100G QSFP28 is not a transitional speed. In 2026, it remains the workhorse standard for spine-leaf fabrics, ISP aggregation layers, and enterprise core links. Yes, 400G QSFP-DD is gaining ground in hyperscale builds — but most mid-market data centers and ISPs are still deploying 100G as their primary upgrade target from 10G and 40G infrastructure.
The optical networking hardware market hit $23 billion in 2025, up 50% year-over-year. A significant share of that volume is 100G QSFP28, driven by AI/ML cluster interconnects, 5G fronthaul and backhaul, and data center modernization projects that need cost-effective density at scale.
Choosing the wrong QSFP28 variant costs you twice: once on the wrong module, and again on the fix. This guide covers SR4, LR4, ER4, and PSM4 so you can match the right optic to your fiber plant, reach requirement, and budget on the first order.
QSFP28 carries 100G by aggregating four 25G electrical lanes. It fits the same cage footprint as QSFP+, making it a direct upgrade path for switches already populated with 40G ports — no cage swap required.
Depending on the variant, it supports both single-mode and multimode fiber. It also supports breakout configurations: one 100G QSFP28 port can split into four 25G SFP28 connections via a breakout DAC or AOC, which is useful for ToR-to-server links in high-density racks.
Reach: up to 100M on OM4 multimode fiber (70M on OM3)
SR4 runs four parallel 25G lanes over an MPO-12 connector on multimode fiber. It is the standard choice for intra-data-center links — ToR to spine, server to ToR, row-to-row — wherever fiber runs stay under 100M.
Power draw is low, typically around 3.5W, and per-module cost is the lowest of the four variants. That matters when you are populating 48-port spine switches. SR4 does not work on single-mode fiber, and it requires MPO/MTP trunk cabling rather than LC duplex.
Use SR4 when your fiber plant is multimode and your runs stay inside a single building or campus.
Reach: up to 10KM on single-mode fiber (LC duplex)
LR4 uses WDM to multiplex four 25G lanes onto four separate wavelengths — 1295nm, 1300nm, 1305nm, 1310nm — over a single LC duplex SMF connection. That means it works with standard single-mode patch panels without any MPO infrastructure.
It is the default choice for inter-building campus links, metro DCI under 10KM, and ISP aggregation where single-mode fiber is already in place. Power draw is higher than SR4, typically 4 to 5W, and module cost reflects that. If you are upgrading an existing 10G single-mode plant to 100G without rerunning fiber, LR4 drops in without infrastructure changes.
Reach: up to 40KM on single-mode fiber (LC duplex)
ER4 extends the LR4 architecture to 40KM using higher-output lasers and either an integrated semiconductor optical amplifier (SOA) or APD receiver, depending on the implementation. It uses the same four-wavelength LAN-WDM scheme and LC duplex connector as LR4.
This is the right module for metro DCI, ISP edge-to-core links, and enterprise WAN connections where 10KM falls short but full DWDM infrastructure is not justified. Power consumption rises to 7 to 9W, and these are among the more expensive 100G QSFP28 variants. Do not spec ER4 where LR4 covers your reach — the cost and power premium is not worth it for links under 10KM.
Reach: up to 500M on single-mode fiber (MPO-12)
PSM4 sends four parallel 25G lanes over four single-mode fiber pairs via an MPO-12 connector. There is no WDM multiplexing, which keeps the optics simpler and the cost lower than LR4 — while still running on single-mode fiber.
PSM4 targets hyperscale data center interconnects in the 100M to 500M range where multimode fiber is not available but full LR4 reach is not needed. It requires MPO infrastructure on single-mode fiber, which is less common in legacy enterprise plants but increasingly standard in new hyperscale builds. Outside of that context, PSM4 sees limited deployment in ISP or enterprise networks.
| Variant | Max Reach | Fiber Type | Connector | Lanes | Typical Use Case |
|---|---|---|---|---|---|
| SR4 | 100M (OM4) | Multimode | MPO-12 | 4x25G parallel | Intra-DC, ToR to spine |
| LR4 | 10KM | Single-mode | LC duplex | 4x25G WDM | Campus DCI, metro ISP |
| ER4 | 40KM | Single-mode | LC duplex | 4x25G WDM | Metro DCI, ISP edge-core |
| PSM4 | 500M | Single-mode | MPO-12 | 4x25G parallel | Hyperscale intra-campus |
Intra-data-center, runs under 100M, multimode plant: SR4. Lowest cost, lowest power, and purpose-built for this scenario. Pair it with OM4 MPO trunk cables and you are done.
Campus or metro DCI, existing single-mode LC infrastructure, runs under 10KM: LR4. No MPO required, drops into your existing patch panels, and covers the vast majority of enterprise and ISP aggregation distances.
Metro ISP links or DCI between 10KM and 40KM: ER4. The only 100G QSFP28 variant that covers this range without moving to DWDM line cards. Budget for the higher power draw.
