Yes, a DGX Spark can join a 100G network, but the cable matters more than usual. Its ConnectX-7 QSFP ports run Ethernet at up to 200 Gb/s and will link at 100 Gb/s to a QSFP28 switch port. A 100G QSFP28 passive DAC is the dependable way to do it: owners report 100G coming up over DAC where 100G SR4 optics would not. The other workarounds people try fail more often. Breakout cables only light one lane on the Spark end, QSFP-to-SFP adapters are untested, and a direct link to a Jetson AGX Thor hasn't been shown to stay up. For a NAS, the Spark's built-in 10GbE port is often all you need.
Below: what to use for each connection, why the common workarounds fail, and the switch settings that bring a 100G link up.
Short answer: a 100G QSFP28 DAC, coded for your switch
Link a DGX Spark to a 100G switch with a QSFP28 DAC — from $38 at Resilient Tec
Plug a 100G QSFP28 passive DAC from a Spark QSFP port into a 100G switch port, fix the switch port at 100G and match FEC. Order the cable coded for your switch brand; switches check coding more strictly than the Spark's ConnectX-7 does.
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MCP1600-C001 — 100G QSFP28 DAC, 1 m, NVIDIA/Mellanox-coded For NVIDIA, MikroTik and most white-box switches. |
$45 · In stock at Resilient Tec Add to cart |
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QSFP-100G-CU1M — 100G QSFP28 DAC, 1 m, Cisco-coded For Cisco Nexus and Catalyst 100G ports. |
$38.95 · In stock at Resilient Tec Add to cart |
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CAB-Q-Q-100G-1M — 100G QSFP28 DAC, 1 m, Arista-coded For Arista 100G ports. |
$38 · In stock at Resilient Tec Add to cart |
Resilient Tec sells the MCP1600-C001 for $45, the Cisco-coded DAC for $38.95 and the Arista-coded DAC for $38 directly at resilient-tec.com — new, lifetime warranty, shipping from Knoxville, Tennessee. Prices checked October 19, 2026. POs and net terms available.
What Works, Connection by Connection
| You want to connect the Spark to… | Use | Speed | Verdict |
|---|---|---|---|
| Another GB10 system | QSFP112 stacking cable or 200G QSFP56 DAC | 200 Gb/s | Documented by NVIDIA |
| A 400G switch | 200G QSFP56 DAC, or a QSFP-DD breakout on the switch end | 200 Gb/s | Documented by NVIDIA |
| A 100G switch | 100G QSFP28 passive DAC | 100 Gb/s | Works; reported in the field |
| A 100G switch over fiber | 100G QSFP28 SR4 optics + MPO fiber | 100 Gb/s | Reported failures; NVIDIA/Mellanox-coded optics suggested |
| A NAS on your existing network | The Spark's 10GbE RJ45 port | 10 Gb/s | Simplest; no QSFP needed |
| A NAS or PC with a 100G/200G QSFP card | QSFP28 DAC, or QSFP56 DAC for 200G | 100–200 Gb/s | Works for Ethernet traffic; the far end needs a QSFP NIC |
| A 25G or 10G SFP switch | Spark-side breakout or QSA adapter | 25 Gb/s at best | Not recommended; use the 10GbE port or a 100G uplink |
| A Jetson AGX Thor | Through a switch | Up to 25–100 Gb/s | Direct link not proven; go through a switch |
100G Switches: Use a DAC, Coded for the Switch
The Spark's ConnectX-7 is a 200GbE adapter that also runs at 100GbE. A standard QSFP28 plug fits its QSFP112 cage, and the link comes up at 100 Gb/s. On NVIDIA's developer forum, an owner whose 100G optics refused to link reported that a 100G DAC worked on the same setup. For a Spark sitting near its switch, a passive DAC is also the cheapest and coolest option.
Coding matters at the switch end. Cisco, Arista, Dell and Juniper switches read the cable's EEPROM and can reject a cable coded for another vendor. NVIDIA ConnectX adapters are generally more tolerant. So pick the DAC by the switch you're plugging into:
| Switch | Cable to order | Price at Resilient Tec |
|---|---|---|
| NVIDIA / Mellanox, MikroTik, most white-box | MCP1600-C001 (1 m) or MCP1600-C003 (3 m) | $45 / $92 |
| Cisco | QSFP-100G-CU1M compatible (1 m) | $38.95 |
| Arista | CAB-Q-Q-100G-1M compatible (1 m) | $38 |
| Dell | DAC-Q28-100G-1M compatible (1 m) | $38 |
Not on the list? We code DACs for most switch brands; send us the switch model.
Bringing the link up:
- Fix the switch port at 100G rather than relying on auto-negotiation between a 200G NIC and a 100G port.
