
U S E R S
User Guide |
ComSifter CS-8D Pro
6–15
Understanding and Determining Transparent and Proxy Modes
When initially configuring your ComSifter it is important to understand the concepts of transparent and proxy
modes.
Background information
Unlike a router, that only has to pass packets to and from the LAN to the Internet. The ComSifter must retrieve
all of a page. The page you view in your browser consists of many connects (as few as two, as many as a few
hundred). The connects are assembled by the browser and presented to you as a finished page. The
ComSifter cannot display any of the page until it has all of the page—as the last connect could be, or could
point to, objectionable content.
When the ComSifter is retrieving a page from a website, it is doing so as a result of a request from a client
computer. When doing this, the ComSifter is acting as a proxy for the client computer making the request. It is
at this point where the differences between transparent and proxy mode become important.
Transparent Mode
In transparent mode, the browser makes a request to retrieve a page from a web site. This request is made
using the HTTP protocol and is made using standard port 80. The ComSifter intercepts this request and
retrieves the page from the website, applies the appropriate filter rules, and then gives the requesting computer
the complete page (or a denied page). All of this is done transparently, and requires no special configuration of
the browser.
In most cases, this procedure works as expected—but there are instances when it will fail. Some websites
have instituted very strict man-in-the-middle detection schemes. Typically, these sites are involved with secure
(HTTPS) transactions with the client computer and they must protect themselves from man-in-the-middle fraud
schemes. In certain instances, the security schemes of these sites determine that the ComSifter is a man-in-
the-middle and refuse to complete the transaction.
Additionally, if a client program uses a non-standard port (not port 80) and encrypts the transmission (HTTPS)
the ComSifter is unable to see the data and apply filtering rules. The real world result of this is users are able
to try adding an “s” to the protocol (HTTPS) to see if the web site has a secure server. If so, this will circumvent
the filter.
Pros
Does not require any browser configuration.
Cons
HTTPS transactions may fail as the ComSifter may be seen as a man-in the- middle.
Encrypted traffic may be used to access web sites. The ComSifter is not able to see the data.
Proxy Mode
All modern browsers (Internet Explorer, Firefox, Safari, etc) have a proxy mode. In this mode, the browser
changes how it makes a request for a web page. Devices in the path to the web site (such as the ComSifter)
are then able to identify themselves to the website as a proxy and are acting at the request of the client
computer. Websites see this as a legitimate request and allow secure transactions to complete (that may have
failed in transparent mode). Proxy operation is typically more robust than transparent mode, but does require
the extra step of changing the browser to proxy mode. (This is mitigated if the network is part of a domain and
under control of Active Directory Group Policies. Proxy mode may be easily set up under group policies.)
An added benefit of proxy mode is that it gives network administrators much more control over what goes out
to the Internet. In transparent mode, all ports are active and available for use by the client computer (64,000
ports). If a client program uses a non-standard port (not port 80), and encrypts the transmission (HTTPS), the
ComSifter is unable to see the data and apply filtering rules. In proxy mode, all client requests are made over
port 8080. The client asks for both a “connect” to the website, and requests a port number. This is all done in
the clear (not encrypted). The ComSifter is then able to see the requested website and determine if it is on a
Содержание CS-8D Pro
Страница 1: ...ComSifter protect web users now User Guide Model CS 8D Pro Version March 26 2012 0326121500 ...
Страница 153: ...F I L T E R S E T U P User Guide ComSifter CS 8D Pro 4 23 Figure 4 19 Modify Page RegEx ...
Страница 178: ...U S E R S User Guide ComSifter CS 8D Pro 6 12 User Management Utilities Figure 6 14 User List Management ...
Страница 194: ...U S E R S User Guide ComSifter CS 8D Pro 6 28 Figure 6 19 Windows Firewall ...
Страница 215: ...U S E R S User Guide ComSifter CS 8D Pro 6 49 Figure 6 40 Add User ...
Страница 219: ...U S E R S User Guide ComSifter CS 8D Pro 6 53 Figure 6 43 Add IP ...
Страница 227: ...U S E R S User Guide ComSifter CS 8D Pro 6 61 Figure 6 51 Delete a Domain URL to the Client Program Application Bypass ...
Страница 229: ...U S E R S User Guide ComSifter CS 8D Pro 6 63 Figure 6 53 Turning off Merge with Comsift Maintained Bypass List ...
Страница 231: ...U S E R S User Guide ComSifter CS 8D Pro 6 65 Figure 6 55 Turning off Merge with Exception Domain List ...