-bit binary number. All IP addresses in the Internet are

expressible as 32-bit numbers, although they are often written in dotted decimal notation.

Dotted decimal notation breaks the 32-bit number into four eight-bit parts or octets and

each octet is specified as a decimal number. For example, 00000001 is the binary octet

that specifies the decimal number 1, while 11000000 specifies 192. Dotted decimal

notation makes IP addresses much easier to read and remember.

Computers in the Internet are also identified by hostnames, which are strings of

characters, such as "phrackvax." However, IP packets must specify the 32-bit IP address

instead of the hostname so some way to translating hostnames to IP addresses must

exist.

One way is to have a table of hostnames and their corresponding IP addresses, called a

hosttable. Nearly every TCP/IP implementation has such a hosttable, although the

weaknesses of this method are forcing a shift to a new scheme called the domain name

system. In UNIX systems, the hosttable is often called "/etc/hosts." You can usually

read this file and find out what the IP addresses of various hosts are. Other systems may

call this file by a different name and make it unavailable for public viewing.

Users of computers are generally given accounts to which all charges for computer use are

billed. Even if computer time is free at an installation, accounts are used to distinguish

between the users and enforce file protections. The generic term "username" will be used

in this file to refer to the name by which the computer account is accessed.

In the early days of the ARPAnet which was the first network to use the TCP/IP

protocols, computer users were identified by their username, followed by a commercial

"at" sign (@), followed by the hostname on which the account existed. Networks were not

given names, per se, although the IP address specified a network number.

For example, "knight@phrackvax" referred to user "knight" on host "phrackvax." This did

not specify which network "phrackvax" was on, although that information could be

obtained by examining the hosttable and the IP address for "phrackvax." (However,

"phrackvax" is a fictitious hostname used for this presentation.)

As time went on, every computer on the network had to have an entry in its hosttable for

every other computer on the network. When several networks linked together to form the

Internet, the problem of maintaining this central hosttable got out of hand. Therefore,

the domain name scheme was introduced to split up the hosttable and make it smaller and

easier to maintain.

In the new domain name scheme, users are still identified by their usernames, but hosts

are now identified by their hostname and any and all domains of which they are a part. For

example, the address "[email protected]" specifies username

"KNIGHT" on host "UMCVMB". However, host "UMCVMB" is a part of the domain

"MISSOURI" " which is in turn part of the domain "EDU". There are other domains in

"EDU", although only one is named "MISSOURI". In the domain "MISSOURI", there is

only one host named "UMCVMB".

However, other domains in "EDU" could theoretically have hosts named "UMCVMB"

(although I would say that this is rather unlikely in this example). Thus the combination of

hostname and all its domains makes it unique. The method of translating such names into

IP addresses is no longer as straightforward as looking up the hostname in a table.

Several protocols and specialized network software called nameservers and resolvers

implement the domain name scheme.

Not all TCP/IP implementations support domain names because it is rather new. In those

cases, the local hosttable provides the only way to translate hostnames to IP addresses.

The system manager of that computer will have to put an entry into the hosttable for

every host that users may want to connect to. In some cases, users may consult the

nameserver themselves to find out the IP address for a given hostname and then use that

IP address directly instead of a hostname.

I have selected a few network hosts to demonstrate how a host system can be specified

by both the hostname and host numerical address. Some of the nodes I have selected are

also nodes on BITnet, perhaps even some of the others that I do not make a note of due a

lack of omniscient awareness about each and every single host system in the world :-)

Numerical BITnetHostnameLocation
18.72.0.39ATHENA.MIT.EDUMass. Institute of

Technology MIT26.0.0.73SRI-NIC.ARPADDN Network Information Center

-36.21.0.13MACBETH.STANFORD.EDUStanford

University

?

36.21.0.60PORTIA.STANFORD.EDUStanford

University

?

128.2.11.131ANDREW.CMU.EDUCarnegie

Mellon

Univ.

ANDREW128.3.254.13LBL.GOVLawrence

Berkeley

Labrotories

LBL128.6.4.7RUTGERS.RUTGERS.EDURutgers

University

?

128«9.99.1CUCARD.MED.COLUMBIA.EDUColumbia

University

?

128.102.18.3AMES.ARC.NASA.GOVAmes

Research

Center

[NASA]

-128.103.1.1HARVARD.EDUHarvard University HARVARD128.111.24.40HUB.UCSB.EDUUniv.

Of Santa Barbara ?128.115.14.1LLL-WINKEN.LLNL.GOVLawrence Livermore Labratories

-128.143.2.7UVAARPA.VIRGINIA.EDUUniversity

of

Virginia

?

