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Advanced Topic 39 of 50 Computer Networks

Proxies

Intermediaries forwarding requests on behalf of clients or servers.

How it works

A proxy is an intermediary that handles requests on behalf of others. A forward proxy sits in front of clients, controlling, filtering or caching outbound traffic and hiding client identity, while a reverse proxy sits in front of servers, handling TLS, caching, compression, routing and protection for the backends. Transparent proxies intercept traffic without client configuration, and SOCKS and HTTP CONNECT tunnel arbitrary traffic.

Step-by-step walkthrough

  1. A forward proxy sits in front of clients and requests on their behalf.
  2. It can filter, cache and hide client addresses.
  3. A reverse proxy sits in front of servers.
  4. It handles TLS, caching and load balancing.
  5. Clients talk to it without knowing the real servers.

Where it is used

Corporate content filtering, caching of downloads, API gateways, web application firewalls, CDNs and service meshes use proxies such as Squid, NGINX, Envoy and HAProxy.

Common pitfall

Proxies add latency and a point of failure, and can see unencrypted traffic, which raises privacy concerns. TLS interception breaks end-to-end security assumptions. Misconfigured open proxies are abused by attackers. Preserve client IPs through headers such as X-Forwarded-For and validate them carefully, because clients can forge them.

Where it fits in the course

Proxies is topic 39 of 50 in Computer Networks, rated Advanced. It follows Load Balancers. The next topic is Firewalls.

Practice and explore

How to study this topic

  1. Read the explanation above and restate the definition in your own words.
  2. Open the interactive lesson and answer its mini quiz.
  3. Read the common pitfall, then write a short example that avoids it.
  4. Check your understanding in the Computer Networks quiz, and revisit the topic if you miss a question.

Frequently asked questions

What is Proxies?
Intermediaries forwarding requests on behalf of clients or servers. It belongs to Computer Networks and is an advanced-level topic.
Where do people use Proxies?
Corporate content filtering, caching of downloads, API gateways, web application firewalls, CDNs and service meshes use proxies such as Squid, NGINX, Envoy and HAProxy.
What is the most common mistake with Proxies?
Proxies add latency and a point of failure, and can see unencrypted traffic, which raises privacy concerns.
What should I learn before this topic?
Start with Load Balancers, the topic just before it in Computer Networks.
How can I practice it?
Answer the mini quiz in the interactive lesson, then take the Computer Networks quiz.
Is Proxies hard to learn?
It is an Advanced topic. Expect to read the explanation more than once and to connect it with earlier topics. Working through a small example by hand helps most.
How long does it take to learn Proxies?
Most learners can read the explanation and finish the interactive lesson in under an hour. Fluency comes from applying the idea, so plan a few short practice sessions with the quiz.
Which topics are related to Proxies?
Load Balancers, Firewalls, CDN are closely connected. The full list is in the related topics section of this page.
What should I study after Proxies?
Continue with Firewalls, the next topic in Computer Networks.

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