Mellanox ConnectX-5 Ex 100GbE Dual-Port QSFP28 (MCX516A-CDAT)
Two 100GbE QSFP28 ports, 200Gb/s aggregate, on a PCIe 4.0 x16 host interface. This is the card that makes 100G storage fabric and GPU-node interconnect affordable in the used market — and the reason a 10G-to-100G jump now costs less than a 10G-to-25G jump did three years ago. Tested and shipped from Hong Kong.
Fully Tested & Documented · Hong Kong Warehouse Stock · Worldwide Shipping 3–7 Days · 1-Year Warranty
Hardware Gallery
The ConnectX-5 Ex 100G, Up Close
ConnectX-5 Ex 100G — Dual QSFP28, PCIe 4.0 x16
Two QSFP28 cages at 100GbE each. The PCIe 4.0 x16 host interface is the point of this card: on a PCIe 4.0 slot it can actually feed 200Gb/s, where an x8 card cannot. On a PCIe 3.0-only server it will negotiate down and you will not see rated throughput — check your slot generation first.
Heatsink, Bracket and Firmware Revision
A 100G dual-port card dissipates real heat and is passively cooled by design, so it needs a server chassis with directed airflow across the card length. We photograph the heatsink and bracket and record the firmware revision per card, so what arrives is what you planned for.
2×100G
QSFP28 Ethernet ports
200Gb/s
aggregate port bandwidth
PCIe 4.0
x16 host interface
$159
used entry price, Sep 2026
Key Specifications
| Component | Specification |
|---|---|
| Adapter | Mellanox ConnectX-5 Ex 100GbE dual-port QSFP28 network adapter |
| Part Number | MCX516A-CDAT |
| Ports | 2 × 100GbE QSFP28 (Ethernet SKU; the VPI variant MCX556A-EDAT adds EDR InfiniBand — this listing is not the VPI part) |
| Host Interface | PCIe 4.0 x16 |
| Network Offloads | RDMA over Converged Ethernet (RoCE), SR-IOV, overlay/tunnel offloads |
| Form Factor | PCIe adapter with full-height bracket |
| Cooling | Passive heatsink — requires server chassis airflow |
| Condition | Pre-owned / refurbished tested pulls |
ConnectX-5 Ex 100G is where the used market stopped being a compromise: at $159–$280 you are buying a card whose new-equivalent price was several times that, and the bandwidth puts it in a different class from anything on 25G. The practical constraint is the host, not the card — this needs a PCIe 4.0 x16 slot to deliver its rated throughput, which means a current-generation platform. It is a natural fit for our PowerEdge R750 and NVIDIA L4 pages, where the card's job is feeding storage or carrying GPU traffic. If your servers are still PCIe 3.0, read our R740xd page and consider the ConnectX-5 25G instead — plugging a 100G card into an x8 PCIe 3.0 slot is a common and expensive mistake.
Transparent Pricing
2026 Reference Pricing by Configuration
Tracked live in the September 2026 collection round — nine asking-price data points. This is the widest spread in the batch and the spread is real, not noise: the low end and the high end are different cards to different sellers.
Pre-Owned ConnectX-5 Ex 100G (MCX516A-CDAT)
$159–$280
Nine listings tracked: $159.00, $179.98, $239.00, $245.00, $258.36, $267.90, $268.00, $279.86, $279.99 — median ≈$258. Note the shape of the data: one listing at $159, one at $180, then a solid cluster from $239 to $280. That $159–$180 pocket is worth asking about, but treat it as opportunistic stock rather than a market price you can plan a fleet purchase around.
New / Sealed Retail
On Request
No new-stock price range is published here: the September 2026 collection round returned pre-owned and open-box listings only. We will quote new or sealed stock against live availability on request rather than publish an uncollected figure.
Asking prices, not transaction prices — volume deals typically close 5–15% below asking. Nine data points, pre-owned listings. Source channel: eBay, sorted by price+shipping, lowest first (first-screen listings). Collected Sep 20, 2026. This entry corresponds to section 38 (Mellanox ConnectX-5 Ex 100G, MCX516A-CDAT, dual-port QSFP28) of the HKCHL used-server price index.
Origin
Hong Kong Warehouse
Free port — full export documentation
Transit
3–7 Days Air Freight
Tracked, insured, worldwide
Warranty
1-Year Warranty
Diagnostic report in every box
Quality Process
What We Test Before a ConnectX-5 Ex 100G Ships
Part Number and Firmware Verification
On-card part number, PSID and firmware revision read and recorded per card. On a 100G card the firmware generation materially affects performance, so we log it rather than quote a generic 'latest'.
