A technician runs show interfaces terse on a subscriber-aggregation switch and finds a port listed as down, even though a colleague swears the fiber patch and optic on that port were both replaced and tested earlier that day. What should the technician check first before assuming a new physical fault has appeared?

A terse interface listing reports the current operational state without explaining why a link is down, and an interface intentionally taken out of service with a disable statement produces the same down status as a genuine physical failure, so checking whether the port was administratively disabled is a fast, non-invasive first step that rules out a configuration cause before assuming new hardware trouble, especially right after other engineers have been actively working the same equipment. A climbing CRC error counter describes a link that is up and passing traffic but corrupting some frames along the way, which is a different symptom entirely from a port reported fully down, and there's no link at all on a down interface to be accumulating that counter against. OSPF hello timer settings live above the physical link and can't make an interface itself register as down in a terse listing, since a link has to already be up before OSPF can even attempt an adjacency over it. A duplicate IP address produces intermittent reachability or ARP disputes on a link that is otherwise up, not an interface-down status. A caveat worth remembering is that administrative status should be the first thing eliminated precisely because it's the cheapest thing to check and the easiest to overlook after someone else has recently touched the device. An operational check is confirming whether the interface's configuration stanza contains a disable statement before sending a technician back out for another physical inspection.