The ConnectX-5 is a SFP28 25/100GbE adapter from Mellanox (now NVIDIA), on PCIe 3.0 x8 or x16 depending on SKU; the ConnectX-5 Ex variant adds PCIe 4.0 on its higher-speed SKUs, using the mlx5 driver that ships in the mainline Linux kernel. It is end-of-life at its maker, which means no new firmware - not that it has stopped working. 6 listings in stock, from $244.00.
Prices updated · live figures update every 4-5 hours
Passive direct-attach copper, by length. A DAC is a fixed-length cable with the transceivers moulded on - you buy the whole run at once rather than a cable plus two modules.
Every "compatible with" phrase below is the seller's own wording, recorded as a claim and badged. We have not tested any module against any switch.
| Module | Type | Brand | Seller compatibility claims | Price | |
|---|---|---|---|---|---|
| SFP28 25GBASE-SR module | 25GBASE-SR | 10Gtek | none stated | $19.99 | Buy |
| SFP28 25GBASE-SR module | 25GBASE-SR | 10Gtek | none stated | $19.99 | Buy |
| SFP28 25GBASE-SR module | 25GBASE-SR | 10Gtek | none stated | $19.99 | Buy |
| SFP28 AOC | AOC | 10Gtek | none stated | $19.99 | Buy |
| SFP28 25GBASE-LR module | 25GBASE-LR | 10Gtek | none stated | $22.99 | Buy |
| SFP28 AOC | AOC | ipolex | 25GBase Active Optical Cable, 25Gbps SFP28, SFP28-25G-AOC5Mseller claim | $31.99 | Buy |
| SFP28 AOC | AOC | 10Gtek | none stated | $35.99 | Buy |
| SFP28 AOC | AOC | 10Gtek | none stated | $37.99 | Buy |
ConnectX-5 is the card most homelab buyers land on when they decide to step past 10GbE, and the reason is the SKU spread: the same family covers 25G dual-port SFP28 cards and 100G dual-port QSFP28 cards, both on the mlx5 driver, both from listings that are almost entirely Mellanox-branded rather than third-party boards. That first-party concentration is unusual in this market and worth knowing before you shop - see the OEM note below for why.
The honest headline: NVIDIA's own documentation now calls ConnectX-5 end-of-life, the same status ConnectX-4 Lx carries in the 10GbE cluster below. That is a commercial statement about new orders, not a statement about whether the card works or is supported in the kernel you are about to install - NVIDIA's own, separately dated release notes confirm mlx5 keeps supporting it. Read both facts together rather than either alone.
The 25G and 100G SKUs are physically different cards - SFP28 cage versus QSFP28 cage - and the cabling and DAC tables on this page default to the 25G SFP28 side, since that is the more direct step up from a 10GbE SFP+ build and the connector most of our tracked listings use. A 100G QSFP28 ConnectX-5 needs QSFP28 cabling instead - see the cabling guide's QSFP28 section for those live listings, and the /networking/100gbe hub for a build priced around the 100G SKU specifically.
PCIe requirement varies by SKU rather than being one number for the whole family: base ConnectX-5 EN cards run PCIe 3.0 at x8 or x16 depending on port count and speed, and the ConnectX-5 Ex variant adds PCIe 4.0 on its 100G SKUs. Check the exact part number's PCIe line in NVIDIA's own manual before assuming a slot is wide enough - a 100G card in a physically x16 but electrically x4 slot is the category's classic expensive mistake.
NVIDIA's own Linux Kernel Upstream Release Notes (dated 2026) list mlx5 as the driver for ConnectX-5 by name, in the mainline kernel and actively maintained - the same driver family as ConnectX-4 and ConnectX-4 Lx. That matters more than any marketing claim, because a card whose driver is in the mainline kernel is a card your Linux-based NAS or hypervisor recognises without you doing anything.
We state in-kernel driver names as documented facts because they are - they come from the kernel's own driver documentation, not from a forum thread reporting that something worked. Where community experience is the only evidence available for something, we say so rather than dressing it up.
