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FortiGate lab 6 of 25

Source NAT: IP pools and central SNAT

Move from 'everyone hides behind the WAN address' to planned source NAT: an overload pool for staff, a one-to-one address for a partner-facing PC, a fixed-port-range pool you can trace without logs, and finally the same design in the central SNAT table.

Run this lab

It needs Lite: its 4 nodes are set to 4 vCPU and 5,632 MB in total. That fits the free demo too.

In your workspace: Shared, then FortiGate NSE 4 guided labs, then 06 - Source NAT - IP pools and central SNAT

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
Intermediate
Time
About 60 minutes
Nodes need
4 vCPU, 5,632 MB
Smallest plan
Lite

The scenario

Harbourside's ISP has given it extra public addresses on the same link: 203.0.113.100 to 203.0.113.130. Three requests arrive. A partner only accepts connections from one fixed address, so PC1 must always appear as 203.0.113.110. Everyone else should use a small shared pool (203.0.113.100–101) so the WAN address is kept for the firewall. And the legal team wants to trace any internet session back to an internal address without storing NAT logs. Later, the senior engineer asks you to move all of it into the central SNAT table.

DeviceInterfaceAddressConnects to
FGT1port1 (ISP-A)203.0.113.1/24INET, gateway 203.0.113.254
FGT1port2 (LAN)10.1.10.1/24PC1 10.1.10.10, H1 by DHCP
INETeth0203.0.113.254/24test sites 198.51.100.10–14 report the source address they see

What you’ll practise

  • Read source NAT in the session table
  • Use overload, one-to-one and fixed-port-range IP pools, and explain port block allocation
  • Explain why IP pool addresses need ARP replies or a route from the ISP
  • Order policies so a specific host gets its own NAT address
  • Switch to central NAT and rebuild the design in the central SNAT table

The tasks

  1. Start the lab
  2. See source NAT in the session table
  3. An overload pool for staff
  4. A one-to-one address for PC1
  5. Traceable NAT without logs
  6. Central SNAT

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 Source NAT - IP pools and central SNAT4 nodes and 1 network, 4 links. Every link is listed as text below the diagram.FGT1INETPC1H1LANport2eth0eth0port1eth0
4 nodes and 1 network, with the interface names each link uses.
Every link, as text
  • FGT1 port1 to INET eth0
  • FGT1 port2 to LAN (network)
  • PC1 eth0 to LAN (network)
  • H1 eth0 to LAN (network)
Nodes in Source NAT: IP pools and central SNAT, with the image each runs and the vCPU and RAM it’s set to
NodeDeviceImage in Add NodeSet to
FGT1Fortinet FortiGatefortinet-FGT-v7.0.17.M-build06821 vCPU, 2,048 MB
INETEVE-NG GUI server (Docker)eve-gui-server:latest1 vCPU, 1,024 MB
PC1EVE-NG GUI server (Docker)eve-gui-server:latest1 vCPU, 2,048 MB
H1Alpine 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 06 - Source NAT - IP pools and central SNAT 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.

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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.