Proxy server Wikipedia. Communication between two computers shown in grey connected through a third computer shown in red acting as a proxy. Bob does not know to whom the information is going, which is why proxies can be used to protect privacy. 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 and the proxy server evaluates the request as a way to simplify and control its complexity. Proxies were invented to add structure and encapsulation to distributed systems. Today, most proxies are web proxies, facilitating access to content on the World Wide Web, providing anonymity and may be used to bypass IP address blocking. Types of proxy serverseditA proxy server may reside on the users local computer, or at various points between the users computer and destination servers on the Internet. A proxy server that passes unmodified requests and responses is usually called a gateway or sometimes a tunneling proxy. A forward proxy is an Internet facing proxy used to retrieve from a wide range of sources in most cases anywhere on the Internet. A reverse proxy is usually an internal facing proxy used as a front end to control and protect access to a server on a private network. A reverse proxy commonly also performs tasks such as load balancing, authentication, decryption or caching. Open proxiesedit. American Proxy Program' title='American Proxy Program' />An open proxy forwarding requests from and to anywhere on the Internet. 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. There are varying degrees of anonymity however, as well as a number of methods of tricking the client into revealing itself regardless of the proxy being used. Reverse proxiesedit. 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. Programs AZ. Find program websites, online videos and more for your favorite PBS shows. American Proxy Program' title='American Proxy Program' />A reverse proxy or surrogate is a proxy server that appears to clients to be an ordinary server. Reverse proxies forward requests to one or more ordinary servers which handle the request. The response from the proxy server is returned as if it came directly from the original server, leaving the client with no knowledge of the origin servers. 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 neighborhoods 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 Secure Sockets Layer 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. Agatha Christie And Then There Were None Pc Free Download there. This problem can partly be overcome by using the Subject. Alt. Name feature of X. 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. Servecache 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 defence and can protect against some OS and Web Server specific attacks. However, it does not provide any protection from 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 firewall server internal to an organization, providing extranet access to some functions while keeping the servers behind the firewalls. Glass Lewis Proxy Paper research service features casebycase, independent analysis of all the proposals contained in tens of thousands of meetings held each year. Because it is the nations largest educational program, involving virtually all degreeseeking students, general education provides the site and the. 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. Monitoring and filteringeditSecondary market brokerseditNot to be confused with secondary market, secondary market brokers use web proxy servers to buy large stocks of limited products such as limited sneakers5 or tickets. Content control softwareeditA content filtering web proxy server provides administrative control over the content that may be relayed in one or both directions through the proxy. It is commonly used in both commercial and non commercial organizations especially schools to ensure that Internet usage conforms to acceptable use policy. A content filtering proxy will often support user authentication to control web access. It also usually produces logs, either to give detailed information about the URLs accessed by specific users, or to monitor bandwidth usage statistics. It may also communicate to daemon based andor ICAP based antivirus software to provide security against virus and other malware by scanning incoming content in real time before it enters the network. Many work places, schools and colleges restrict the web sites and online services that are accessible and available in their buildings. Governments also censor undesirable content. This is done either with a specialized proxy, called a content filter both commercial and free products are available, or by using a cache extension protocol such as ICAP, that allows plug in extensions to an open caching architecture. Ironically, websites commonly used by students to circumvent filters and access blocked content often include a proxy, from which the user can then access the websites that the filter is trying to block. Requests may be filtered by several methods, such as a URL or DNS blacklists blacklist, URL regex filtering, MIME filtering, or content keyword filtering. Some products have been known to employ content analysis techniques to look for traits commonly used by certain types of content providers. Blacklists are often provided and maintained by web filtering companies, often grouped into categories pornography, gambling, shopping, social networks, etc. Assuming the requested URL is acceptable, the content is then fetched by the proxy. At this point a dynamic filter may be applied on the return path. For example, JPEG files could be blocked based on fleshtone matches, or language filters could dynamically detect unwanted language. If the content is rejected then an HTTP fetch error may be returned to the requester. Most web filtering companies use an internet wide crawling robot that assesses the likelihood that a content is a certain type. The resultant database is then corrected by manual labor based on complaints or known flaws in the content matching algorithms. Some proxies scan outbound content, e. Major Cell Phone Radiation Study Reignites Cancer Questions. Federal scientists released partial findings Friday from a 2. The findings, which chronicle an unprecedented number of rodents subjected to a lifetime of electromagnetic radiation starting in utero, present some of the strongest evidence to date that such exposure is associated with the formation of rare cancers in at least two cell types in the brains and hearts of rats. The results, which were posted on a prepublication Web site run by Cold Spring Harbor Laboratory, are poised to reignite controversy about how such everyday exposure might affect human health. Researchers at the National Toxicology Program NTP, a federal interagency group under the National Institutes of Health, led the study. They chronically exposed rodents to carefully calibrated radio