ULANSeN
2.5GBase-T PCIe Network Adapter RTL8125B 2500/1000/100Mbps PCI Express Gigabit Ethernet Card RJ45 LAN Controller Support PXE for Windows/Linux/MAC with Low Profile
Bottom line: The 2.5GBase-T PCIe Network Adapter RTL8125B 2500/1000/100Mbps PCI ($15.99 on Amazon as of 2026-10-06): RTL8125B chipset auto-negotiates 2500/1000/100Mbps over standard RJ45 copper; main trade-off: no ESXi 7.0 support - only ESXi 6.7 is listed.
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*Price sourced from Amazon.com. Last updated 2026-10-06. Price and availability subject to change.
Pros & Cons
Pros
- ✓ RTL8125B chipset auto-negotiates 2500/1000/100Mbps over standard RJ45 copper
- ✓ Fits any open PCIe x1, x4, x8, or x16 slot
- ✓ Low-profile bracket included for SFF and slim cases
- ✓ PXE boot plus Wake on LAN for headless and diskless builds
- ✓ Driver support spans Windows 98SE/ME/2000/XP through Win10, Linux, DOS, and macOS
Cons
- ✗ No ESXi 7.0 support - only ESXi 6.7 is listed
- ✗ unraid support is called out specifically for 6.9.2, not newer builds
- ✗ Needs a 2.5G switch or NAS at the other end to exceed gigabit
- ✗ Single RJ45 port, so no link aggregation from one card
Manufacturer description
The ULANSeN 2.5GBase-T PCIe Network Adapter brings multi-gigabit wired networking to an older desktop or a homelab box without a motherboard swap. Built on the Realtek RTL8125B controller, this PCI Express Ethernet card auto-negotiates 2500/1000/100Mbps over standard RJ45 copper, so you can pair it with a 2.5G switch or NAS and keep your existing Cat5e/Cat6 runs. It drops into any open x1, x4, x8, or x16 slot, and a low-profile bracket is included in the box for slim and SFF cases. Driver coverage is the reason this card shows up in so many retro and hobbyist builds: Windows ME, 98SE, 2000…
SpecPicks Verdict
SpecPicks scored 2.5GBase-T PCIe Network Adapter RTL8125B 2500/1000/100Mbps PCI… using a rating × review-volume × price-fit model applied to published specs and reviews across the retro networking cards category. ULANSeN's retro networking cards lineup sits within the broader category mid-tier; price and specs are the deciding factors over brand loyalty here. Judge it on the specification table and the price rather than on sentiment: check the figures that decide your use case, then put it side-by-side with two or three close alternatives in the Compare tool before clicking through.
Common buyer scenarios for retro networking cards of this kind: matching it to an existing build, replacing a failing part, or upgrading from a previous-generation equivalent. Check the spec table below against your current setup — particularly socket / form-factor / power-rating fields — and confirm compatibility on the retailer's listing before purchase. Prices and stock are set by the retailer and may have moved since this page was last updated.
Frequently Asked Questions
What chipset does this ULANSeN 2.5G card use?
It uses the Realtek RTL8125B controller, supporting 2500/1000/100Mbps auto-negotiation over RJ45.
Will it fit a small form factor or low-profile case?
Yes. A low-profile bracket is included, and the card works in x1, x4, x8, or x16 PCIe slots.
Does it work with ESXi and Proxmox?
DSM, Proxmox VE, iKuai, unraid 6.9.2, OpenWrt, and ESXi 6.7 are supported. ESXi 7.0 is not supported.
Can I PXE boot or wake this machine over the network?
Yes, the adapter supports both PXE boot and Wake on LAN.
Does it support old Windows versions for a retro PC build?
Windows ME, 98SE, 2000, XP, Vista, 7, 8, 10, Server 2003-2016, Linux, DOS, and macOS are all listed as supported.
Key Features
- Compatible for X1,X4,X8,X16，Comes with low profilce bracket
- Support PXE function an Wake on LAN
- Support DSM,PVE,ikuai,unraid6.9.2, OpenWrt ESXI6.7 (Doesn’t support ESXI 7.0)
- Freely compatible, the network card can support multiple system: Windows ME/98SE/2000/XP, Win7 / Win8 / Win10 / Vista / Sever 2003/2008 / 2012 /2016/ Linux / DOS/MAC OS
Full Specifications
| Brand | ULANSeN |
|---|---|
| Style | Classic |
| Style Name | Classic |
| Model Number | RTL8125B |
| Compatibility | Mac, Linux |
| Mfr Part Number | RTL8125B |
| Compatible Devices | Laptop |
| Hardware Interface | Ethernet |
| Item Dimensions L x W x H | 2.8"L x 1.97"W x 0.08"H |
Ready to buy?
2.5GBase-T PCIe Network Adapter RTL8125B 2500/1000/100Mbps PCI Express Gigabit Ethernet Card RJ45 LAN Controller Support PXE for Windows/Linux/MAC with Low Profile is listed on Amazon. Price, availability, shipping and returns are set by Amazon and its sellers — check the listing for current terms. SpecPicks earns a small commission on qualifying purchases — thank you for supporting independent review work.
*Price sourced from Amazon.com. Last updated 2026-10-06. Price and availability subject to change.
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