The COPS channel a cable policy server uses to install QoS gates on a CMTS under PacketCable Multimedia.
IANA registers 3918 as pktcablemmcops. In a PacketCable Multimedia deployment an application manager asks a policy server for bandwidth on a subscriber's cable modem, and the policy server pushes that decision to the CMTS as a COPS Gate-Set message; Cisco's CMTS documentation states plainly that COPS sessions on PCMM use TCP port 3918 by default. This is distinct from PacketCable DQoS, which uses a different port. You will only find 3918 inside a cable operator's network, between policy servers and CMTS routers.
Do not expose
Whoever can speak COPS to this port can allocate QoS on a subscriber's service — an operator control plane that must stay inside the operator's own network.
$ nc -vz TARGET 3918Seen 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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