128.148.128.40BROWNVM.BROWN.EDUBrown

University

BROWN128.163.1«UKCC.UKY.EDUUniversity

of

Kentucky

UKCC128.183.10.4NSSDCA.GSFC.NASA.GOVGoddard Space Flight Center [NASA]-

128.186.4.18RAI.CC.FSU.EDUFlorida

State

University

FSU128.206.1.1UMCVMB.MISSOURI.EDUUniv.

of

MissouriColumbia

UMCVMB128.208.1.15MAX.ACS.WASHINGTON.EDUUniversity

of

Washington

MAX128.228.1.2CUNYVM.CUNY.EDUCity

University

of

New

York

CUNYVM129.10.1.6NUHUB.ACS.NORTHEASTERN.EDUNortheastern

University

NUHUB131.151.1.4UMRVMA.UMR.EDUUniversity

of

Missouri

Rolla

UMRVMA192.9.9.1SUN.COMSun Microsystems, Inc. -192.33.18.30VM1.NODAK.EDUNorth

Dakota State Univ. NDSUVM1192.33.18«0PLAINS.NODAK.EDUNorth Dakota State Univ.

NDSUVAX

Please Note: Not every system on BITnet has an IP address. Likewise, not every system

that has an IP address is on BITnet. Also, while some locations like Stanford University

may have nodes on BITnet and have hosts on the IP as well, this does not necessarily imply

that the systems on BITnet and on IP (the EDU domain in this case) are the same systems.

Attempts to gain unauthorized access to systems on the internet are not tolerated and is

legally a federal offense. At some hosts, they take this very seriously, especially the

government hosts such as NASA's Goddard Space Flight Center, where they do not mind

telling you so at the main prompt when you connect to their system.

However, some nodes are public access to an extent. The DDN Network Information

Center can be used by anyone. The server and database there have proven to be an

invaluable source of information when locating people, systems, and other information that

is related to the Internet.

Telnet

Remote login refers to logging in to a remote computer from a terminal connected to a

local computer. Telnet is the standard protocol in the DOD Protocol Suite for

accomplishing this. The "rlogin" program, provided with Berkeley UNIX systems and some

other systems, also enables remote login.

For purposes of discussion, the "local computer" is the computer to which your terminal is

directly connected while the "remote computer" is the computer on the network to which

you are communicating and to which your terminal is *NOT* directly connected.

Since some computers use a different method of attaching terminals to computers, a

better definition would be the following: The "local computer" is the computer that you

are currently using and the "remote computer" is the computer on the network with which

you are or will be communicating. Note that the terms "host" and "computer" are

synonymous in the following discussion.

To use Telnet, simply enter the command: TELNET

The prompt that Telnet gives is: Telnet>

(However, you can specify where you want to Telnet to immediately and bypass the

prompts and other delays by issuing the command: TELNET [location].)

There is help available by typing in ?. This prints a list of all the valid

subcommands that Telnet provides with a one-line explanation.

Telnet> ?

To connect to another computer, use the open subcommand to open a connection

to that computer. For example, to connect to the host "UMCVMB.MISSOURI.EDU",

do "open umcvmb.missouri.edu"

Telnet will resolve (i.e. Translate, the hostname "umcvmb.missouri.edu" into an

IP address and will send a packet to that host requesting login. If the remote

host decides to let you attempt a login, it prompts you for your username and password. If

the host does not respond, Telnet will "time out" (i.e. Wait for a reasonable amount of time

such as 20 seconds) and then terminate with a message such as "Host not responding."

If your computer does not have an entry for a remote host in its hosttable and it cannot

resolve the name, you can use the IP address explicitly in the telnet command. For

example,

TELNET 26.0.0.73 (Note: This is the IP address for the DDN Network Information

Center [SRI-NIC.ARPA])

If you are successful in logging in, your terminal is connected to the remote host. For all

intents and purposes, your terminal is directly hard-wired to that host and you should be

able to do anything on your remote terminal that you can do at any local terminal. There

are a few exceptions to this rule, however.

Telnet provides a network escape character, such as CONTROL-T. You can find out what

the escape character is by entering the "status" subcommand:

Telnet> status

You can change the escape character by entering the "escape" subcommand:

Telnet> escape

When you type in the escape character, the Telnet prompt returns to your screen and you

can enter subcommands. For example, to break the connection, which usually logs you off

the remote host, enter the subcommand "quit":

Telnet> quit

Your Telnet connection usually breaks when you log off the remote host, so the "quit"

subcommand is not usually used to log off.

When you are logged in to a remote computer via Telnet, remember that there is a time

delay between your local computer and the remote one. This often becomes apparent to

users when scrolling a long file across the terminal screen and they wish to cancel the

scrolling by typing CONTROL-C or something similar. After typing the special control

character, the scrolling continues. The special control character takes a certain amount of

time to reach the remote computer which is still scrolling information. Thus response from

the remote computer will not likely be as quick as response from a local computer. Once

you are remotely logged on, the computer you are logged on to effectively becomes your

"local computer," even though your original "local computer" still considers you logged on.

You can log on to a third computer which would then become your "local computer" and so

on. As you log out of each session, your previous session becomes active again.

File Transfer

FTP is the program that allows files to be sent from one computer to another.

"FTP" stands for "File Transfer Protocol".

When you start using FTP, a communications channel with another computer on the

network is opened. For example, to start using FTP and initiate a file transfer session with