Before recabling a server you must administratively disable the interface eth0, leaving the device present in the kernel so it can be brought back with a single command afterwards. Which iproute2 command does that?

LPIC-1 Exam 102-500, objective 109. Networking fundamentals medium

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The options

Correct ip link set dev eth0 down

Correct. The link object controls the layer-2 state of a device, and `set dev eth0 down` clears the IFF_UP flag. The device, its addresses and its driver stay in place, so `ip link set dev eth0 up` restores it.

Not correct ip addr flush dev eth0

Wrong. This removes the IP addresses configured on eth0 but leaves the link administratively up, so the interface still carries traffic at layer 2 and can still be autoconfigured.

Not correct ip link delete eth0

Wrong. Deleting a link destroys a virtual device such as a VLAN, bridge or tunnel. On a physical NIC the kernel refuses the operation, and where it succeeds the device is gone rather than merely down.

Not correct ip route flush dev eth0

Wrong. This purges routing table entries whose output device is eth0. Traffic that has another matching route still leaves through the interface, which remains up and addressed.

Why

iproute2 splits interface handling across objects: `ip link` for the device and its layer-2 state, `ip addr` for the addresses bound to it, and `ip route` for the forwarding entries that point at it. Bringing a device down is a link-level operation, so it is `ip link set dev NAME down`, the modern equivalent of `ifconfig eth0 down`. A downed interface keeps its IPv4 addresses, which become active again when the link is set up; IPv6 addresses are dropped on link-down unless keep_addr_on_down is set.

Where this comes from

Cited
manual page ip-link(8)

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