Transproxy
Transproxy
Transproxy
Welcome to Transparent Proxying
Introduction
The program is used in conjunction with the FreeBSD (ipfw, ipnat) or
Linux transparent proxy feature (ipfwadm, ipchains, iptables), to
transparently proxy HTTP requests.
Where Do I Get It?
The latest version, along with historical versions, of this package
will always be at the follwing URL
with a name like
How Is It Used?
Take for example the network configuration of a FreeBSD or Linux box acting
as a dialin server (or terminal server), and another FreeBSD or Linux box
acting as a Squid (or any other) proxy cache. Normally users would have to
configure their browser to access the proxy. This transparent proxy
will automatically intercept HTTP accesses and re-direct them to the
Squid (or any other) proxy server. The users need not even know that
a proxy is being used, it’s that transparent.
How Do I Build It?
Just type ‘make’ no configuration in the source is needed. It’s
written in ANSI C using the portable Berkeley sockets interface so
it should compile on 99. 9% of machine without change.
How Do I Install It?
Just type ‘make install’ to install the binary and man page. Then
choose either one of ‘Inetd Installation’ or ‘Standalone Server’.
Inetd Installation
For a low volume application, using inetd to start the proxy is very
simple. The installation places the proxy on port 81, just above the
normal HTTP port. Just follow these steps.
Add a line like the following to /etc/services.
tproxy 81/tcp # Transparent Proxy
Add a line like the following to /etc/
tproxy stream tcp nowait nobody /usr/sbin/tcpd tproxy
This tells inetd to accept requests on port 81, and the transparent
proxy server to pass these on to the host ‘proxy’ at port 8080.
Restart the inetd daemon, usually ‘kill -HUP `cat /var/run/`’
does the trick. But check first before running this shell command.
Standalone Server
For high volume applications it’s best to install the server as a standalone
server. This prevents inetd having to start a new process for ever new
request. Just follow these steps.
Find a place to add the server startup to, /etc/rc. d/
or something similar. Add a line like the following to this
file.
tproxy -s 81 -r nobody
This tells the transparent proxy server to accept requests on port
81 and to pass these on to the host ‘proxy’ at port 8080.
The -t option may be given to make the proxy act in a completely
transparent mode. Normal operation is for the proxy
daemon to convert HTTP requests to a form suitable for a Squid
(or any other) proxy cache.
FreeBSD ipfw and ipnat Config
You need FreeBSD 3. 0 or higher, a 2. 2. x doesn’t have the required features.
I suggest you use ipfw as ipnat imposes a much higher overhead.
Add 2 filter entries like below:
# ipfw add 1000 allow tcp from
# ipfw add 1010 fwd
Linux Ipfwadm, Ipchains, Iptables Config
To make HTTP requests get proxied transparently, ipfwadm, ipchains, or
iptables filter rules must be put in place to pass HTTP requests to the
proxy that would normally pass through to the outside world. Also the Linux
kernel must be compiled with the TRANSPARENT_PROXY feature enabled. You
only get asked about this feature if you have requested to be prompted
about EXPERIMENTAL things.
If the dialin server (terminal server) host is not running a d on
port 80, then the ipfwadm, ipchains, or iptables rules are different to when
it is.
Example when a d is running on port 80.
# ipfwadm -I -a accept -P tcp -D localhost 80
# ipfwadm -I -a accept -P tcp -D
# ipfwadm -I -a accept -P tcp -D 0. 0. 0/0 80 -r 81
or
# ipchains -A input -p tcp -d localhost 80 -j ACCEPT
# ipchains -A input -p tcp -d
# ipchains -A input -p tcp -d 0. 0/0 80 -j REDIRECT 81
# iptables -t nat -A PREROUTING -p tcp -d localhost –dport 80 -j ACCEPT
# iptables -t nat -A PREROUTING -p tcp -d / –dport 80 -j ACCEPT
# iptables -t nat -A PREROUTING -p tcp –dport 80 -j REDIRECT –to-port 81
If no d is running on the local network you may want to
reject connections quickly instead of accepting them.
# ipfwadm -I -a reject -P tcp -D localhost 80
# ipfwadm -I -a reject -P tcp -D
# ipchains -A input -p tcp -d localhost 80 -j REJECT
# ipchains -A input -p tcp -d
# iptables -t nat -A PREROUTING -p tcp -d localhost –dport 80 -j REJECT
These rules allow port 80 requests direct at the local network to pass (or
get rejected). Then any requests to the outside world get redirected to
port 81 and hence get handled by the transparent proxy.
