I've confirmed that the IO Crest, full-length, dual-port, 2.5GbE mPCIe card works out of the box on nodes 1 and 2 with both CM4 and RK1 SoMs running Ubuntu. The attached photos came from the RK1 u-boot, Ubuntu lspci and Ubuntu ifconfig. On Amazon, the part number is SI-MPE24079. There is also a half-length, single-port version of this card, the SI-MPE24073. IO Crest sells these cards through their AliExpress store as the IO-MPE8125B-2GLAN (dual-port) and IO-MPE8125B-GLAN (single-port). It looks like the dual-port card is no longer available, but the single-port card is available for under $20USD. Sorry, I don't have a way to test performance and stability at the moment. As time and my knowledge allows, I'll try to set up an RK1 to pxe or tftp boot from the card. https://cdn.discordapp.com/attachments/1220245484376162304/1220245484581421066/u-boot_pci-mPCIe_dual_port_2.5Gb_Ethernet_adapter.jpg?ex=661777aa&is=660502aa&hm=8ec8ab2f20f04e0427bf342f3f93adcff901e068da4e93e16e2ecdc9be3c358e& https://cdn.discordapp.com/attachments/1220245484376162304/1220245484862574592/ubuntu_lspci_mPCIe_dual_port_2.5Gb_Ethernet_adapter.jpg?ex=661777aa&is=660502aa&hm=b6e66a97a1dfbb6ab3d4ce162b72698d1668dc79004d0a4a8f7cbd2d0b44ed0e& https://cdn.discordapp.com/attachments/1220245484376162304/1220245485160497172/ubuntu_ifconfig_mPCIe_dual_port_2.5Gb_Ethernet_adapter.jpg?ex=661777aa&is=660502aa&hm=ddb7e25ade93d49e326cfec99b8b575bf355036eb0208d7375dab9c577f4303a&

@rkalra (see above)

I've ordered an IO Crest single-port, 2.5Gb, half-length mPCIe card from Amazon. I don't expect any issues, but this should allow some basic performance testing with an Ethernet crossover cable. I'll probably order a second dual-port card to test NIC bonding, round-robin performance and path failover.