Dual Port 2.5G PCIe Network Card — RTL8125B

Model: PR25R21  |  2× RJ45  |  PCIe x4 / x8 / x16  |  Windows / Linux / macOS

Add two 2.5 Gigabit Ethernet ports to any desktop, server, or workstation with a spare PCIe x4, x8, or x16 slot. The PR25R21 uses the proven Realtek RTL8125B chipset — widely supported across Windows, Linux, and macOS with no manual driver install required on most modern systems.

Who is this for?

• NAS builders — dual 2.5G ports for link aggregation or separating management and storage traffic
• Homelab / Proxmox / pfSense — reliable, well-supported NIC with wide hypervisor compatibility
• Gaming PCs — upgrade from 1G for noticeably faster local network transfers
• Small servers — supports VLAN tagging, jumbo frames, and IEEE 1588 time sync

Key features

• 2× 2.5Gbps RJ45 ports — backwards compatible with 1G and 100M networks (auto-negotiation)
• PCIe x1 electrical, x4/x8/x16 physical — fits in any full-size PCIe slot; uses only x1 lanes so no bandwidth wasted
• PCI Express 2.1 — backwards compatible with PCIe 1.x and 3.x motherboards
• Jumbo frames up to 16K bytes for large file transfers
• VLAN support — IEEE 802.1Q tagging and 802.1ad double VLAN
• IEEE 1588v1/v2 & 802.1AS time synchronisation
• Energy Efficient Ethernet (IEEE 802.3az) — lower power when link is idle
• Hardware ECC & CRC — on-chip error correction for data integrity
• MSI / MSI-X interrupt support — lower CPU overhead than legacy INTx
• Supports standard and low-profile brackets

OS compatibility

• Windows — driver included in Windows 10 / 11; older versions may need manual install
• Linux — in-kernel r8169 / r8125 driver; works out of the box on most distributions
• macOS — supported (driver may be required depending on version)
• Also compatible with Proxmox, TrueNAS, pfSense/OPNsense, ESXi (community driver)

Full specifications

Model	PR25R21
Chipset	Realtek RTL8125B
Interface (physical)	PCIe x4 / x8 / x16 slot
Interface (electrical)	PCIe x1 (Gen 2.1)
Output ports	2× RJ45
Transmission rate	2.5 Gbps (also 1G / 100M auto-negotiation)
Jumbo frames	Up to 16K bytes
VLAN	IEEE 802.1Q, 802.1ad (double VLAN)
Time sync	IEEE 1588v1, 1588v2, 802.1AS
OS support	Windows, Linux, macOS
Operating temp	0°C to 70°C
Storage temp	−10°C to 80°C
Bracket	Standard + low profile (both included)

In the box

• 1× PR25R21 dual-port 2.5G PCIe network card
• Low-profile bracket

Good to know

• The card is electrically PCIe x1 — it slots into x4, x8, or x16 physically but only uses one lane. Your other PCIe lanes are unaffected.
• To reach 2.5 Gbps your switch, router, or other device must also support 2.5GbE (NBASE-T). Connecting to a 1G switch will link at 1 Gbps.
• RTL8125B driver is included in Linux kernel 5.9+ and Windows 10/11 — plug and play on most modern setups.
• Not a server-grade Intel or Mellanox NIC — this is a cost-effective workstation/homelab card suited to non-critical workloads.