1. Switch and NIC platforms
The Asteraix CX732Q-N is a 1U, 32-port 400G QSFP-DD switch built on the Marvell Teralynx 7 ASIC. Switching capacity is 12.8 Tbps, packet buffer is 70 MB, forwarding rate is 7,600 Mpps, and cut-through latency is sub-500 ns. AsterNOS (enterprise SONiC) is preinstalled with RoCEv2, PFC, ECN, DCBX, BGP-EVPN, VXLAN, and MLAG. Typical roles are spine and super-spine in AI/HPC fabrics, and increasingly the accept-layer switch for 400G storage nodes.
On the storage side, the two NICs in production today are NVIDIA ConnectX-7 and BlueField-3.
ConnectX-7 ships in three port configurations:
Single-port 400Gb/s, OSFP cage, RHS (riding heatsink) shell only.
Dual-port 200Gb/s each, QSFP112 cage — this is the highest-volume ConnectX-7 SKU.
Dual-port 100Gb/s or lower, QSFP56/SFP56 — outside the scope of this article.
BlueField-3 uses QSFP112 cages exclusively; it never ships with an OSFP cage. Depending on model, it appears as a single 400GbE/NDR port (e.g. B3140H) or two QSFP112 ports running 200GbE/NDR200 each, with some dual-port models supporting 400GbE per port (B3240). For this article, "BlueField-3 port" means a QSFP112 cage running at up to 400G per port.
Both ConnectX-7 and BlueField-3 use RHS (riding heatsink) cage shells only — this matters when picking modules, covered in Section 6.
2. Why a passive 400G DAC will not connect switch to NIC
CX732Q-N's QSFP-DD cage electrical interface is 8 lanes at 50G PAM4. ConnectX-7 and BlueField-3's OSFP/QSFP112 electrical interface is 4 lanes at 100G PAM4. A passive copper cable carries signal without retiming or lane remapping, so both ends need matching lane count and per-lane rate. 8×50G and 4×100G don't match, so a straight passive DAC between the switch and either NIC is not an option, regardless of reach.
Two connection methods remain:
Module pair over fiber — one optical module in the switch, one optical module (or NIC-side module) in the NIC, connected by patch fiber. Each module's internal DSP handles the lane remap on its own side.
Active cable (AOC/AEC) — a single cable with a transceiver-equivalent engine at each end, already remapped for the connector type on either side. No separate modules, no patch fiber.
3. CX732Q-N side modules (in stock)
Part | Spec |
|---|---|
OT-400G-QDD-DR4 | 400G QSFP56-DD DR4, MPO-12/APC, 1310nm, single-mode, 500m |
OT-400G-QDD-SR4 | 400G QSFP56-DD SR4, MPO-12/APC, 850nm, OM4, 100m |
OT-400G-QDD-FR4 | 400G QSFP56-DD FR4, duplex LC, 1310nm, single-mode, 2km |
These three are the switch-side half of every module-pair link described below.
4. ConnectX-7 single-port OSFP (400G)
NIC side needs an OSFP112, RHS-shell module, matched to the switch-side QSFP-DD module by reach and wavelength.
Module pair:
Reach | Switch side | NIC side |
|---|---|---|
500m, single-mode | OT-400G-QDD-DR4 | OT-400G-OSFP112R-DR4 |
100m, OM4 | OT-400G-QDD-SR4 | OT-400G-OSFP112R-SR4 |
Active cable, one cable end to end:
AOC-400G-QDD-OSFP112R, QSFP-DD end into the switch, OSFP112-RHS end into the NIC, 1–50m. No separate modules or patch fiber required.
5. ConnectX-7 dual-port QSFP112 (2×200G, highest-volume SKU)
Each of the two ports carries 200G independently. Do not treat the pair as a single 400G link, and do not plug a 400G module into either port.
Switch 400G port broken out to the NIC's two 200G ports:
AOC-400G-QDD-2*QSFP: one QSFP-DD end into the switch, breaking out to two QSFP56 ends, one into each NIC port, 1–100m.
NIC to a device with native 200G QSFP56 ports (module pair):
Reach | Both ends |
|---|---|
100m, OM4 | OT-200G-QSFP-SR4 |
2km, single-mode | OT-200G-QSFP-FR4 |
Short-reach copper:
DAC-200G-QSFP, 200G QSFP56 to 200G QSFP56, 1–3m. Only for direct connections where both ends are native 200G QSFP56 ports — this cable cannot connect to CX732Q-N's 400G QSFP-DD port (see Section 2).
6. BlueField-3 QSFP112 port (up to 400G)
NIC side needs a QSFP112 module (non-RHS shell) — do not confuse this with the OSFP112-RHS parts used for ConnectX-7's single-port OSFP variant in Section 4; the cage and shell are different even though both are "112" family optics.
Module pair:
Reach | Switch side | NIC side |
|---|---|---|
100m, OM4 | OT-400G-QDD-SR4 | OT-400G-QSFP-SR4 |
2km, single-mode | OT-400G-QDD-FR4 | OT-400G-QSFP-FR4 |
Short reach, lower cost:
OT-400G-QSFP-VR4, 50m, OM4. VR4 uses a different optical engine than SR4 and cannot mix with SR4 modules on the same link. Confirm switch-side VR4 stock before ordering.
Active cable, one cable end to end:
AOC-400G-QSFP-QDD, QSFP-DD end into the switch, QSFP112 end into the NIC, 1–50m.
7. Legacy 100G storage controllers
Some storage arrays still run 100G QSFP28 host ports. DAC-100G-QSFP (100G QSFP28 to 100G QSFP28, 1–5m) connects two such ports directly. It requires native 100G QSFP28 on both ends and cannot connect to CX732Q-N's 400G QSFP-DD port. Arrays in this category typically attach through a separate 100G leaf switch rather than directly to CX732Q-N.
8. Selection reference table
NIC port | Scenario | Switch side | NIC side |
|---|---|---|---|
Single-port OSFP | 500m, single-mode | ||
Single-port OSFP | 100m, OM4 | ||
Single-port OSFP | One cable, ≤50m | same | |
Dual-port 2×200G | Breakout to switch, ≤100m | same | |
Dual-port 2×200G | Native 200G peer, 100m OM4 | OT-200G-QSFP-SR4 | |
Dual-port 2×200G | Native 200G peer, 2km single-mode | OT-200G-QSFP-FR4 | |
Dual-port 2×200G | ≤3m copper | same | |
QSFP112 (BlueField-3) | 100m, OM4 | ||
QSFP112 (BlueField-3) | 2km, single-mode | ||
QSFP112 (BlueField-3) | 50m, OM4, lower cost | confirm switch-side VR4 stock | |
QSFP112 (BlueField-3) | One cable, ≤50m | same |
What not to do
Do not connect switch and NIC with a passive 400G DAC. The electrical lane structure doesn't match on the two ends (Section 2).
Do not plug a 400G QSFP112 module into a ConnectX-7 dual-port 2×200G cage, or the reverse. Each 200G port is an independent link.
SR8 (MPO-16), ZR4, and LR4 are out of scope — neither ConnectX-7 nor BlueField-3 has a matching NIC-side module for these.
Do not mix VR4 and SR4 modules on the same link. Both use MPO-12/APC and OM4, but the optical engines are different and won't interoperate.
Do not order a finned OSFP module for the NIC side. ConnectX-7's OSFP cage takes RHS (riding heatsink) shells only; finned modules are built for switch panels, not NIC brackets.