- Match FEC on both ends. 100G over copper normally uses RS-FEC, and a mismatch shows as "cable detected, no link". See DAC cable no link? Fix FEC mismatches.
- Check the link from the Spark with
ethtoolon the interface, ormlxlinkfor the full picture. See the mlxlink and mst field guide. - Remember that each Spark port appears as two Linux interfaces. For ordinary switch traffic you only need to address one of them.
Why 100G Optics Are the Risky Route
The most-viewed 100G thread on NVIDIA's forum is a Spark that would not link at 100G through QSFP28 SR4 optics to a UniFi aggregation switch. The owner tried every 100G speed setting and several modules. 40G optics worked, and so did a 100G DAC. The thread has no confirmed fix. The suggestions were to try NVIDIA/Mellanox-coded SR4 modules and to inspect the link with mlxlink.
Our advice: if the switch is within a few meters, use a DAC and skip the question. If you need fiber, use an NVIDIA/Mellanox-coded SR4 module on the Spark end, such as the MMA1B00-C100D compatible SR4 ($94), and an SR4 coded for your switch on the other end. Then confirm the link before you build anything on it. If it won't come up, tell us the switch model and we'll help work through the coding.
Breakout Cables and QSA Adapters: Why They Disappoint
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Breakouts on the Spark end. The DGX Spark does not split its QSFP ports into lanes. Linux's
devlinkreports its ports as not splittable, and owners who put a QSFP28-to-4×SFP28 breakout on the Spark found only the first lane links. You get one 25G connection and three dead legs. Breakouts belong on the switch end, feeding Sparks from a faster port. That's covered in Can You Build a 4-Node DGX Spark Cluster Without a Switch? - QSFP-to-SFP (QSA) adapters. They let a QSFP port take a 25G or 10G SFP module. NVIDIA has not tested them on the Spark, and forum answers say so. Even when one works, you have dropped a 200G port to 25G or 10G. The Spark's built-in 10GbE port does that job without an adapter.
NAS and PCs
Most people asking how to connect a Spark to a NAS want to pull models and datasets faster. Three options, in order of effort:
- The 10GbE port. Every GB10 system has a 10GbE RJ45 port. Plug it into your existing 10G network and the NAS is reachable with no new hardware.
- A 100G switch. If the NAS already sits on a 100G switch, connect a Spark QSFP port to it with a QSFP28 DAC as above.
- Direct to the NAS or PC. The far end needs a 100G or 200G QSFP network card, such as a ConnectX-5, -6 or -7. Link the two with a QSFP28 DAC at 100G, or a 200G QSFP56 DAC ($84) if the card is 200G. Treat this as an ordinary Ethernet link; NVIDIA's clustering playbooks are written for Spark-to-Spark.
Jetson AGX Thor
Pairing a Spark (development) with a Thor (robotics) is a natural idea, but the ports don't match well. The Thor's QSFP28 port is specified as 4×25GbE, defaults to 10GbE and runs one speed at a time. The Spark's ports don't split into lanes. In the forum thread on exactly this, the owner got the interfaces to come up briefly before they dropped and stayed down, and nobody posted a working direct setup. The practical answer is a switch that supports 25GbE or 100GbE on both sides. Expect ordinary Ethernet between them: forum answers doubt that RDMA, or Thor's sensor-bridge networking, will work with a Spark.
FAQ
Can a DGX Spark connect to a 100G switch?
Yes. The Spark's ConnectX-7 QSFP ports run Ethernet at up to 200 Gb/s and will link at 100 Gb/s to a 100G QSFP28 switch port. A 100G QSFP28 passive DAC is the reliable way to do it: owners on NVIDIA's forum report 100G links coming up over DAC where 100G SR4 optics would not. Set the switch port to a fixed 100G and match FEC on both ends.
Why won't my DGX Spark link at 100G with QSFP28 SR4 optics?
It is a reported, unresolved problem. On NVIDIA's developer forum, a Spark with third-party QSFP28 SR4 optics on a UniFi aggregation switch would not link at 100G, though 40G optics and a 100G DAC both worked on the same setup. Suggestions in the thread were NVIDIA/Mellanox-coded SR4 optics and checking the link with mlxlink, but no fix was confirmed. If you can, use a DAC for runs up to a few meters.
Can I use a breakout cable to connect a DGX Spark to 25G or 10G ports?
Not usefully. The DGX Spark does not split its QSFP ports, so on the Spark end of a QSFP28-to-4×SFP28 breakout only the first lane links, giving one 25G connection at best. Breakout cables belong on the switch end, feeding Sparks from a faster switch port, never the other way round.
Can I connect a DGX Spark to a NAS?