NVIDIA's ConnectX-5 user manual states plainly: "The ConnectX-5 product line has moved to end-of-life" (confirmed 2026-09-13). NVIDIA's own kernel release notes, dated the same year, still list mlx5 as actively supporting it, and NVIDIA's current DOCA-Host device list (dated September 2026) still includes ConnectX-5 - so the commercial line is closed for new orders while both the in-kernel driver and NVIDIA's current software packages keep supporting cards already in the field. Those are two different questions and conflating them is the most common error in discussions about this card.
Windows support is a separate question from Linux support and varies by card age. Check the maker's current driver page for your specific part number before buying if Windows is the target, because an in-kernel Linux driver tells you nothing about it.
Every ConnectX-5 listing we track right now is Mellanox-branded (tier 1) rather than a third-party board asserting the chipset - unlike the Intel E810 tier below, this specific card has not attracted the same third-party-board ecosystem in what we currently hold in stock. That can change as more of these get pulled from decommissioned servers.
The general shape of the crossflash question is the same across every card in this category: an OEM board carries the server maker's firmware, that firmware sometimes behaves differently from the silicon vendor's, and there is a community practice of replacing it. We link the maintained community documentation rather than reproducing the procedure here. A stale copy of a flashing guide is actively dangerous, and the people who maintain the canonical versions do so because the details change.
If you are buying an OEM-branded card specifically because it is cheaper, factor in the possibility that you will need to do this. If that prospect does not appeal, the vendor-branded card at a higher price is buying you the absence of that job.
This is a SFP28 card, so the port is a cage rather than a socket and you choose what goes in it. For two machines near each other, a passive direct-attach copper cable is the cheapest, coolest and simplest answer, and it is what most builds using this card should use.
For longer runs you need optics - a module at each end plus a fibre between them - or an active optical cable, which packages the same thing as a single sealed object. Both cost more than direct-attach copper and both go much further.
The compatibility question belongs here rather than being buried. Third-party module sellers list the equipment they claim compatibility with, and those are claims we record and badge rather than verify. Vendor coding is a documented phenomenon: cards and switches can and do refuse modules that do not identify as approved parts. A direct-attach cable avoids the entire question, which is another reason it is the default recommendation for a two-machine build.
The cabling guide covers every SFP28 DAC, AOC and optic in one place · The 25/40/100GbE hub compares every card in this cluster and the switched-versus-point-to-point arithmetic · 10GbE vs 25GbE is the step-up decision, priced both ways · used servers almost always have a spare PCIe slot for one · NAS devices is usually what sits at the other end · rack disk shelves are the other common thing on the far end of a fast link.
For most home and homelab builds, yes - the EOL status is commercial (no new firmware or hardware revisions from NVIDIA), while the mlx5 driver keeps this card supported in the mainline Linux kernel per NVIDIA's own current release notes. Treat it the same way the site treats the ConnectX-3 and ConnectX-4 Lx: sound for a machine you expect to rebuild within a few years, a longer-horizon gamble for one you want to leave untouched for a decade.
Physically different connectors - SFP28 for the 25G SKUs, QSFP28 for the 100G ones - on the same mlx5 driver and the same EOL status. They need different cables. This page's cable tables default to SFP28; a 100G QSFP28 build needs the cabling guide's QSFP28 section instead.
mlx5, confirmed by name in NVIDIA's own Linux Kernel Upstream Release Notes, dated 2026 - current documentation, not an old snapshot. The same page confirms mlx5 covers ConnectX-4 and ConnectX-4 Lx too, so troubleshooting knowledge mostly transfers across the family.
It depends on the exact SKU - base EN cards run PCIe 3.0 x8 or x16, and the ConnectX-5 Ex variant adds PCIe 4.0 on its 100G SKUs, per NVIDIA's own manual. Check your specific part number rather than assuming, and check the slot's electrical width (not just its physical size) before buying a 100G card for it.
Not in what we currently track - every listing we hold right now is Mellanox-branded. That is unusual for this market and may simply reflect current stock; check the live table above rather than assuming it stays that way.
Both, as of NVIDIA's current documentation: it's in NVIDIA's DOCA-Host supported-device list (dated September 2026) as well as the in-kernel mlx5 driver. That puts it ahead of the standard (non-Lx) ConnectX-4, which the same DOCA-Host list does not include.
Specification claims on this page were checked against the pages below on 4 August 2026. Where a widely-repeated figure did not survive that check, we report what the source says now and say so in the text rather than repeating the familiar number.