Dating back many years, Jenkins has supported two network discovery services (UDP multicast/broadcast and DNS multicast). When this was first implemented this may have been a reasonable way to provide useful lookup services. With modern Jenkins capabilities, networks, and security considerations, this is no longer a good mechanism. There are now other ways to accomplish the real needs and concerns with doing it this way.
With Jenkins Security Advisory 2020-01-29 these services were disabled by default because of SECURITY-1641 / CVE-2020-2100.
These should just be removed.