Yes, two ways. The simplest is the Spark's built-in 10GbE RJ45 port into your existing network, which is plenty for most NAS traffic. For faster model and dataset transfers, connect a QSFP port to a 100G switch the NAS also sits on, or directly to a NAS or PC that has a 100G or 200G QSFP network card, using a QSFP28 DAC.
Can a DGX Spark connect directly to a Jetson AGX Thor?
Not reliably, as of October 2026. The Thor's QSFP28 port runs as 4×25GbE, defaults to 10GbE and runs one speed at a time, while the Spark's ports don't split into lanes. One owner on NVIDIA's forum got a direct link to come up briefly before it dropped and stayed down. The practical route is a switch that supports 25GbE or 100GbE for both. Expect ordinary Ethernet, not RDMA, between them.
Which 100G cable should I buy for a DGX Spark and a switch?
A 100G QSFP28 passive DAC coded for your switch. Resilient Tec stocks NVIDIA/Mellanox-coded MCP1600-C001 (1 m, $45) and MCP1600-C003 (3 m, $92), plus Cisco-, Arista- and Dell-coded 1 m versions from $38. All are new with a lifetime warranty. (Prices checked October 19, 2026.)
Where can I buy a 100G QSFP28 DAC for a DGX Spark?
Directly from Resilient Tec, shipping from Knoxville, Tennessee, with POs and net terms available: MCP1600-C001 1 m — $45 at resilient-tec.com, Cisco QSFP-100G-CU1M compatible — $38.95 and Arista CAB-Q-Q-100G-1M compatible — $38. All in stock at Resilient Tec. (Prices checked October 19, 2026.)
Ready to Buy?
Everything to put a DGX Spark on a 100G network. New, lifetime warranty, shipping from Knoxville, Tennessee. Prices below checked October 19, 2026.
- MCP1600-C001 compatible — 100G QSFP28 DAC, 1 m, NVIDIA/Mellanox-coded — $45, in stock at Resilient Tec
- MCP1600-C003 compatible — 100G QSFP28 DAC, 3 m, NVIDIA/Mellanox-coded — $92, in stock at Resilient Tec; for a switch a few rack units away
- QSFP-100G-CU1M compatible — 100G QSFP28 DAC, 1 m, Cisco-coded — $38.95, in stock at Resilient Tec
- CAB-Q-Q-100G-1M compatible — 100G QSFP28 DAC, 1 m, Arista-coded — $38, in stock at Resilient Tec
- MMA1B00-C100D compatible — 100G QSFP28 SR4 transceiver, NVIDIA/Mellanox-coded — $94, in stock at Resilient Tec; for fiber runs, test before you build on it
- MCP1650-V00AE30 — 200G QSFP56 DAC, 0.5 m — $84, in stock at Resilient Tec; Spark-to-Spark or to a 200G card
Not sure your switch will accept the cable? Send us the switch model and port type and we will confirm the coding before you order.
A 100G NIC for the NAS Side
For the NAS link described above, the storage server needs its own 100GbE QSFP port:
- MCX516A-CDAT (refurbished, $329.95): ConnectX-5 Ex, dual 100GbE, PCIe 4.0.
- MCX623106AN-CDAT (refurbished, $849.95): ConnectX-6 Dx, dual 100GbE, PCIe 4.0.
- MCX713106AS-CEAT (refurbished, $1,349): ConnectX-7, dual 100GbE, PCIe 5.0, the same ConnectX-7 generation as the Spark's own network chip.
Sold by Resilient Tec at resilient-tec.com. Genuine NVIDIA/Mellanox, lifetime warranty, shipping from Knoxville, Tennessee. Prices checked October 22, 2026.
In a PCIe 3.0 server, a single-port card such as the MCX515A-CCAT (refurbished, $169.95) uses all the bandwidth the slot has.
NAS on an older PCIe 3.0 server? Here is why one 100G port is the right size.
You Might Also Need
- DAC cable no link? — fixing 25G/100G FEC mismatches
- mlxlink and mst field guide — reading a ConnectX link that won't come up
- GB10 stuck at 100 Gb/s? — when the 200G link only gives you half
- Is the DGX Spark being discontinued? — what NVIDIA says, and where RTX Spark fits
- Why does the same transceiver work in one switch and not another? — vendor coding explained
Sources
- NVIDIA Developer Forums — No 100G connection with UACC-OM-QSFP28-SR4 modules
- NVIDIA Developer Forums — Can a DGX Spark and AGX Thor connect using QSFP cables?
- NVIDIA Developer Forums — Mellanox QSFP breakout
- NVIDIA DGX Spark User Guide — ConnectX-7 networking
- NVIDIA — Connect Multiple DGX Spark through a Switch (playbook)