Extending Your Network

This room builds on what we’ve learned so far and zooms out a bit. Now that we understand how data travels, we look at the technologies that make networks bigger, more secure, and more connected. Things like port forwarding, firewalls, VPNs, routers and switches.

Tasks

Task 1 — Introduction to Port Forwarding

Without port forwarding, services running on a device are only reachable from within the same local network. That’s called an intranet. A private network that no one from the outside can access.

Say you have a web server running on 192.168.1.10 at port 80. The other computers on your local network can reach it just fine. But anyone on the Internet? No chance. They have no idea it exists.

Port forwarding fixes that. You configure the router to forward incoming traffic on a specific port to the right device on the internal network. So if someone from the outside sends a request to your public IP on port 80, the router knows to pass it along to 192.168.1.10.

One thing worth clarifying early: port forwarding is not the same as a firewall. Port forwarding opens a specific port so traffic can come through. A firewall decides whether that traffic is actually allowed. They work together, but they’re different things.

Port forwarding is always configured at the router.

Question: What is the name of the device that is used to configure port forwarding? Router

Task 2 — Firewalls 101

A firewall is essentially the gatekeeper of a network. It sits at the edge and decides what traffic is allowed in and out, based on rules set by an administrator.

Those rules can be based on a lot of things:

Firewalls inspect packets to answer these questions. There are two main types:

Firewalls operate at Layers 3 and 4 of the OSI model. The Network and Transport layers. That’s where IP addresses and ports live.

Question: What layers of the OSI model do firewalls operate at? 3 & 4

Question: What category of firewall inspects the entire connection? Stateful

Question: What category of firewall inspects individual packets? Stateless

Task 3 — Practical — Firewall

Interactive task where you configure a firewall to block malicious traffic. The red packets are the bad ones, green are legitimate. The goal is to block port 80 traffic from reaching the web server at 203.0.110.1 while keeping the good traffic flowing through.

Question: What is the flag? THM{FIREWALLS_RULE}

Task 4 — VPN Basics

A VPN (Virtual Private Network) lets devices on completely separate networks communicate securely over the Internet, as if they were on the same local network. It does this by creating an encrypted tunnel between the devices.

A good real world example: a company with two offices in different cities. Instead of paying for a dedicated private line between them, they use a VPN. Both offices can share resources like servers and printers as if they were in the same building.

VPNs offer three main benefits:

There are a few different VPN technologies in use:

TryHackMe actually uses a VPN to connect you to their vulnerable machines. Keeping them off the public Internet while still letting you reach them.

Question: What VPN technology only encrypts & provides the authentication of data? PPP

Question: What VPN technology uses the IP framework? IPSec

Task 5 — LAN Networking Devices

This task covers two core pieces of networking hardware: routers and switches. They often get confused but do very different things.

Routers connect separate networks and pass data between them. That process is called routing. Routers operate at Layer 3 of the OSI model and use IP addresses to figure out the best path for data to travel. They often have a web interface or console where an administrator can configure things like port forwarding or firewall rules.

When there are multiple paths between two devices, the router picks the best one based on factors like:

Switches are different. Their job is to connect multiple devices within the same network. Think of the central hub that all the computers in an office plug into. They can work at two different layers:

One more concept introduced here: VLAN (Virtual Local Area Network). VLANs let you logically split up devices on the same physical switch into separate groups. For example, the Sales team and the Accounting team might be on the same switch, but a VLAN keeps them isolated from each other. They can both access the Internet, but they can’t talk directly to each other. Clean network separation without needing extra hardware.

Question: What is the verb for the action that a router does? Routing

Question: What are the two different layers of switches? Layer 2, Layer 3

Task 6 — Practical — Network Simulator

Fun interactive task. You get a network simulator that breaks down every single step a packet takes as it travels from one device to another. Including the full TCP handshake process.

The task is to send a TCP packet from computer1 to computer3 and watch it all unfold in the network log.

Question: What is the flag from the network simulator? THM{YOU'VE_GOT_DATA}

Question: How many HANDSHAKE entries are there in the Network Log? 5

That wraps up the Extending Your Network room. Port forwarding, firewalls, VPNs, routers, switches. These are the building blocks of every real world network out there. Once these concepts click, a lot of the more advanced security topics start to make a lot more sense.