FortiGate 500D vs 900D vs 1240B: Mid-Range Firewalls Compared

Aug 10 , 2026 4

TL;DR: The FortiGate 500D and 900D are the mid-range workhorses of the D generation — past end of sale but still among the best value firewalls on the used market — while the 1240B is older B-generation hardware with a narrow FortiOS ceiling. For mid-size sites and campus edges, a tested used 500D or 900D is a strong buy; treat the 1240B as lab-only.

The D Generation in Context

Fortinet's D generation (2015 era) replaced the C generation and introduced the modern FortiOS feature baseline: FortiLink, SD-WAN foundations, UTM and central management. The D series is now past end of sale with EOL milestones in place, which does two things: prices on the used market fall to very attractive levels, and the support window shrinks. Both facts matter differently depending on your role — see the lifecycle detail in our FortiGate D and E series EOL list.

The 500D: Mid-Size Standard

The FG-500D pairs 8x 1GbE RJ45 with 8x 1GbE SFP — the classic mid-size enterprise shape. On the used market it is one of the highest-volume FortiGates, which keeps pricing low and spare parts plentiful. Typical roles: campus edge, branch aggregation, data center gateway for smaller facilities, and UTM for 500-1,000-user sites.

The 900D: More Headroom

The FG-900D sits one tier up with roughly double the throughput of the 500D, suiting larger sites, gigabit WANs and environments running heavy inspection. It shares the D-series feature set and FortiManager integration, so moving policies between 500D and 900D units is trivial. Used supply is healthy; pricing sits modestly above the 500D.

The 1240B: Know the Ceiling

The FortiGate-1240B is a high-capacity unit from the B generation — powerful in raw throughput, but its FortiOS ceiling and support status are older than the D series. That combination limits it to lab, isolated-segment or short-bridge duty. If you need B-generation capacity for a legacy fleet, buy tested with a warranty and verify the FortiOS ceiling first; otherwise prefer the D series for any new role.

Used Buying Checks

• FortiOS ceiling: confirm the maximum supported release for the model, and that it covers the features you need (SD-WAN, FortiLink).
• Licensing: FortiGuard subscriptions are separate from hardware; budget the license tier separately.
• Testing: both WAN and switch ports, SFP slots and console — per-port evidence, as with any used unit.

If your fleet spans sizes, note that 500D, 900D and the E/F series all centralize into the same FortiManager domain — see the used FortiGate firewall stock for the full range.

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FAQ

Q: What is the difference between FortiGate 500D, 900D and 1240B?

A: They are three mid-range and high-end FortiGate platforms from the D generation and earlier B generation: the 500D suits mid-size enterprises and campus edges, the 900D adds throughput for larger sites, and the 1240B is a high-capacity unit from the B generation with older processors.

Q: Is the FortiGate D series end of life?

A: Yes, the D series (including 500D and 900D) has announced EOL milestones and is past end of sale. Used D-series units remain functional and are popular for labs and transitional roles; check the FortiGate lifecycle page for the exact dates.

Q: Can I manage 500D and 900D together?

A: Yes — both run FortiOS and can be centrally managed by FortiManager in the same policy domain as any other FortiGate.

Q: Is the 1240B too old to buy?

A: The B generation is older hardware with limited FortiOS version support. It makes sense only as very cheap capacity for lab or isolated segments — verify the maximum supported FortiOS before committing any production traffic.

Q: Which used FortiGate is best for a mid-size campus?

A: The 500D is the volume pick for mid-size sites; the 900D for aggregation or gigabit-heavy locations. Both have high used supply and low prices, and both fit standard FortiManager management.

Q: Do D-series FortiGates support FortiLink and SD-WAN?

A: Yes, D-series units support FortiLink for managed switches and APs, and FortiOS SD-WAN functions on the versions that support them. Feature depth depends on the FortiOS release the model can run.

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