The link is up at 1000/full with no errors: the cable and the socket are fine. The switch reaches the
DHCP server, and the trunk does carry VLANs 10 to 40: the core has nothing to do with it, and in fact the
neighbours (Gi1/0/12, Gi1/0/15) are working. On the other hand, show running-config interface Gi1/0/14 shows
switchport access vlan 40 and the description CAM-COULOIR-B: socket B-14 was used by the camera
removed on Friday. Salma's PC therefore landed in VLAN 40 CAMERAS (its MAC is learned there),
where no DHCP serves workstations: Windows fell back to an APIPA 169.254.x.x address.
Incident resolved
Analysis and fix
Fix (in configuration mode):
configure terminal
interface Gi1/0/14
description BUR-B14
switchport access vlan 20
end
write memory
Then, on the PC: ipconfig /renew → address in 10.20.0.x. Check: show interfaces status,
show mac address-table interface Gi1/0/14 (MAC learned in VLAN 20).
To keep it from coming back:
- keep a patching plan up to date (wall socket → port → VLAN → use) and review it before any office move;
- when a device is removed, put the port back into a known state: the offices' default VLAN,
or better, a “parking” VLAN with no access, and
shutdown; - keep accurate port descriptions: here, “CAM-COULOIR-B” gave the answer in one line;
- in the long run, 802.1X authentication (or dynamically assigned VLANs) prevents a port from keeping a frozen assignment.