Who Am I?
My name is John Saunders <>.
What is a Transparent Proxy | Client vs. Server Side Use Cases
What is a Transparent Proxy
A transparent proxy, also known as an inline proxy, intercepting proxy or forced proxy, is a server that intercepts the connection between an end-user or device and the internet. It is called “transparent” because it does so without modifying requests and responses. Squid Transparent Proxy Server is a popular open source transparent proxy tool.
For example, a user on a corporate network may be surfing the Internet. The user requests to view a news article on, and views the same content as they would on their local connection at home.
However, unbeknownst to the user, the news article is delivered not from the origin server, but rather from a transparent proxy running on the corporate network. The user’s experience is exactly the same. However, the user’s employer now has the ability to monitor their behavior, and also restrict access to certain websites.
Example of a transparent proxy deployment
Transparent Proxies and Forced Proxies
Transparent proxies are sometimes known as forced proxies because they can be applied to a user’s connection without any change to their computer’s proxy settings.
As a result, a transparent proxy can be “forced” on a user without their consent or knowledge (although in many cases users are informed about the presence of a proxy). Some websites maintain unofficial transparent proxy lists, to help users become aware they are monitored.
Transparent proxies, by definition, are set up by the operator of a network or a website, and not by the end-user.
Transparent Proxy Settings
When you set up a transparent proxy, some of the common proxy settings are:
Authentication—provides the server with the same credentials as the users behind the proxy
Interception—defines how the proxy should intercept traffic, at the operating system level or at the router level
Caching—defines whether the proxy server should cache content for returning users
Reverse proxy—you can place the proxy in front of a web server to accelerate performance for users (as opposed to setting it to intercept remote access)
Filtering chat, data streaming, torrent threads, etc—configure the transparent proxy not to allow users to access certain protocols or ports
Uses for Transparent Proxy on Client Side
You can deploy a transparent proxy on the client side, meaning that all traffic to and from a client endpoint is intercepted by the proxy. Use cases for client-side transparent proxies include:
Content Filtering
You can use a transparent proxy to filter out unwanted content, defined via proxy settings. For example, when a specific website is requested, the proxy can refrain from forwarding the request to the web server. Instead, it intercepts the connection and displays an error or notice to the user.
Gateway Proxies
You can use a gateway proxy to modify or block network traffic based on rules. For example, a firewall is a transparent proxy, which allows traffic to pass between an internal network and the Internet, but blocks traffic if it violates the firewall’s rule table.
Transparent Caching
If multiple people are accessing the same content from the same location—for example, many students viewing the same news site via their university network—it is more efficient to initially cache the content, and serve it from cache to subsequent users. A transparent proxy can do this for an organization, facility or neighborhood.
Traffic Monitoring
If you operate a network, you can set up a transparent proxy to monitor user traffic and behavior.
Traffic monitoring can also have illegitimate uses—for example, an unscrupulous public wifi operator can monitor user’s connections and steal data and credentials.
Authentication
Public wifi spots and cellular Internet operators sometimes use transparent proxies to force users to authenticate themselves on the network, and agree to terms of service. Only after a user authenticates and agrees, are they allowed to surf.
Users may not realize that even after the initial authentication screen, the entire connection is intercepted and could be monitored by the operator, via the transparent proxy.
Uses for Transparent Proxy on the Server Side
TCP Intercept for DoS Protection
TCP intercept is a type of transparent proxy which you can use to protect a server against a SYN-flood Denial of Service (DoS) attack. It intercepts all traffic to a web server, accepts client requests, and performs a three-way handshake. If successful, it performs a three-way handshake with the server, and joins the two half-connections between client and server.
The TCP intercept watches TCP requests, and waits (typically 30 seconds) for connections to be established. When the number of inactive connections exceeds a certain threshold, the TCP intercept enters “aggressive mode”. In this mode, each new arriving connection causes the oldest inactive connection to be deleted.
This technique is no longer effective against modern, large scale Distributed Denial of Service (DDoS) attacks. Attackers controlling high-powered servers, or millions of zombie computers, can create SYN floods that easily overwhelm a TCP intercept controller.
