What is a proxy server, and how does it work?

Proxy servers can secure and improve the communication between the client and the requested service. Still, the exact functionality and security or privacy benefits vary depending on your needs and proxy server type.

The word “proxy” means “to act on behalf of another,” and that is precisely what a proxy server does. It acts on the client’s or web server’s behalf to receive and forward requests.

Internet traffic flows through the proxy server on its way to the requested address, and the request then comes back through that same proxy server before you receive the requested data. Here’s how it works in more detail:

1. The client (your device or web browser) requests web content or service from a destination server.
2. Instead of directly contacting the destination server, the request goes to the proxy server first.
3. The proxy server checks whether the client’s request follows predefined rules.
   • If it does, the proxy server forwards the request to the destination server on the client’s behalf.
   • If it doesn’t, the proxy server may show the client an error message or redirect it to another server.
4. The destination server processes the request and responds to the proxy server.
5. The proxy server can make changes to the response. For example, it can cache it for future use, filter it to remove unwanted content, or require authentication before the client can see it.
6. Finally, the proxy server sends the (modified) response to the client. The client sees the web content or uses the service as if it is connected to the destination server directly.

Proxy servers work in a similar way as virtual private network (VPN) servers. They also route traffic on your behalf, masking your identity. The most notable difference between a proxy and a VPN is that VPN also encrypts the traffic while proxy servers don’t.

Since a proxy server can be on the server side or a part of network infrastructure, the client can also be unaware of the intermediary proxy and assume it’s directly communicating with the requested address.

For example, your work network or internet service provider (ISP) can use a proxy server to filter or cache content or even track your activities without you even knowing about it. And those are not the only uses of proxy servers.

Proxies are powerful tools for managing or securing network traffic and improving performance. Here are some of the most common use cases of proxy servers:

• Network filtering. You can use proxy servers to filter and block access to certain websites or web content. In this case, proxies are like firewalls, enforcing compliance and internet censorship, preventing malware infection or phishing attacks, or restricting access to inappropriate or illegal content.
• Caching. Proxy servers store frequently accessed resources like web pages, images, and videos. They then serve cached data to clients instead of fetching content from the original server.
• Load balancing. Proxy servers distribute client requests across multiple servers to prevent overloading one server. They can also detect and redirect requests from failed or overloaded servers to servers that haven’t reached capacity.
• Bypassing restrictions. While proxy servers on the server side can enforce internet restrictions, proxies on the client side can help bypass them. Since proxy servers reroute web traffic, they can bypass restrictions set by network administrators, ISPs, or even governments. Some providers even offer services such as proxies for YouTube, although, techically, such a thing does not exist.
• Masking the IP address. The proxy server connects to the web on your behalf, so the web destination sees the server’s IP address instead of yours. It keeps your IP address and other identifying information hidden from the websites you access online.
• Providing SSL encryption and decryption. Some proxy server types can handle SSL/TLS encryption and decryption. It allows the web server to focus on processing requests rather than dealing with cryptography.
• Routing. A proxy server can route requests through different servers based on predefined criteria, such as the request’s content or the client’s location.

Proxy servers can be categorized in several ways based on their functionality and protocols. Here we’ll take a look at the most common proxy server types.

The most common proxy server classification considers the direction of the traffic flow and the location of the proxy in relation to the client and server. It separates proxy servers into forward and reverse proxies.

Forward proxy

A forward proxy is a proxy server acting on behalf of the client to request resources from the internet. The forward proxy is located on the client’s network, so it’s also known as a client-side proxy.

The internet sees the forward proxy as the client, while the client sees the forward proxy as the internet. Forward proxies hide the client’s IP address and identity, help bypass content filters, and access restricted websites.

Reverse proxy

A reverse proxy is a proxy server acting on behalf of the web server to receive requests from clients. Since a reverse proxy is located on the server’s network, it’s also called a server-side proxy.

The web server sees the reverse proxy as the client, while the client sees the reverse proxy as the web server. A proxy server helps the web server remain hidden from clients, playing a critical role in ensuring the reliability, security, and performance of web applications.

Servers can use reverse proxies for load balancing, caching, and security. Reverse proxies can also provide a single access point to multiple web servers, making managing and scaling web applications easier.

The 502 bad gateway error can appear when the reverse proxy fails to communicate with the server.

Another way to classify proxy servers is based on their location and operators.

Residential proxy

A residential proxy is an intermediary server with an IP address assigned by an internet service provider (ISP) to a homeowner or a business.

