IANA allocated Docker port: 2375

2375/2376 are assigned:
http://www.iana.org/assignments/service-names-port-numbers/service-names-port-numbers.xhtml?search=docker

https://github.com/dotcloud/docker/issues/1440
Merge pull request #378 from SvenDowideit/iana-port-change

IANA allocated Docker port: 2375