Two computers on the same switch can reach each other. A third computer, connected to that same switch, cannot reach either of them. Where would you look first?
You might check the third computer’s IP settings, then its switch port and VLAN. If the computers are on different subnets, you would also check the gateway and the path between them. Following the packet and testing one explanation at a time is central to network engineering.
If you’re starting from scratch, here’s a practical path from your first lab to your first networking role.
1. Learn what happens when a device connects
Start with Ethernet, MAC addresses, IPv4 subnetting, and default gateways. Then learn what DHCP and DNS do. Connect these concepts to an action you perform every day, such as opening a website.
Build a small lab with a switch, a router, and two clients. Give the clients static addresses first, then configure DHCP. Capture traffic as a client renews its lease or resolves a hostname. Try to explain what each packet is doing before checking the answer.
Move on when you can explain how a device gets an address, resolves a name, and decides whether to send traffic directly to another host or through its gateway.
2. Build a network you can break and fix
Create two VLANs, put a client in each, and configure routing between them. Use a simulator or equipment you can safely reset. Draw the topology and write down the expected traffic path before configuring anything.
- Assign a client port to the wrong VLAN.
- Remove a VLAN from the trunk’s allowed list.
- Give one client the wrong default gateway.
- Configure an unreachable DNS server.
Introduce one fault at a time. Record the symptom, the evidence, the fix, and the verification test. Find the first point where actual behavior differs from what you expected.
3. Troubleshoot the application
Suppose a user says, “I can’t open the internal portal.” Find out whether the problem affects one user, one office, or everyone. Ask for the exact destination, the error, and when it started. Check whether anything recently changed.
Test the hostname and the application port separately. If the hostname resolves but TCP port 443 times out, follow that connection through the client route, gateway, firewall policy, and return path. If TCP connects but the browser still reports an error, investigate TLS or the application. Use the original application test to confirm recovery.
4. Add firewall and network security skills
Put a firewall between two lab networks. Allow one client to reach one internal server over HTTPS. Verify that the permitted connection works and that an unapproved connection is blocked. Find both results in the logs and explain which rule handled each one.
Next, learn source NAT, segmentation, and VPNs. Connect a remote-access VPN client and check whether it received an IP address, installed the expected route, and can reach the intended application.
For a follow-up lab, see the FortiGate Remote Access IPsec VPN with FortiClient guide.
5. Build a portfolio that shows how you think
- Switching and VLANs: demonstrate a working access port and trunk, then diagnose a missing VLAN.
- Routing and services: demonstrate communication between subnets and separate a routing failure from a DNS failure.
- Firewall policy: show one approved connection and one blocked connection, with the matching logs and verification tests.
For each lab, include a topology, a short configuration excerpt, and a one-page incident note. Use lab addresses and remove passwords or keys. In an interview, explain your first hypothesis, what you observed, and how that evidence changed your next step.
6. Prepare for your first networking role
Look at junior network support, NOC, infrastructure support, and IT support roles with networking responsibilities. Turn repeated job requirements into lab exercises. If a certification such as CCNA fits your target roles, use it to structure your study and pair each topic with a practical test.
A useful readiness check is whether you can investigate a report such as “the VPN connects, but the portal doesn’t open” without changing several things at once. Identify the affected flow, collect evidence, explain the next step, and verify the result.
Learn with Cisco Networking Academy and FDM Akademi
If you prefer a structured learning path, explore the free online courses offered through Cisco Networking Academy. Start with networking fundamentals and practice what you learn in your own lab.
Interested in learning with us? If there’s enough interest, we can open an online networking class through FDM Akademi. Follow Firewall Support Center for course announcements and let us know which topics you’d like us to cover.
Start this week: Build a two-VLAN lab. Remove one VLAN from the trunk, trace the failure, restore it, and write down the observation that proved where the problem was. That exercise gives you your first portfolio entry.