Jenkins can use a TCP port to communicate with inbound (formerly known as “JNLP”) agents. such as Windows-based agents. The port for inbound agents can be used to launch an application on a client desktop by using resources that are hosted on a remote web server. In older Jenkins releases, this was called the port for The JNLP (Java Network Launch Protocol), which is used primarily by Windows-based agents.
Other options for implenting this functionality include:
Modern versions of Windows can use SSH, which is a better option for connecting to agents in most cases.
As of Jenkins 2.217, inbound agents may instead be configured to use WebSocket transport to connect to Jenkins. In this case no extra TCP port need be enabled and no special security configuration is needed.
As of Jenkins 2.0, this port is disabled by default and you should leave this port disabled unless you have an explicit need for it. If, however, you need to use inbound TCP agents, you can enable this port in the Agents section of the Configure Global Security page. Two port options are available:
Random: The TCP port is chosen at random to avoid collisions on the Jenkins controller. The downside to randomized ports is that they are chosen during the boot of the Jenkins controller. This means that firewalls may no be able to secure a random port, which makes it difficult to manage firewall rules allowing TCP traffic.
Fixed: The port is chosen by the Jenkins administrator and is consistent across reboots of the Jenkins controller. This is the more secure option, because it makes it easier to manage firewall rules that allow TCP-based agents to connect to the controller.
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