MANILA, JULY 27, 2011 (STAR) By Rhodina Villanueva - Department of Environment and Natural Resources (DENR) Secretary Ramon Paje has tightened the ban on a number of social networking websites, including Facebook and YouTube, by ordering a software audit of all desktop and laptop computers connected to the department’s central office Internet server.

Paje’s order, contained in Memorandum Circular (MC) No. 2011-06, came after reports reached his office that many DENR employees were able to access the previously banned websites using international proxy servers to bypass firewalls installed by the DENR’s Management Information Systems division.

Through the memorandum circular, Paje also ordered the removal of proxy software.

Last April, Paje issued MC 2011-04 prohibiting the use of Facebook, Twitter, Friendster, Multiply, Meebo, Bebo and other social networking websites, as well as online and offline games, during office hours.

The ban, he said, is meant to “increase productivity in the workplace.”

“Anyone, regardless of employment status, caught using proxy software to access banned sites shall be subjected to Civil Service rules and regulations,” he said.

Paje also tasked Assistant Secretary for Internal Audit and Anti-Corruption Daniel Nicer to take action against employees caught violating his order.

Violation of administrative rules based on civil service laws is punishable by reprimand for the first offense, suspension for the second, and dismissal for third offense.


[PHOTO - Schematic representation of a proxy server, where the computer in the middle acts as the proxy server between the other two.]

In computer networks, a proxy server is a server (a computer system or an application) that acts as an intermediary for requests from clients seeking resources from 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 evaluates the request according to its filtering rules. For example, it may filter traffic by IP address or protocol. If the request is validated by the filter, the proxy provides the resource by connecting to the relevant 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 'caches' responses from the remote server, and returns subsequent requests for the same content directly.

Most proxies are a web proxy, allowing access to content on the World Wide Web.

A proxy server has a large variety of potential purposes, including:

A proxy server that passes requests and responses unmodified is usually called a gateway or sometimes tunneling proxy.

A proxy server can be placed in the user's local computer or at various points between the user and the destination servers on the Internet.

A reverse proxy is (usually) an Internet-facing proxy used as a front-end to control and protect access to a server on a private network, commonly also performing tasks such as load-balancing, authentication, decryption or caching.

A reverse proxy taking requests from the Internet and forwarding them to servers in an internal network. Those making requests connect to the proxy and may not be aware of the internal network. An open proxy forwarding requests from and to anywhere on the Internet. A forward proxy taking requests from an internal network and forwarding them to the Internet.

Types of proxy

Forward proxies: A forward proxy taking requests from an internal network and forwarding them to the Internet. Forward proxies are proxies where the client server names the target server to connect to. Forward proxies are able to retrieve from a wide range of sources (in most cases anywhere on the Internet).

The terms "forward proxy" and "forwarding proxy" are a general description of behaviour (forwarding traffic) and thus ambiguous. Except for Reverse proxy, the types of proxies described on this article are more specialized sub-types of the general forward proxy concept.

Open proxies: An open proxy forwarding requests from and to anywhere on the Internet.Main article: Open proxy An open proxy is a forwarding proxy server that is accessible by any Internet user. Gordon Lyon estimates there are "hundreds of thousands" of open proxies on the Internet. An anonymous open proxy allows users to conceal their IP address while browsing the Web or using other Internet services.

Reverse proxies: A reverse proxy taking requests from the Internet and forwarding them to servers in an internal network. Those making requests connect to the proxy and may not be aware of the internal network. A reverse proxy is a proxy server that appears to clients to be an ordinary server. Requests are forwarded to one or more origin servers which handle the request. The response is returned as if it came directly from the proxy server.

Reverse proxies are installed in the neighborhood of one or more web servers. All traffic coming from the Internet and with a destination of one of the web servers goes through the proxy server. The use of "reverse" originates in its counterpart "forward proxy" since the reverse proxy sits closer to the web server and serves only a restricted set of websites.

There are several reasons for installing reverse proxy servers:

Encryption / SSL acceleration: when secure web sites are created, the SSL encryption is often not done by the web server itself, but by a reverse proxy that is equipped with SSL acceleration hardware. Furthermore, a host can provide a single "SSL proxy" to provide SSL encryption for an arbitrary number of hosts; removing the need for a separate SSL Server Certificate for each host, with the downside that all hosts behind the SSL proxy have to share a common DNS name or IP address for SSL connections.

This problem can partly be overcome by using the SubjectAltName feature of X.509 certificates.

Load balancing: the reverse proxy can distribute the load to several web servers, each web server serving its own application area. In such a case, the reverse proxy may need to rewrite the URLs in each web page (translation from externally known URLs to the internal locations).

Serve/cache static content: A reverse proxy can offload the web servers by caching static content like pictures and other static graphical content.

Compression: the proxy server can optimize and compress the content to speed up the load time.

Spoon feeding: reduces resource usage caused by slow clients on the web servers by caching the content the web server sent and slowly "spoon feeding" it to the client. This especially benefits dynamically generated pages.

Security: the proxy server is an additional layer of defense and can protect against some OS and WebServer specific attacks. However, it does not provide any protection to attacks against the web application or service itself, which is generally considered the larger threat.

Extranet Publishing: a reverse proxy server facing the Internet can be used to communicate to a firewalled server internal to an organization, providing extranet access to some functions while keeping the servers behind the firewalls. If used in this way, security measures should be considered to protect the rest of your infrastructure in case this server is compromised, as its web application is exposed to attack from the Internet.

Gateways to private networksProxy servers can perform a role similar to a network switch in linking two networks.

