So we (Apache Traffic Server) have our Jenkins CI system behind a proxy, naturally. This works very well. We have a few remote slaves, that uses the "local" Java start processes, and when they fetch the .jnpl file, the destination host and port for it to talk to Jenkins itself is wrong. It (of course) tries to talk to the proxy host, which doesn't work! This was fairly easy to fix, in the Node configuration for the slaves, click the advanced option, and add a host:port value for "Tunnel connection through".