Consul's HTTP API and web UI — the port most people mean when they say "Consul".
IANA registers 8500 as fmtp, EUROCONTROL's Flight Message Transfer Protocol, from 2003; almost every listener you will actually meet is Consul, whose documentation lists 8500 as "The HTTP API". That API serves the service catalog, the key/value store, health checks and the built-in web UI, and it is unauthenticated unless ACLs are explicitly enabled. It travels with 8300, 8301/8302 and 8600 on a Consul server. A quick GET of /v1/status/leader identifies it in one request.
Do not expose
With default (ACL-less) configuration this API hands out the whole catalog and KV store, and accepts writes. Bind it to a private address, turn on ACLs and TLS, and reach it over a VPN.
$ curl -s http://TARGET:8500/v1/status/leaderSeen 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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