A proxy server acts as an intermediary between a client and an external server. When a client makes a request, the proxy server connects to the target server on the client's behalf and returns the information to the client. Proxy servers can cache responses to improve speed for subsequent identical requests from clients. They are often used within corporate networks to filter traffic and protect internal networks from unauthorized external access. However, using an untrusted proxy server poses risks as it can record unencrypted login credentials and browsing activity passing through it.

1. How Corporate
Firewalls Work
week14 WEB POSTER
group E
January 22, 2008

2. proxy server
Proxy Server (Proxy Server) is a substitute meaning, and it is a
representation server serving as interagency with a client and the objective
server.
When a client PC connects with the Internet, I receive an access demand,
and Proxy Server connects with a target server in the Internet as substitution
of the client, and it is the server which it carried a function to return the
information to a client on. It is installed on the inside (the LAN side) of a
physical firewall or a firewall in a company network and accesses a Web
server (or, server) of the Internet.
Proxy Server manages the Internet connection of the client PC 1 yuan
and admits connection, and it is used by unjust access from the outside to
protect an internal network. Sake to save information (data) that I reply to a
client PC as a merit with Proxy Server and am connected and acquired on a
physics disk of Proxy Server (I do cash), plural client PCs can contribute to
improvement of the speed of the Internet connection cash forwards a done
file, and to reply when I carried out the same access demand.

3. Proxy Server
In computer networks, a proxy server is a server which services the requests of its clients by
forwarding requests to other servers. A client connects to the proxy server, requesting some service,
such as a file, connection, web page, or other resource, available from a different server. The proxy
server provides the resource by connecting to the specified server and requesting the service on behalf
of the client. A proxy server may optionally alter the client's request or the server's response, and
sometimes it may serve the request without contacting the specified server. In this case, it would
'cache' the first request to the remote server, so it could save the information for later, and make
everything as fast as possible. A proxy server that passes all requests and replies unmodified is
usually called a gateway or sometimes tunneling proxy .A proxy server can be placed in the user's
local computer or at specific key points between the user and the destination servers or the Internet.
Risks
In using a proxy server, all data sent to the service being used must pass through the proxy server
before being sent to the service, mostly in unencrypted form. It is therefore possible, and has been
demonstrated, for a malicious proxy server to record everything sent to the proxy: including
unencrypted login and passwords.
By chaining proxies which do not reveal data about the original requester, it is possible to obfuscate
activities from the eyes of the user's destination. However, more traces will be left on the intermediate
hops, which could be used or offered up to trace the user's activities. If the policies and administrators
of these other proxies are unknown, the user may fall victim to a false sense of security just because
those details are out of sight and mind.
The bottom line of this is to be wary when using proxy servers, and only use proxy servers of known
integrity, and never use proxy servers of unknown integrity. If there is no choice but to use unknown
proxy servers, do not pass any private information through the proxy.
In what is more of an inconvenience than a risk, proxy users may find themselves being blocked from
certain Web sites, as numerous forums and Web sites block IP addresses from proxies known to have
spammed or trolled the site.

4. FTP
File Transfer Protocol (The file transfer protocol and abbreviation: FTP) is a c
ommunications protocol (protocol) to forward the file on the network.
In the protocol that exists since the Internet initial, it is one of the protoco
ls often still used by the Internet. On the protocol, it is usually used for for
warding between the client and the server connecting it though the file transfer
warding between the client and the server connecting it though the file transfer
between arbitrary hosts can be done.
Anonymous (anonymity) FTP server that can be accessed by anonymity might be used
to distribute the file (chiefly free, free software etc.) entirely though the a
ttestation is needed when connecting to the server usually. However, an anonymou
s access is necessary the attestation on the form, and, in this case, specifies
"Anonymous" or "Ftp" for a user. The password is usually good, and anything it h
as been made the specification of user's E-mail address for the server manager t
o contact when there is a wound in the distributed software manners (Withershins
, when it is clear, the domain in the mail address omits the domain from the pul
l etc. about Internet Protocol address of the client like "Foo@"). If the passwo
rd doesn't fill the form of the mail address according to the server, it is not
likely to be able to use it.

5. What is protocol?
In the communication of the computer mutually by the network,
they are sets of promised things decided mutually. It might be
called the communication procedure and the communications
protocol, etc.
It is possible to think dividing into two hierarchies which language
use when man communicates mutually, and transmitted by using
what kind of medium, and it thinks in the computer
communication dividing the role of the protocol into two or more
communications protocol, etc.
It is possible to think dividing into two hierarchies which language
use when man communicates mutually, and transmitted by using
what kind of medium, and it thinks in the computer
communication dividing the role of the protocol into two or more
hierarchies.it doesn't worry whether stay up of what in the under
from it at all and a high-ranking protocol (software that mounts)
can be communicated by hierarchizing it if it knows.

6. Firewalls Work
Firewalls make it possible to filter incoming and outgoing traffic that flows through your system. A
firewall can use one or more sets of “rules” to inspect the network packets as they come in or go out
of your network connections and either allows the traffic through or blocks it. The rules of a firewall
can inspect one or more characteristics of the packets, including but not limited to the protocol type,
the source or destination host address, and the source or destination port.
There are several classifications of firewalls depending on where the communication is taking place,
where the communication is intercepted and the state that is being traced.
*Network layer and packet filters,
*Application-layer,
*Proxies,
*Network address translation
REFERENCE
http://srd.yahoo.co.jp/IMG/r=1/ig=465x342/id=94894e2710642f4c/l=ri/da=g/tid=MMSI02_01/q=pro
xy%20server/SIG=11r2hkuao/EXP=1200987756/*-http%3A//www.inode.gr/img/proxy_small.jpg
http://ja.wikipedia.org/wiki/%E3%83%97%E3%83%AD%E3%82%AD%E3%82%B7
http://www.secomtrust.net/secword/proxyserver.html
http://img.zdnet.com/techDirectory/LAN2.GIF
http://ja.wikipedia.org/wiki/File_Transfer_Protocol
http://www.jnutella.org/docs/gnutella/Firewalls.html
http://www.freebsd.org/doc/en_US.ISO8859-1/books/handbook/firewalls.html

7. http://e-words.jp/w/FTP.html