Basic Networking Tutorial Pt.2

Well I start my vacation on Friday. So here is the second part to my series on netwotking before I go. It is continued from this thread:
http://www.antionline.com/showthread...hreadid=220125
I hope this helps some of you.
Subject of this tut is TCP/IP in networks.

Basic TCP/IP, an understanding__
The TCP/IP protocol suite is named for two of its most
important protocols: Transmission Control Protocol (TCP)
and Internet Protocol (IP). Another name for it is the
Internet Protocol Suite, and this is the phrase used in
official Internet standards documents. We shall use the
more common term TCP/IP to refer to the entire protocol.
The first design goal of TCP/IP was to build an
interconnection of networks that provided universal
communication services: an internet. Each physical network
has its own technology-dependent communication interface,
in the form of a programming interface that provides basic
communication functions (primitives). Communication
services are provided by software that runs between the
physical network and the user applications and that
provides a common interface for these applications,
independent of the underlying physical network. The
architecture of the physical networks is hidden from the
user.
The second aim is to interconnect different physical
networks to form what appears to the the user to be one
large network. Such a set of interconnected networks is
called an internet.
To be able to interconnect two networks, we need a
computer that is attached to both networks and that can
forward packets from one network to the other; such a
machine is called a router. The term IP router is also
used because the routing function is part of the IP layer
of the TCP/IP protocol suite.

The basic properties of a router are:
From the network standpoint, a router is a normal host.
From the user standpoint, routers are invisible. The user
sees only one large internetwork.
To be able to identify a host on the internetwork, each
host is assigned an address, the IP address. When a host
has multiple network adapters, each adapter has a separate
IP address. The IP address consists of two parts:
IP address = <network number><host number>
The network number part of the IP address is assigned by a
central authority and is unique throughout the Internet.
The authority for assigning the host number part of the IP
address resides with the organization which controls the
network identified by the network number.
TCP/IP, like most networking software, is modelled in
layers. This layered representation leads to the term
protocol stack which is synonymous with protocol suite. It
can be used for situating (but not for comparing
functionally) the TCP/IP protocol suite against others,
such as SNA and Open System Interconnection (OSI).
Functional comparisons cannot easily be extracted from
this, as there are basic differences in the layered models
used by the four different protocol suites.

Application ***
is a user process cooperating with another process on the
same or a different host. Examples are TELNET (a protocol
for remote terminal connections), FTP (File Transfer
Protocol) and SMTP (Simple Mail Transfer Protocol). These
are discussed in detail in Application Protocols.
Transport ***
provides the end-to-end data transfer. Example protocols
are TCP (connection-oriented) and UDP (connectionless).
Internet ***
also called the internet layer or the network layer, the
internet provides the ``virtual network'' image of
internet (that is, this layer shields the higher levels
from the typical network architecture below it). Internet
Protocol (IP) is the most important protocol in this
layer. It is a connectionless protocol which doesn't
assume reliability from the lower layers. IP does not
provide reliability, flow control or error recovery. These
functions must be provided at a higher level, either at
the Transport layer by using TCP as the transport
protocol, or at the Application layer if UDP is used as
the transport protocol. IP is discussed in detail in
Internet Protocol (IP). A message unit in an IP network is
called an IP datagram. This is the basic unit of
information transmitted across TCP/IP networks.
Network Interface ***
also called the link layer or the data-link layer, the
network interface layer is the interface to the actual
network hardware. This interface may or may not provide
reliable delivery, and may be packet or stream oriented.
In fact, TCP/IP does not specify any protocol here, but
can use almost any network interface available, which
illustrates the flexibility of the IP layer. Examples are
IEEE 802.2, X.25 and ATM.

Bridges, Routers and Gateways In TCP/IP
Forming an internet by interconnecting multiple networks
is done by routers. It is important to distinguish between
a router, a bridge and a gateway.

Bridge
Interconnects LAN segments at the Network Interface layer
level and forwards frames between them. A bridge performs
the function of a MAC relay, and is independent of any
higher layer protocol. It provides MAC layer protocol
conversion, if required. A bridge can be said to be
transparent to IP. That is, when a host sends an IP
datagram to another host on a network connected by a
bridge, it sends the datagram directly to the host and the
datagram ``crosses'' the bridge without the sending host
being aware of it.
Router
Interconnects networks at the internetwork layer level and
routes packets between them. The router must understand
the addressing structure associated with the networking
protocols it supports and take decisions on whether, or
how, to forward packets. Routers are able to select the
best transmission paths and optimal packet sizes. The
basic routing function is implemented in the IP layer of
the TCP/IP protocol stack. Therefore any host or
workstation running TCP/IP may be used as a router.Because
IP provides this basic routing function, the term ``IP
router'', is often used. Other, older, terms for router
are ``IP gateway'', ``Internet gateway'' and ``gateway''.
The term gateway is now normally used for connections at a
higher level than the router level. A router can be said
to be visible to IP. That is, when a host sends an IP
datagram to another host on a network connected by a
router, it sends the datagram to the router and not
directly to the target host.

Gateway
Interconnects networks at higher levels than bridges or
routers. A gateway usually supports address mapping from
one network to another, and may also provide
transformation of the data between the environments to
support end-to-end application connectivity. Gateways
typically limit the interconnectivity of two networks to a
subset of the application protocols supported on either
one. For example, a VM host running TCP/IP may be used as
an SMTP/RSCS mail gateway. Note: The term ``gateway'',
when used in this sense, is not synonymous with ``IP
gateway''. A gateway can be said to be opaque to IP. That
is, a host cannot send an IP datagram through a gateway:
it can only send it to a gateway. The higher-level
protocol information carried by the datagrams is then
passed on by the gateway using whatever networking
architecture is used on the other side of the gateway.

Closely related to routers and gateways is the concept of
a firewall or firewall gateway which is used to restrict
access from the Internet to a network or a group of
networks controlled by an organization for security
reasons.

IP Routing
Incoming datagrams will be checked to see if the local
host is the IP destination host:
yes
The datagram is passed to the higher-level protocols.
no
The datagram is for a different host. The action depends

on the value of the ipforwarding flag.
true
The datagram is treated as an outgoing datagram and is
routed to the next hop according to the algorithm
described below.
false
The datagram is discarded.
In the internet protocol, outgoing IP datagrams pass
through the IP routing algorithm which determines where to
send the datagram according to the destination IP address.
If the host has an entry in its IP routing table which
matches the destination IP address, the datagram is sent
to the address in the entry. If the network number of the
destination IP address is the same as the network number
for one of the host's network adapters (that is, the
destination and the host are on the same network) the
datagram is sent to the physical address of the host
matching the destination IP address. Otherwise, the
datagram is sent to a default router. This base algorithm,
needed on all IP implementations, is sufficient to perform
the base routing function.
As noted above, a TCP/IP host has basicrouter
functionality included in the IP protocol. Such a router
is adequate for simple routing, but notforcomplex
networks. The IP routing mechanism is combined with the
"layered'' view of the TCP/IP protocol stack. This shows
an IP datagram, going from one IP address (network number
X, host number A) to another (network number Y, host
number B), through two physical networks. Note that at the
intermediate router, only the lower part of the TCP/IP
protocol stack (the internetwork and the network interface
layers) are involved.

Forgot to add. The next part (3) will deal with specific hardware devices and interfaces. I should have it out in the next couple of weeks.

lol nice tut!! ermm just need a little work on your white space coordination to make it pleasant to read ;)

but u get greenies for that :)