frequency RF radiation levels designed to roughly emulate what humans with heavy cell phone use or exposure could theoretically experience in their daily lives. The animals were placed in specially built chambers that dosed their whole bodies with varying amounts and types of this radiation for approximately nine hours per day throughout their two year life spans. This is by farfar and awaythe most carefully done cell phone bioassay, a biological assessment. This is a classic study that is done for trying to understand cancers in humans, says Christopher Portier, a retired head of the NTP who helped launch the study and still sometimes works for the federal government as a consultant scientist. There will have to be a lot of work after this to assess if it causes problems in humans, but the fact that you can do it in rats will be a big issue. It actually has me concerned, and Im an expert. More than 9. American adults use cell phones. Relatively little is known about their safety, however, because current exposure guidelines are based largely on knowledge about acute injury from thermal effects, not long term, low level exposure. The International Agency for Research on Cancer in 2. RF radiation as a possible human carcinogen. But data from human studies has been inconsistent, the NTP has said on its website. Such studies are also hampered by the realities of testing in humans, such as recall biasmeaning cancer patients have to try to remember their cell phone use from years before, and how they held their handsets. Those data gaps prompted the NTP to engage in planning these new animal studies back in 2. The researchers found that as the thousands of rats in the new study were exposed to greater intensities of RF radiation, more of them developed rare forms of brain and heart cancer that could not be easily explained away, exhibiting a direct doseresponse relationship. Overall, the incidence of these rare tumors was still relatively low, which would be expected with rare tumors in general, but the incidence grew with greater levels of exposure to the radiation. Some of the rats had gliomaa tumor of the glial cells in the brainor schwannoma of the heart. Furthering concern about the findings In prior epidemiological studies of humans and cell phone exposure, both types of tumors have also cropped up as associations. In contrast, none of the control ratsthose not exposed to the radiationdeveloped such tumors. But complicating matters was the fact that the findings were mixed across sexes More such lesions were found in male rats than in female rats. The tumors in the male rats are considered likely the result of whole body exposure to this radiation, the study authors wrote. And the data suggests the relationship was strongest between the RF exposure and the lesions in the heart, rather than the brain Cardiac schwannomas were observed in male rats at all exposed groups, the authors note. But no biologically significant effects were observed in the brain or heart of female rats regardless of modulation. Based on these findings, Portier said that this is not just an associated findingbut that the relationship between radiation exposure and cancer is clear. I would call it a causative study, absolutely. They controlled everything in the study. Its the cancer because of the exposure. Earlier studies had never found that this type of radiation was associated with the formation of these cancers in animals at all. But none of those studies followed as many animals, for as long or with the same larger intensity exposures, says Ron Melnick, a scientist who helped design the study and is now retired from the NTP. The new results, published on Web site bio. RXiv, involved experiments on multiple groups of 9. The study was designed to give scientists a better sense of the magnitude of exposure that would be associated with cancer in rodents. In the study rats were exposed to RF at 9. There were three test groups with each species of each sex, tested at different radiation intensities 1. Wkg, and one control group. The lowest intensity level roughly approximates the levels allowed by U. S. cell phone companies, which is 1. Wkg. There are only 9. Probably what caused cancer at the high doses will cause cancer at lower doses but to a lesser degree, Portier says. Rodents across all the test groups were chronically exposed to RF for approximately nine hours spread out over the course of the day. Their entire bodies were exposed because people are exposed to such radiation beyond their heads, especially when they carry them or store them in their bras, says John Bucher, the associate director of the NTP. During the study the rats were able to run around in their cages, and to eat and sleep as usual. Free Program Za Urejanje Slik Programs on this page. The experiments also included both types of modulations emitted from todays cell phones Code Division Multiple Access and Global System for Mobile. Modulations are the way the information is carried, so although the total radiation levels were roughly the same across both types, there were differences in how radiation is emitted from the antennaeither a higher exposure for a relatively short time or a lower exposure for a longer time. Overall, there was no statistically significant difference between the number of tumors that developed in the animals exposed to CDMA versus GSM modulations. With both modulations and tumor types, there was also a statistically significant trend upwardmeaning the incidence increased with more radiation exposure. Yet, drilling down into the data, in the male rats exposed to GSM modulated RF radiation the number of brain tumors at all levels of exposure was not statistically different than in control malesthose who had no exposure at all. The trend here is important. The question is, Should one be concerned The answer is clearly Yes. But it raises a number of questions that couldnt be fully answered, says David Carpenter, a public health clinician and the director of the Institute for Health and the Environment at the University at Albany, S. U. N. Y. The findings are not definitive, and there were other confusing findings that scientists cannot explainincluding that male rats exposed to the radiation seemed to live longer than those in the control group. Overall we feel that the tumors are likely related to the exposures, says Bucher, but such unanswered questions have been the subject of very intense discussions here. The NTP released the partial findings on Friday after an online publication called Microwave News reported them earlier this week. The program will still be putting out other results about the work in rats and additional findings about similar testing conducted in mice. The NIH told Scientific American in a statement, This study in mice and rats is under review by additional experts.
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