Interface went down (and its line protocol followed)
%LINK-3-UPDOWN: Interface GigabitEthernet1/0/24, changed state to down / %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet1/0/24, changed state to down
In plain English: The physical link on this port dropped.
Platform: Cisco IOS / IOS XE. Values shown are the documented defaults — confirm them on your platform with the check commands below.
What it means
The physical link on this port dropped. LINK reports the physical layer (cable, signal); LINEPROTO reports whether the port can actually pass framed traffic. They usually fall together. One down event at 2 AM is a footnote; the same pair repeating all day is a failing physical path that will eventually take something important with it.
Likely causes, in order
A cable was unplugged (check whether someone was working in that rack or office).
A failing cable, optic, or port — especially when the events repeat with no human pattern.
The device at the far end rebooting, losing power, or having its own port fail.
Loose fiber: a connector that moves when the rack door closes.
Check, in order
show logging | include Gi1/0/24Count the events and read their times. Business hours suggests a person; random times suggest hardware.
show interfaces Gi1/0/24 counters errorsCRC and input errors climbing means the physical path is degrading, not just dropping.
show interfaces statusWhether the port is down now, and what is supposed to be connected to it.
The fix
Reseat, then replace, the cable or patch lead. For fiber, clean or replace the optic and the patch lead as a pair.
Move the connection to a spare port to separate 'switch port' from 'everything beyond the switch'.
If the port serves something critical, fix the physical cause before the next event picks a worse moment.
Did this fix it for you? One tap — anonymous, nothing to type, and nothing you send is ever published.
Thanks — your tap helps the next engineer. A run of "still broken" reports sends this page back to the top of our re-check list.
Full case: this error is one stop in a bigger fault. Work the complete playbook: Port Keeps Going Err-Disabled — checks, ranked causes, the fix, and verification.