There is a such a thing as an Ethernet tap (basically, you tap one pair to Rx on a NIC, and if you want both ways you need another NIC)... but it's tricky to av

There is a such a thing as an Ethernet tap (basically, you tap one pair to Rx on a NIC, and if you want both ways you need another NIC)... but it's tricky to avoid impedance mismatch etc, and not feasible at all for Gigabit Ethernet. The simple/easy option is configure port mirroring on your switch[1] as mentioned by other commenters. [1] https://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst2960/software/release/12-2_55_se/configuration/guide/scg_2960/swspan.html https://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst2...