Linux How to Check Which NIC is Onboard eth0 or eth1 Ubuntu Centos Debian Mint

So say you happen to have 2 NICs of the exact same chipset, they will generally show up as the same name, with possibly a different revision in lspci. Normally this is not an issue if you have a server with 4 NICs, generally the eth0 to eth3 appears from left to the right (or right to left on some vendors) so it doesn't take much figuring out.

Generally if you have different chipsets for different NICs, it should be easy to know which one is eth0 or the first NIC in the OS.

In our case below eth0 will be the 01:00.0 PCI device but this doesn't help since we don't know which one is the onboard one or which one is the second one plugged into the motherboard by PCI x4

01:00.0Ethernet controller: Realtek Semiconductor Co., Ltd. RTL8111/8168/8411 PCI Express Gigabit Ethernet Controller (rev 15) 02:00.0 Ethernet controller: Realtek Semiconductor Co., Ltd. RTL8111/8168/8411 PCI Express Gigabit Ethernet Controller (rev 11)

Solution Just use lscpi -v which will often reveal it in the DeviceName

As you can see for the 02:00.0 device below, the DeviceName is "Onboard Realtek LAN". This is important if you are creating a device that needs to be on different networks. Also note that many often assume that the Onboard NIC will always be eth0 but in the case we show that the onboard NIC is eth1 and the add-on NIC was eth0 which is unexpected for some.

01:00.0 Ethernet controller: Realtek Semiconductor Co., Ltd. RTL8111/8168/8411 PCI Express Gigabit Ethernet Controller (rev 15) Subsystem: Realtek Semiconductor Co., Ltd. TP-Link TG-3468 v4.0 Gigabit PCI Express Network Adapter Flags: bus master, fast devsel, latency 0, IRQ 16 I/O ports at e000 [size=256] Memory at 81304000 (64-bit, non-prefetchable) [size=4K] Memory at 81300000 (64-bit, non-prefetchable) [size=16K] Capabilities: [40] Power Management version 3 Capabilities: [50] MSI: Enable- Count=1/1 Maskable- 64bit+ Capabilities: [70] Express Endpoint, MSI 01 Capabilities: [b0] MSI-X: Enable+ Count=4 Masked- Capabilities: [d0] Vital Product Data Capabilities: [100] Advanced Error Reporting Capabilities: [140] Virtual Channel Capabilities: [160] Device Serial Number Capabilities: [170] Latency Tolerance Reporting Capabilities: [178] L1 PM Substates Kernel driver in use: r8169 Kernel modules: r8169 02:00.0 Ethernet controller: Realtek Semiconductor Co., Ltd. RTL8111/8168/8411 PCI Express Gigabit Ethernet Controller (rev 11) DeviceName: Onboard Realtek LAN Subsystem: Acer Incorporated [ALI] RTL8111/8168/8411 PCI Express Gigabit Ethernet Controller Flags: bus master, fast devsel, latency 0, IRQ 19 I/O ports at d000 [size=256] Memory at 81200000 (64-bit, non-prefetchable) [size=4K] Memory at a0000000 (64-bit, prefetchable) [size=16K] Capabilities: [40] Power Management version 3 Capabilities: [50] MSI: Enable- Count=1/1 Maskable- 64bit+ Capabilities: [70] Express Endpoint, MSI 01 Capabilities: [b0] MSI-X: Enable+ Count=4 Masked- Capabilities: [d0] Vital Product Data Capabilities: [100] Advanced Error Reporting Capabilities: [140] Virtual Channel Capabilities: [160] Device Serial Number Capabilities: [170] Latency Tolerance Reporting Kernel driver in use: r8169 Kernel modules: r8169