This is why many organizations are using cloud-based services like Imperva’s DDoS Protection. Cloud-based DDoS services are able to scale up on-demand to handle large scale attacks, and can also protect against other types of DDoS. For example, DDoS services can prevent protocol attacks and application layer attacks, which do not occur at the TCP layer.
Transparent Proxy and CDN for Front-End Optimization
A Content Delivery Network (CDN) is a globally distributed network of proxy servers, which caches and serves content to users near their geographical location.
A CDN, such as Imperva’s Global Content Delivery Network, is a type of transparent proxy operating on the server side, whose purpose is to perform front-end optimization to improve the end-user experience. It intercepts traffic to a web server and instead of letting the user access the origin server directly, it offers the same content from its cache. This results in improved performance for user and reduced system resources required on the server.
What is a Transparent Proxy? – StackPath Blog
Definition
Transparent proxies are intermediary systems that sit between a user and a content provider. When a user makes a request to a web server, the transparent proxy intercepts the request to perform various actions including caching, redirection and authentication.
Overview
Web proxies work by intercepting a request, modifying the request if necessary, then handling or forwarding the request to its destination. Proxies allow service providers to shape and optimize the way users connect to their services, but they also allow network providers to impact the way users or employees access external resources.
Traditionally, proxies are accessed by configuring the user’s application or network settings. With transparent proxying, the proxy intercepts requests by intercepting packets directed to the destination, making it seem as though the request is handled by the destination itself. This allows service providers to implement proxying without having to reconfigure the user’s computer.
How transparent proxies work
Transparent proxies act as intermediaries between a user and a web service. When a user connects to a service, the transparent proxy intercepts the request before passing it on to the provider. Transparent proxies are considered transparent because the user isn’t aware of them. On the other hand, the servers hosting the service recognize that the proxied traffic is coming from a proxy and not directly from the user.
Use of transparent proxies
Transparent proxies are extremely versatile. The following list contains common examples of how transparent proxies are used.
Proxy caches create copies of the data stored on a server and serve the cached content to users. This reduces the strain on the web service by having the proxy provide the content instead of the service itself.
Filtering proxies prevent access to certain websites or web services. These are commonly implemented by organizations to prevent users from accessing resources that are unrelated or disruptive to the organization.
Gateway proxies modify or block network traffic based on certain rules. Locations that offer public Wi-Fi often implement gateways that require users to register or accept an agreement before they can use the service.
Example of a transparent proxy
A user in a Starbucks coffeehouse wants to connect their laptop to the store’s Wifi network. When the user opens their web browser, they’re connected to a proxy server that manages all of the network’s communications. Since this is a new user, the proxy displays a webpage in the browser asking the user to agree to certain terms and conditions. If the user accepts, then the proxy routes the user’s traffic to the actual destination.
On a larger scale, content delivery networks like MaxCDN are a form of transparent proxying. CDNs provide caching, redundancy, and speed improvements without exposing or modifying the source system. Users believe they’re connecting directly to the service provider, but all of their requests are being handled by the CDN. This is how services like Google, Facebook, and Twitter handle millions of requests with minimal downtime.
Benefits of transparent proxies
Transparent proxies are an unobtrusive way to add features and functionality to a user’s browsing experience.
Enterprises experience greater control over how their customers interact with their services by routing and modifying requests as they come in.
Users interact with web services more easily since their connections are seamlessly and invisibly passed through the proxy, leaving configuration to the service providers.
Conclusion
Transparent proxies shape the way we interact with the web. Whether they’re serving data faster through caching, filtering out unwanted content, or giving businesses more control over their networks, transparent proxies add functionality to the Internet without adding inconvenience.
Frequently Asked Questions about transproxy
What is Transproxy?
A transparent proxy, also known as an inline proxy, intercepting proxy or forced proxy, is a server that intercepts the connection between an end-user or device and the internet. … However, the user’s employer now has the ability to monitor their behavior, and also restrict access to certain websites.
Are transparent proxies good?
Conclusion. Transparent proxies shape the way we interact with the web. Whether they’re serving data faster through caching, filtering out unwanted content, or giving businesses more control over their networks, transparent proxies add functionality to the Internet without adding inconvenience.Jun 10, 2016
How do I make my proxy transparent?
Right-click your service, and select Add Interface -> HTTP or HTTPS to display the appropriate dialog (for example, Configure HTTP Interface). Select the checkbox labeled Transparent Proxy (allow bind to foreign address).
