CloudLabBox
Try the free demo

FortiGate lab 24 of 25

Troubleshooting: VPN and authentication faults

The branch tunnel is down and directory logins fail. Work through six stacked faults in phase 1, phase 2, policies, LDAP and RADIUS with the IKE debug, the tunnel lists, debug flow, fnbamd and the directory server's own log.

Run this lab

It needs Lite: its 6 nodes are set to 6 vCPU and 7,168 MB in total. That fits the free demo too.

In your workspace: Shared, then FortiGate NSE 4 guided labs, then 24 - Troubleshooting - VPN and authentication faults

Try it free for 30 minutesRun it on Lite from £3 a day

The free demo needs no card and no email. Every lab plan includes every guided lab.

Level
Advanced
Time
About 75 minutes
Nodes need
6 vCPU, 7,168 MB
Smallest plan
Lite

The scenario

A colleague rebuilt the Cardiff branch FortiGate and "tidied up" head office's VPN and directory settings on the same afternoon. Now the branch can't reach head office, and the FortiGate's LDAP and RADIUS tests fail, so nobody can use directory logins. The intended design is the one from labs 11 and 17: an IKEv2 tunnel with des-sha256, DH 14 and key LabVpnKey1!, protecting 10.1.10.0/24 ↔ 10.2.10.0/24 in both directions; LDAP base DN DC=corp,DC=lab; RADIUS secret RadSecret1!. Find and fix every fault.

DeviceInterfaceAddressConnects to
FGT-HQport1 / port2 / port3203.0.113.1 / 10.1.10.1 / 10.1.30.1 (/24)Internet / H1 10.1.10.50 / SRV1 10.1.30.10
FGT-BRport1 / port2203.0.113.2 / 10.2.10.1 (/24)Internet / H2 10.2.10.50

Evaluation licence. These FortiGates run with low-strength encryption only, so IPsec offers DES only (des-md5 to des-sha512): no AES, no 3DES. The tunnel is meant to use des-sha256 with DH group 14. Never use DES in production: use AES-256-GCM (aes256gcm-prfsha384) with DH group 19, 20 or 21.

What you’ll practise

  • Read IKE debug output to tell proposal, authentication and selector failures apart
  • Use tunnel summaries, gateway lists and debug flow to find one-way traffic
  • Debug LDAP and RADIUS from both ends: fnbamd on the FortiGate and the server log
  • Record each fault as symptom, evidence, root cause and fix

The tasks

  1. Start the lab
  2. Collect the symptoms
  3. Phase 1
  4. Phase 2
  5. Traffic works one way only
  6. LDAP
  7. RADIUS

The Lab Tasks pane has the scenario, these tasks, the checks to run, hints and the full solution.

Topology and devices

The network as it opens in EVE-NG, drawn from the lab’s own canvas, and the image each node runs.

Topology of Troubleshooting - VPN and authentication faults6 nodes and 1 network, 6 links. Every link is listed as text below the diagram.FGT-HQFGT-BRINETSRV1H1H2Interneteth0port1port1port3eth0port2eth0port2eth0
6 nodes and 1 network, with the interface names each link uses. On a narrow screen, scroll the diagram sideways.
Every link, as text
  • FGT-HQ port1 to Internet (network)
  • FGT-BR port1 to Internet (network)
  • INET eth0 to Internet (network)
  • FGT-HQ port2 to H1 eth0
  • FGT-HQ port3 to SRV1 eth0
  • FGT-BR port2 to H2 eth0
Nodes in Troubleshooting: VPN and authentication faults, with the image each runs and the vCPU and RAM it’s set to
NodeDeviceImage in Add NodeSet to
FGT-HQFortinet FortiGatefortinet-FGT-v7.0.17.M-build06821 vCPU, 2,048 MB
FGT-BRFortinet FortiGatefortinet-FGT-v7.0.17.M-build06821 vCPU, 2,048 MB
INETEVE-NG GUI server (Docker)eve-gui-server:latest1 vCPU, 1,024 MB
SRV1EVE-NG GUI server (Docker)eve-gui-server:latest1 vCPU, 1,024 MB
H1Alpine Linuxclbalpinebase-alpine-base-3-20-31 vCPU, 512 MB
H2Alpine Linuxclbalpinebase-alpine-base-3-20-31 vCPU, 512 MB

How to open this lab

  1. Sign in to your workspace at lab.cloudlabbox.com.

  2. In File Manager, open Shared, then the folder FortiGate NSE 4 guided labs.

  3. Open 24 - Troubleshooting - VPN and authentication faults and start its nodes, then open Lab Tasks for the scenario and the steps.

The lab is read-only. You can start the nodes and configure the devices, but changes to the topology can’t be saved. To change it, rebuild it in your own folder.

More FortiGate labs

All FortiGate labs

Related labs in other courses

CloudLabBox is independent of Fortinet. The lab follows exam topics and isn’t vendor training material; vendor names identify the exams and the images in the workspace.