The port an Avocent/Vertiv DSView server uses to authorize a KVM session against the appliance the user is connecting to.
IANA registers 3871 as avocent-adsap, "Avocent DS Authorization". In Vertiv's DSView management software the server opens a TCP connection to the managed KVM or serial-console appliance on 3871 to authorize a user's session to a target device; appliances such as the AutoView switches expose it as the ADSAP2 port in their on-board web interface, where it can be turned off. You see it on data-centre KVM-over-IP switches, console servers, and rack appliances.
Do not expose
This is out-of-band infrastructure: the appliances it fronts give console and keyboard access to servers, so both the appliance and 3871 belong on an isolated management network.
$ nc -vz TARGET 3871Seen this on your network? Beige Box scans your Wi-Fi and shows every open port on every device — and its Ports tool links straight back here.
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Corrections or a missing port? Reply @rimrocksystems.