Your computer could work as a residential proxy if you let someone outside your household route traffic through it. In that case, you’d be the operator of the residential proxy, and it would have the IP address of your device.

A residential proxy uses include web scraping, data mining, ad verification, and other online activities that require high anonymity and IP rotation. Since residential proxies resemble the behavior of human internet users, websites and search engines usually trust them more than other proxy types. However, getting and maintaining such proxies is also more expensive.

Data center proxy

A data center proxy is an intermediary server hosted in a data center and is usually set up specifically for proxying web traffic. Its uses include high-volume web scraping and automation tasks.

Data center proxies are much easier and cheaper to get and maintain than residential proxies. They’re also more stable and faster, but their behavior is somewhat predictable, so websites and search engines are better at detecting and blocking them.

Mobile proxy

A mobile proxy is an intermediary server hosted on a mobile device, such as a smartphone or tablet, and has the IP address assigned by a mobile carrier. The mobile proxy uses include mobile app testing and mobile ad verification.

Using a proxy server can make your browsing more private, but the level of anonymity differs depending on the proxy server type.

Transparent proxy

A transparent proxy is an intermediary server that doesn’t hide the client’s IP address.

Transparent proxies don’t provide anonymity. They reveal your identity to the server, making them useless for increasing privacy online. However, they exist for a reason. You can use transparent proxies for caching to speed up your web browsing.

Level of anonymity: lowest.

Anonymous proxy

An anonymous proxy is an intermediary server that hides the user’s IP address from web servers. But the anonymous proxy can reveal other information, such as the client’s browser type, language settings, or operating system. While this information doesn’t identify you directly, it helps narrow the pool of potential users.

Level of anonymity: medium.

High anonymity proxy

A high anonymity proxy server is an intermediary that hides the user’s IP address and other identifying information sent in the HTTP headers, such as browser type or operating system.

High anonymity proxies make it more difficult to trace your activities to your IP address or device. As far as proxies go, it’s a decent choice for activities that require privacy.

Level of anonymity: highest.

Distorting proxy

A distorting proxy is an intermediary server that hides the client’s IP address and provides a false IP address to the server.

Level of anonymity: medium to high (depends on the proxy server’s configuration).

Rotating proxy

A rotating proxy is an intermediary server that uses a pool of IP addresses and rotates them periodically to provide anonymity and prevent IP blocking.

Rotating proxies can help with web scraping, data mining, and other activities requiring many requests to be sent to a server without being detected.

Level of anonymity: medium to high (depends on the number of IP addresses in the pool and how often they are rotated).

Accessibility is another way to separate proxies into different categories.

Public proxy

A public proxy is a proxy server open to anyone. You can access it without needing to pass authentication, just like an open proxy. Naturally, such accessibility makes public proxies slower and less reliable. They have the highest risk of being blocklisted and blocked by websites and search engines.

Shared proxy

A shared proxy is a proxy server used by many users. They share the same IP address and port, but their online activities are kept separate through various software and hardware configurations. It’s also called a semi-dedicated proxy.

Shared proxies are not public, so they require authentication to access. It makes them faster and more reliable than public proxies.

Private proxy

A private proxy is a proxy server only used by a single user or organization. Private proxies provide a dedicated IP address and port to the user, so they’re also called dedicated proxies.

Private proxies offer a higher level of privacy, security, and performance. They require authentication to access and cost more than shared proxies.

Some proxy servers handle traffic from specific network protocols or types of traffic. So their traffic type and protocols help to divide them.

HTTP proxy

An HTTP (Hypertext Transfer Protocol) proxy is a web proxy server that handles HTTP requests between clients and servers on the internet.

HTTP proxies are great for caching because they can store a copy of web content. They can filter content and hide the client’s IP address from the server. But since they handle plain-text requests, they are not the best choice for sensitive data.

HTTPS proxy

An HTTPS (Hypertext Transfer Protocol Secure) proxy is a web proxy server that handles HTTPS traffic between clients and servers on the internet.

An HTTPS proxy works similarly to an HTTP proxy, except your connection to the proxy server is encrypted. And since HTTPS proxies handle encrypted traffic, they cannot see or cache it.

SSL proxy

An SSL (Secure Sockets Layer) proxy is a proxy server that handles SSL traffic between clients and servers on the internet.

An SSL proxy can decrypt and inspect the traffic for security purposes, such as detecting and blocking malicious traffic or ensuring that only authorized users can access certain websites through SSL inspection.

SMTP proxy

An SMTP (Simple Mail Transfer Protocol) proxy is a proxy server that handles SMTP traffic between email clients and servers.

