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OOTW / Chapter I - Foundation / 03. Networking / 07. Proxy

Proxy

So far we have discussed:

  • Network Segmentation
  • Routing
  • Netmasks
  • VPNs

We now understand how systems communicate.

The next question is:

Can a third system sit between
the client and the destination?

The answer is - yes. This intermediary system is called a "Proxy".

What Is A Proxy?

A proxy is a system that receives traffic on behalf of another system.

Instead of:

Client
│
▼
Server

we have:

Client
│
▼
Proxy
│
▼
Server

The proxy becomes the middleman.

Why Proxies Exist

Proxies are used for:

  • Security
  • Logging
  • Filtering
  • Caching
  • Access Control
  • Traffic Inspection
  • Load Balancing

Many enterprise networks use proxies extensively.

The Two Main Types

There are two major proxy categories:

Forward Proxy

and

Reverse Proxy

Understanding the difference is critical.

Forward Proxy

A forward proxy represents:

The Client

Visualized:

Client
   │
   ▼
Forward Proxy
   │
   ▼
Internet

The destination server sees:

The Proxy

not necessarily the client.

Forward Proxy Example

Many organizations force employees through a proxy.

Employee
    │
    ▼
Corporate Proxy
    │
    ▼
Internet

Benefits:

Logging
Filtering
Monitoring
Malware Protection

Suppose:

Employee

visits:

google.com

The flow becomes:

Employee
│
▼
Proxy
│
▼
Google

Google sees:

Proxy IP

instead of:

Employee IP

Reverse Proxy

A reverse proxy represents:

The Server

Visualized:

Client
    │
    ▼
Reverse Proxy
    │
    ▼
Web Server

The client may never directly communicate with the backend server.

Benefits include:

Security
TLS Termination
Load Balancing
Caching
DDoS Protection

Many websites on the Internet use reverse proxies.

Reverse Proxy Example

Instead of:

Internet
     │
     ▼
Web Server

you may have:

Internet
     │
     ▼
NGINX
     │
     ▼
Backend Web Server

The NGINX server acts as a reverse proxy.

Many organizations expose:

https://company.com

but internally:

App Server 1
App Server 2
App Server 3

Visualized:

Internet
     │
     ▼
Reverse Proxy
     │
 ┌───┼───┐
 │   │   │
 ▼   ▼   ▼

App1 App2 App3

The reverse proxy distributes traffic.

Load Balancing

One common reverse proxy feature is:

Load Balancing

Instead of:

1000 Users
    │
    ▼
One Server

we get:

1000 Users
        │
        ▼
Reverse Proxy

     ┌──┼──┐

     ▼  ▼  ▼

   App1 App2 App3

Traffic is distributed.

TLS Termination

Many reverse proxies handle TLS.

Example:

Internet
    │
 HTTPS (encrypted)
    │
    ▼
Reverse Proxy (TLS termination)
    │
 HTTP (unencrypted)
    │
    ▼
Backend

The backend never directly handles TLS.

Common Forward Proxies

Examples:

Squid
Blue Coat
Zscaler

Common Reverse Proxies

Examples:

NGINX
HAProxy
Traefik
Apache
Envoy

Note: do not try to memorize every single tool name you encounter, just try to understand the principles.

Proxy Chains

Sometimes multiple proxies exist.

Example:

Client
    │
    ▼
Forward Proxy
    │
    ▼
Internet
    │
    ▼
Reverse Proxy
    │
    ▼
Backend Server

A single request may traverse several proxies before reaching its destination.

Proxies And Security

From an operator's perspective, proxies often become important infrastructure components.

Reasons include:

Traffic Inspection
Authentication
Filtering
Logging

and

Application Exposure

Many externally accessible services are actually reverse proxies sitting in front of internal applications.

Real World Example

Consider:

company.com

An attacker may believe they are targeting:

Web Server

when in reality:

Internet
      │
      ▼
Cloudflare
      │
      ▼
NGINX
      │
      ▼
Application

Several proxy layers may exist.

Operator Notes

The easiest way to remember proxies is:

Forward Proxy
=
Represents The Client

Reverse Proxy
=
Represents The Server

Visualized:

Forward Proxy

Client
   ▼
Proxy
   ▼
Internet

Reverse Proxy

Internet
   ▼
Proxy
   ▼
Server

This distinction appears everywhere:

  • Corporate Networks
  • Cloud Infrastructure
  • Kubernetes
  • Red Team Infrastructure
  • CDNs
  • Web Applications

Understanding proxies is essential because modern environments rarely expose systems directly. Most traffic passes through one or more intermediary systems before reaching its final destination.