I’ve noticed that Jenkins has an unpleasant habit to listen on two UDP ports (5353 and 33848) on all interfaces even if it was told to listen on 127.0.0.1:8080.

These ports are for UDP multicast broadcast. You may not need either of them, and you can disable them by adding the following options:

-Dhudson.DNSMultiCast.disabled=true -Dhudson.udp=-1

eg.

java -Dhudson.DNSMultiCast.disabled=true -Dhudson.udp=-1 -jar jenkins.war –httpListenAddress=127.0.0.1 –httpPort=8080 –daemon –logfile=/home/jenkins/jenkins.log

See the Jenkins docs for more https://wiki.jenkins.io/display/JENKINS/Features+controlled+by+system+properties