100G Link-Up on Both Ports
Each QSFP28 port brought up at 100GbE against a reference switch, tested individually. A port that only links with a specific optic or only at 40G is a fault, not a configuration nuance.
PCIe Link Width and Generation Check
The card's negotiated PCIe width and generation are read on the bench, not assumed from the label. A card that trains at x8 instead of x16 will not deliver 200Gb/s, and you would rather learn that from us than from a benchmark.
RoCE / RDMA Throughput Test
RDMA between two hosts with throughput and error counters checked. RDMA is the reason to buy ConnectX-5 Ex over a generic 100G NIC, so it gets verified rather than assumed.
Sustained-Load Thermal Logging
Both ports driven under sustained traffic with heatsink temperature logged. These cards are passively cooled and depend on chassis airflow — we confirm they hold up in a server, not on a desk.
Report in the Box
Every unit ships with its per-machine diagnostic report and warranty. Full process: inspection guide.
Frequently Asked Questions
What does a used Mellanox ConnectX-5 Ex 100G cost in 2026?
Nine pre-owned listings tracked in September 2026 spanned $159 to $280 with a median of about $258. The distribution matters more than the range here: there were only two listings below $240 and then a dense cluster between $239 and $280, so the realistic planning price for a fleet purchase is closer to $250 than to $160. HKCHL quotes against live stock and will tell you straight which end of the band you are actually buying at.
Do I need PCIe 4.0 to use a ConnectX-5 Ex 100G?
You need it to get the rated performance, and this is the single most common mistake with this card. The MCX516A-CDAT is a PCIe 4.0 x16 card delivering up to 200Gb/s aggregate. In a PCIe 3.0 x16 slot it will still work but the host link becomes the bottleneck, and in a PCIe 3.0 x8 slot it is worse still — you may end up paying for 100G and running closer to 25G. If your servers are PCIe 3.0 generation (R740xd, DL380 Gen10 and similar), the ConnectX-5 25G is the honest recommendation. Tell us your server model and we will confirm slot generation before quoting.
How does ConnectX-5 Ex 100G compare with ConnectX-5 25G on price per gigabit?
Compare them properly and the CX-5 Ex looks strong on paper: $159–$280 for 200Gb/s aggregate against $99–$130 for 50Gb/s is roughly three to four times the bandwidth for around twice the price at the median. But that comparison only holds if you can use the bandwidth. Add the cost of 100G switching, QSFP28 cabling and PCIe 4.0 servers, and the total system cost gap is far larger than the card price gap. Buy the CX-5 Ex when the fabric around it is already 100G; buy the CX-5 when it is not.
What cabling and optics does the MCX516A-CDAT need?
QSFP28 cages accept 100G QSFP28 DAC for short in-rack runs and 100G optical modules with matched fibre for longer reaches. Worth knowing: QSFP28 cages will also take 40G QSFP+ and, with the right breakout cable, present as 4× 25G — which is how most people connect a 100G card to a 25G leaf switch. Tell us the switch and the distance and we will quote the correct cable or breakout rather than leave you to guess.
Does this card work with NVIDIA/Mellanox drivers on Linux and VMware?
Yes — ConnectX-5 Ex is driven by the standard Mellanox OFED stack on Linux and by the inbox or vendor-supplied driver on VMware and Windows Server. We test with the current release at the time of shipping and record the firmware revision on the card, so you know what you are starting from. If your platform has a firmware-pinning requirement, tell us and we will check the card against it before it ships.
Are refurbished 100G network cards tested before shipping?
Yes — and 100G cards get the most thorough bench of anything we sell. Each card goes through a part-number and firmware read, per-port 100G link-up on both ports, a PCIe negotiated-width and generation check, an RDMA/RoCE throughput test between two hosts, and sustained-load thermal logging. Cards ship with the test result noted and carry a 1-year warranty.
Get a Current ConnectX-5 Ex 100G Quote
Send us your server model, slot layout and target quantity. We will confirm MCX516A-CDAT availability against live stock, verify that your platform can actually feed the card, and quote the cabling or breakout to match — as well as the ConnectX-5 25G alternative if your fabric is not ready for 100G. Ships worldwide from Hong Kong.
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