Network Stacks & TCP/IP

Some _basic_ information on things related to the Internet and networks.
This article is basically a collection of useful information gathered from
varied
sources. This article is in no way what so ever meant to be any kind of
tutorial, it's only meant to show a few basic things that (IMOHO) everyone
should
know.

The OSI Reference model is a 7 layer stack representing the operation of a
network. It is the standard adopted by most everybody that networks. So, of
course M$ had to go and **** it up and make there own model for WinNT, and
once again be the [proprietary] bastards that they are. Anyway, when dealing
with network security knowing the basics of the OSI model can be quite
beneficial, and if you network heavily, it's a must. So here it is, the
basics
of the model:

The 7 layers are:

7 Application
6 Presentation
5 Session
4 Transport
3 Network (logical, eh?)
2 Data Link
1 [Physical]

Layer Seven: the Application Layer
I do believe that this layer is self-explanatory enough. This layer is made up
of the applications you use. i.e. X, Netscape, Quake III, FTP clients,
etc...

Layer Six: the Presentation Layer
Imagine you sitting in front of a person who speaks only a language that you do
not understand, and you must communicate with him. Or maybe you're on vacation
in another country and you're trying to get a chick's phone #. You need a
translator, right? That's what this layer does. It translates protocols and
such for the applications. Also handles encryption, network security, and
the character set information.

Layer Five: The Session Layer
A session is two computers connecting to each other and performing an act. Be
it a login or a file transfer or the like, once the session is over a new one begins.
Sending a file via FTP creates a session, the file is sent, and the session
is ended.

Layer Four: the Transport Layer
This layer makes sure the frames are error-free and troubleshoots problems with
transmission and reception. It can also combine several smaller frames into one, larger frame.

Layer Three: the Network Layer
This layer controls the traffic, like, determines optimal routing, logical to
physical addressing, and is the layer most associated with networking stuff
such a routers, bridges, switches, and the like.

Layer Two: the Data Link Layer
This layer packages data into frames to be sent, and unpacks the frames
that are received.

Layer One: the Physical Layer
The physical layer includes such things as cable, electrons, NICs(*), and
the such. The "physical" things.

What does all this mean? Well, first of all there is a LOT more to it, but I
do not wish to write a book on it. I strongly suggest TCP/IP for dummies,
seriously [editor's note: I have found that Sam's Teach Yourself TCP/IP in 24 hours is much better than the 'For Dummies' book]. It still leaves some things to be desired, but nothing to
critical is omitted. It has more than most people will ever care about, and most of it
is
useless to most folks, as the whole thing is highly theoretical. There is no such thing as
the OSI protocol. The OSI Reference model is, well, simply a reference
model.
It is a theoretical outline to guide your networks and to help them operate smoothly. Also
knowing the OSI RM is a nice tool when securing a network (or "un-securing"
it?),
as each layer is dependent upon the layers below it, and depended upon by
the layer above it. i.e. if you can gain control of one layer, that gives
you
control over all the layers below it, and is a starting point to the layer
above it. So not only can it be used as a reference to build the network,
but also a reference to attack it. If you get to layer seven, and it's a
windows 3.X/95/98 box, you've just rooted it. If not, you've rooted it or
are close(er) to rooting it. Somewhere there is a very nice piece on using
the OSI RM in this manner, but I cannot think of it's name offhand. Look
around... I strongly suggest attempting to find weak layers on your box (any
unused servers running?) and trying to exploiting them to the fullest, and
then
patching them to someone else doesn't do it for you someday. An easy way to remember the seven layers is " Phucking Demented Network Topologies Suck
Packets Away " What is a network topology you ask? It's just the physical
layout of the network. Maybe I'll write about networking in general next
issue.

Maybe I will this issue. At that, I think I will, hehe.

Some common networking terms:

datagram - A unit of information that's exchanged; this term is used

interchangeably with the words data packet and network message.

DNS - Domain Name Service; Matches logical names(something.something.something) to IP addresses (xxx.xxx.xxx.xxx).

FTP - File Transfer protocol; Used to transfer files between systems.

NFS - Network File System; Allows one system to mount filesystems from
another system. Originally developed by Sun.

node - A computer on a network.

RIP - Routing Information Protocol; A protocol used by routers to exchange
information.

SMTP - Simple Mail Transfer Protocol; duh.

RFC - Request For Comments; The docs on Internet related stuff, such as
standards, protocols, etc...

RFC's you should read:

RFC791-RFC793, RFC950, RFC1058, RFC1180, RFC1208, and RFC1219. They can be
found at ftp.internic.net/rfc/

Marijuana:

Hey, Techs are (IMOHO) SOPOSED to smoke, but try to keep it away from your
puter's intakes, alright? The tar builds up and can corrode components over
time. Same goes for cigarettes, but, eh. Ciggs are weak, give me the weed.
[editor's note: HITB in no way condones the views expressed in the previous paragraph, get that you narco Feds!]

Places to go for more information:
www.internic.com.
Your local warez book server (yes, people actually serve pirated books...).

(*)It should be noted that NICs operate at both the physical and data link
layers

P.S. This article sucks, I know. I was very busy during the time I had to
write this, and I was lucky I got this much in it. I was hoping to cover
network topologies, but I just didn't have time to write it _and_ get this
turned in on time.

1.) Daemon
processes - psyops
2.)Analysis
: Implications of Internet Growth - CptZZap
3.)The Art of
IRC - JesterS
4.)Network
Stacks & TCP/IP - Liquid Sphear
5.)Basics of
Internet Investigations - madirish
6.)Proliferation of
the Internet
7.)Having fun
with system.ini - xearthed
8.)A look into
VPNs and setting one up - L33tdawg
9.)Review of
DIVA LAN ISDN Router - L33tdawg
10.)Strategies
for Tomorrows War - Cpt ZZap