You can use SMTP proxies to send and receive emails securely because they can scan incoming and outgoing email messages for spam and malware. They can also help optimize email traffic by caching frequently accessed email messages and attachments.

FTP proxy

An FTP (File Transfer Protocol) proxy is a proxy server that handles FTP traffic between clients and servers. This protocol, and thus the proxies handling it, are responsible for file transferring over the internet.

FTP proxies provide security and control over the FTP traffic by filtering or modifying it. For example, they can limit the file types or sizes.

DHCP proxy

A DHCP (Dynamic Host Configuration Protocol) proxy is a proxy server that handles DHCP requests and responses between DHCP clients and servers on different network segments.

DHCP requests help obtain IP addresses and other network configuration parameters. So DHCP proxies usually operate at the network layer, and primarily large networks use them for IP address allocation.

DNS proxy

A DNS (Domain Name System) proxy is a proxy server that handles DNS requests from clients. A DNS proxy intercepts the DNS queries from the client and forwards them to the appropriate DNS server.

DNS proxies can filter or modify the DNS traffic to block access to some websites or redirect requests to a different server. Meanwhile, caching DNS records improves the response time of future DNS queries and reduces the load on the DNS server.

Smart DNS proxy

A smart DNS proxy is a proxy server optimized for streaming media content. It receives DNS requests from the client and redirects them to a DNS server optimized for streaming. This way, you can access media content without affecting the rest of their internet traffic.

SOCKS proxy

A SOCKS (Socket Secure) proxy is a proxy server that handles TCP/IP traffic from clients.

SOCKS proxies come in different versions, SOCKS5 being the latest one.

You can use SOCKS proxies for any internet traffic because they’re protocol independent.

SIP proxy

A SIP (Session Initiation Protocol) proxy is a proxy server that manages and controls the flow of SIP traffic between SIP devices in a VoIP (Voice over Internet Protocol) network.

SIP proxies can perform call routing, load balancing, and distributing SIP traffic across many servers to optimize network performance. They can also provide security features such as authentication, encryption, and denial-of-service (DoS) protection.

While proxy server types may differ, most proxy servers share the same benefits:

• Improved security. A proxy server provides an extra layer of protection because the internal network doesn’t access the internet directly. You can also adjust proxy settings to filter traffic based on specific rules, such as blocking certain websites or protocols. It can prevent malware and attacks like DDoS from reaching the local network.
• Better performance. A proxy server caches frequently accessed web content. It reduces the number of requests sent to the destination server and improves the response times. A proxy server can also compress data to reduce bandwidth usage and improve network performance.
• Access control. A proxy server can help enforce internet usage policies by filtering or blocking traffic. For example, your employer can use a proxy server to block access to social networks during work hours, while an ISP can prevent users from accessing certain websites altogether.
• Improved privacy. A proxy server masks your IP address, making it more difficult for third parties to track your internet activity. It gives you more privacy for browsing the internet.
• Reduced censorship. A proxy server can route your internet traffic through a server located in a different region or country. It helps you to access content that may be otherwise blocked or restricted.

Similarly to benefits, most proxy servers also have the same shortcomings:

• Data logging. While proxy servers can increase your privacy, they can also do the opposite – they can log your data, such as websites you visit. The proxy server administrators could access logged data and sell it to third parties. It’s a common practice when it comes to free proxy servers.
• Security risks. Proxy servers become vulnerable to security risks if administrators don’t set up and maintain them properly. A vulnerable proxy server can compromise the security of the network or the client devices. Open ports on the proxy server can also make it more vulnerable to attack.
• Lack of encryption. Most proxy servers don’t encrypt your traffic, exposing sensitive data to potential interception or surveillance.
• Increased latency. Since traffic is not routed directly to the destination, proxy servers add additional latency to the network. It can slow down network performance and internet speed.
• Limited capabilities. Some proxy servers only work with specific protocols or traffic, making them useless for different applications.
• Single point of failure. If a proxy server fails and goes offline, clients can lose access to the internet or specific services.
• Technical know-how. Implementing and maintaining a proxy server requires technical expertise, which can be a challenge for individuals and small businesses.
• Cost. Setting up and maintaining a proxy server requires additional hardware, software, and human resources, increasing costs. It can be a significant disadvantage, especially for businesses that need many servers or advanced features.
• Potential misuse by bad actors. Proxy servers hide a user’s real IP address, offering anonymity that, while enhancing privacy and security, also opens doors to misuse. Sneaker bots, for example, can use proxies to circumvent purchase limits and geographic restrictions on online stores.