Proxy Servers – CompTIA Network+ N10-006 – 1.3

A proxy server is
a device that sits in the middle of
the communication and makes the
request for us, thus the name proxy when we
talk about a proxy server. Our client workstation
would communicate to a proxy– maybe request a
website– the proxy then goes to the website, receives the
response from that website and then sends that information
back to the client device. We are never talking
directly to that end website. The proxy is sitting
in the middle, and it’s performing all
of those communications. We commonly see proxy
servers used for something like control or security. Maybe you need to log in to
gain access to the internet. You’re really
logging into a proxy to provide that access control. Proxies are also
good for caching. So the proxy can
grab information from the internet, and
the second person who needs that information can
grab it from that local cache. You also see this
when you’re doing URL filtering or content
scanning, because the proxy can make the request,
receive the response, and then examine that
information before sending it to the client. So if the client unknowingly
is downloading a file with malware, it could
be scanned at the proxy. And the proxy can throw
that out before it ever reaches the end station. In the example I just
gave, we commonly see a forward proxy being
used to perform that function. This is usually where we’d
have an internal network. And the internal network has,
in this case, a user and a proxy that’s on the inside of
our network and something that is controlled by our
network team or our security team. The end user makes the
request to the internet. It hits the proxy. The proxy then makes the request
directly out to the internet and gets the response. And then once the proxy is
sure that everything is OK, it sends that information
down to the user. Now let’s take that
scenario and reverse it. Instead now you are
on the internet, and you need to access
a web server that’s located on the inside
of an organization. So here we are out
on the internet, and we’re going to communicate
with a reverse proxy. This reverse proxy takes
all of the communications from the internet,
examines it, makes sure there’s nothing that would
be attacking the web server, sends the request down
to the web server. The web server responds,
but of course it’s not responding back to you. It’s responding
back to the proxy. And then the proxy of course
is communicating back to you on the internet. So it’s the same as
the original proxy we were looking at–
our forward proxy– except now we’ve
turned it around and made it a reverse proxy. Another type of proxy you might
run into is an open proxy. We commonly see
open proxies used if you’re trying
to remain anonymous or you’re trying to circumvent
some existing security controls. This is because you’re making
all of your communication to that open proxy. And the open proxy
is then making all of the requests for you
wherever they happen to go. They can go to It could be making
a request to Google. It could be making requests
to Yahoo or any other site you’d like to go to. From your perspective,
you’re communicating to a single device. And that’s how you’re
able to circumvent a number of different
security controls that are looking
for an end station that you might be
communicating with. And by using this proxy, you’re
able to communicate and remain anonymous, because the end
stations can’t see your IP address because it’s
the proxy that’s actually making that request. You do have to be
very careful when using an open proxy of
course, because whoever’s controlling the open
proxy can control exactly what is sent down to you. This makes it very easy for
pop ups, malicious software, and vulnerabilities to be
sent down to your device. So whenever you’re taking
advantage of an open proxy, it’s always useful to know
exactly who owns the proxy and how it’s being administered.