Hyperscale or colo builds with single-mode MPO infrastructure, runs between 100M and 500M: PSM4. Lower cost than LR4 at these distances, but only practical if you already have — or are actively building — single-mode MPO infrastructure.
Breakout to 25G servers: SR4 or PSM4 with an MPO breakout cable. LR4 does not support native breakout because all four wavelengths land on a single LC port.
Third-party 100G QSFP28 modules work with Cisco, Juniper, Huawei, Arista, Dell, and other major switch platforms when properly programmed. The critical variable is EEPROM programming — the module must identify itself correctly to the host switch, or you will hit "unsupported transceiver" errors before the link ever comes up.
Before committing to a bulk order, validate against your specific switch model and firmware version. Compatibility test videos are a practical shortcut. Hytoptodevice publishes compatibility test videos showing modules operating in named switch platforms, and product datasheets are available for download to support your pre-purchase review.
In mixed-vendor environments, note that Cisco IOS-XE and NX-OS handle third-party module detection differently. Some platforms require a service unsupported-transceiver command to enable non-OEM modules. Junos handles this more transparently. Check your platform documentation before deployment.
A Cisco-branded 100G QSFP28 LR4 typically runs $200 to $500 or more per unit through standard channels. At 48 ports per switch, that is $9,600 to $24,000 in optics for a single line card — before spares.
Verified third-party compatible modules deliver 70 to 90% cost savings over OEM pricing. At scale, that difference funds additional switch capacity, a meaningful spares inventory, or simply comes back to the project budget.
The compatibility risk that historically justified OEM premiums has narrowed considerably. Third-party modules with published test data and proper EEPROM programming perform to the same IEEE and MSA specifications as OEM equivalents. The question is not whether they work — it is whether you have validated the specific module against your specific platform. That is what datasheets and compatibility test videos are for.
Hytoptodevice stocks the full 100G QSFP28 collection — SR4, LR4, and additional variants — at hytoptodevice.com/collections/100g-qsfp28. The catalog spans 1.25G to 800G across eight form factors, so if your project also calls for 25G SFP28, 400G QSFP-DD, or AOC and DAC cables for short-range interconnects, you source everything from a single account.
For teams running OEM or white-label programs, the OEM/ODM solutions page covers custom-programmed and white-label module options for runs in the 100 to 1,000 unit range — a scale most direct competitors do not support.
Product downloads and compatibility test videos are available before you commit to a purchase, so your technical validation can happen before the order goes in. Sign up at hytoptodevice.com to access account pricing and submit a quote request.
Q1: Can I use a 100G QSFP28 SR4 module in a QSFP+ port?
A: No. QSFP28 and QSFP+ share the same physical cage dimensions, but the electrical interface is different. QSFP28 uses 4x25G lanes; QSFP+ uses 4x10G lanes. A QSFP28 module will not function in a QSFP+ port, and vice versa.
Q2: What fiber type does 100G QSFP28 LR4 require?
A: LR4 requires OS2 single-mode fiber with LC duplex connectors. It does not work on multimode fiber. If your existing plant is OM3 or OM4, you need SR4, not LR4.
Q3: Does 100G QSFP28 support breakout to 4x25G?
A: SR4 and PSM4 both support breakout to 4x25G SFP28 using an MPO-to-4xLC breakout cable, since both use four parallel fiber lanes. LR4 does not support breakout — all four wavelengths are multiplexed onto a single LC port.
Q4: How do I avoid "unsupported transceiver" errors with third-party 100G QSFP28 modules on Cisco switches?
A: On Cisco IOS-XE and NX-OS platforms, enter service unsupported-transceiver in global configuration mode to enable non-OEM modules. Some platforms also require a specific license. Check your platform release notes and confirm the module's EEPROM is programmed to match your switch's expected vendor ID.
Q5: What is the power consumption difference between SR4 and ER4?
A: SR4 draws around 3.5W. ER4 draws 7 to 9W due to the higher-output lasers and amplification required for 40KM reach. In a high-density chassis, that gap becomes meaningful fast when you are calculating power and thermal budgets at scale.
Q6: Is PSM4 interchangeable with LR4?
A: No. PSM4 uses an MPO-12 connector over four parallel single-mode fiber pairs. LR4 uses an LC duplex connector with WDM multiplexing. They are not physically or optically interchangeable. Confirm your fiber infrastructure before specifying either variant.
Q7: What is the maximum reach of 100G QSFP28 ER4?
A: ER4 is rated for up to 40KM on OS2 single-mode fiber. Beyond 40KM at 100G, you move to DWDM-based solutions with external amplification — a different product category entirely.
SR4 for short-reach multimode. LR4 for standard single-mode campus and metro links. ER4 for 40KM metro DCI. PSM4 for hyperscale single-mode MPO builds. Match the variant to your fiber plant and reach requirement before anything else.
Start with the compatibility test videos and datasheets to validate against your switch platform, then place your order with confidence. Browse the full 100G QSFP28 collection at hytoptodevice.com.
