Which command sequence forces a NIC to renegotiate?

• A. systemctl restart NetworkManager
• B. ip link set <iface> down; ip link set <iface> up
• C. ip link set <iface> down
• D. ip addr flush dev <iface>

Answer: (B)

Renegotiating a NIC happens when the physical link is reset, so the hardware can re-establish the connection and re‑negotiate speed and duplex with the switch. Bringing the interface down and then back up does exactly that: it disables the link and then re-enables it, triggering the NIC to renegotiate immediately. The two-step sequence ip link set down; ip link set up forces this re-negotiation.

Other options don’t directly reset the link state in the same way. Restarting NetworkManager can affect configuration but isn’t a reliable, immediate renegotiation trigger. Bringing the interface down alone leaves the link inactive, and flushing IP addresses affects only IP configuration, not the link parameters.