Accessing services anonymously:

Anonymizer: An anonymous proxy server (sometimes called a web proxy) generally attempts to anonymize web surfing. There are different varieties of anonymizers. The destination server (the server that ultimately satisfies the web request) receives requests from the anonymizing proxy server, and thus does not receive information about the end user's address. However, the requests are not anonymous to the anonymizing proxy server, and so a degree of trust is present between the proxy server and the user. Many of them are funded through a continued advertising link to the user.

Access control: Some proxy servers implement a logon requirement. In large organizations, authorized users must log on to gain access to the web. The organization can thereby track usage to individuals.

Some anonymizing proxy servers may forward data packets with header lines such as HTTP_VIA, HTTP_X_FORWARDED_FOR, or HTTP_FORWARDED, which may reveal the IP address of the client.

Other anonymizing proxy servers, known as elite or high anonymity proxies, only include the REMOTE_ADDR header with the IP address of the proxy server, making it appear that the proxy server is the client.

A website could still suspect a proxy is being used if the client sends packets which include a cookie from a previous visit that did not use the high anonymity proxy server. Clearing cookies, and possibly the cache, would solve this problem.

Implementations of proxies: Web proxyA proxy that focuses on World Wide Web traffic is called a "web proxy". The most common use of a web proxy is to serve as a web cache. Most proxy programs provide a means to deny access to URLs specified in a blacklist, thus providing content filtering. This is often used in a corporate, educational, or library environment, and anywhere else where content filtering is desired. Some web proxies reformat web pages for a specific purpose or audience, such as for cell phones and PDAs.

Suffix proxies: A suffix proxy server allows a user to access web content by appending the name of the proxy server to the URL of the requested content (e.g. ""). Suffix proxy servers are easier to use than regular proxy servers.

Transparent proxies: An intercepting proxy (also forced proxy or transparent proxy) combines a proxy server with a gateway or router (commonly with NAT capabilities). Connections made by client browsers through the gateway are diverted to the proxy without client-side configuration (or often knowledge). Connections may also be diverted from a SOCKS server or other circuit-level proxies.

RFC 2616 (Hypertext Transfer Protocol—HTTP/1.1) offers standard definitions:

"A 'transparent proxy' is a proxy that does not modify the request or response beyond what is required for proxy authentication and identification".

"A 'non-transparent proxy' is a proxy that modifies the request or response in order to provide some added service to the user agent, such as group annotation services, media type transformation, protocol reduction, or anonymity filtering".

A security flaw in the way that transparent proxies operate was published by Robert Auger in 2009 and advisory by the Computer Emergency Response Team was issued listing dozens of affected transparent, and intercepting proxy servers.

Purpose: Intercepting proxies are commonly used in businesses to prevent avoidance of acceptable use policy, and to ease administrative burden, since no client browser configuration is required. This second reason however is mitigated by features such as Active Directory group policy, or DHCP and automatic proxy detection.

Intercepting proxies are also commonly used by ISPs in some countries to save upstream bandwidth and improve customer response times by caching. This is more common in countries where bandwidth is more limited (e.g. island nations) or must be paid for.

Issues: The diversion / interception of a TCP connection creates several issues. Firstly the original destination IP and port must somehow be communicated to the proxy. This is not always possible (e.g. where the gateway and proxy reside on different hosts). There is a class of cross site attacks which depend on certain behaviour of intercepting proxies that do not check or have access to information about the original (intercepted) destination. This problem can be resolved by using an integrated packet-level and application level appliance or software which is then able to communicate this information between the packet handler and the proxy.

Intercepting also creates problems for HTTP authentication, especially connection-oriented authentication such as NTLM, since the client browser believes it is talking to a server rather than a proxy. This can cause problems where an intercepting proxy requires authentication, then the user connects to a site which also requires authentication.

Finally intercepting connections can cause problems for HTTP caches, since some requests and responses become uncacheble by a shared cache.

Therefore intercepting connections is generally discouraged. However due to the simplicity of deploying such systems, they are in widespread use.

Implementation Methods: Interception can be performed using Cisco's WCCP (Web Cache Control Protocol). This proprietary protocol resides on the router and is configured from the cache, allowing the cache to determine what ports and traffic is sent to it via transparent redirection from the router. This redirection can occur in one of two ways: GRE Tunneling (OSI Layer 3) or MAC rewrites (OSI Layer 2).

Once traffic reaches the proxy machine itself interception is commonly performed with NAT (Network Address Translation). Such setups are invisible to the client browser, but leave the proxy visible to the web server and other devices on the internet side of the proxy. Recent Linux and some BSD releases provide TPROXY (transparent proxy) which performs IP-level (OSI Layer 3) transparent interception and spoofing of outbound traffic, hiding the proxy IP address from other network devices.

Detection: There are several methods that can often be used to detect the presence of an intercepting proxy server:

By comparing the client's external IP address to the address seen by an external web server, or sometimes by examining the HTTP headers received by a server.

A number of sites have been created to address this issue, by reporting the user's IP address as seen by the site back to the user in a web page. By comparing the sequence of network hops reported by a tool such as trace route for a proxied protocol such as http (port 80) with that for a non proxied protocol such as SMTP (port 25). By attempting to make a connection to an IP address at which there is known to be no server. The proxy will accept the connection and then attempt to proxy it on. When the proxy finds no server to accept the connection it may return an error message or simply close the connection to the client. This difference in behaviour is simple to detect. For example most web browsers will generate a browser created error page in the case where they cannot connect to an HTTP server but will return a different error in the case where the connection is accepted and then closed. [SOURCE: WIKIPEDIA]

Chief News Editor: Sol Jose Vanzi

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