Every professional server embeds a BMC (Baseboard Management Controller) — iDRAC at Dell, iLO at HPE, XCC at Lenovo, with IPMI as the generic standard. This independent mini-computer stays reachable even with the server off or the OS crashed.
What it enables remotely: virtual console (screen and keyboard as if on site), electrical power cycling, ISO mounting for reinstalls, sensors (temperatures, PSUs), hardware logs. In colocation, it is what saves you 90% of trips and smart hands tickets.
Non-negotiable security rules: the BMC on a dedicated management network (never exposed to the Internet — BMC CVEs are regular), default passwords changed, firmware updated, and access via VPN or a bastion. Plan one copper run per server for this network in your cabling layout.