docker - failed to set link up: address already in use

Noticed the following error message while trying to bring up Docker DTR container.

FATA[0003] Error response from daemon: subnet sandbox join failed for "10.1.0.0/24": vxlan interface creation failed for subnet "10.1.0.0/24": failed to set link up: address already in use  
I went on a wild-goose chase trying to figure out who was using 10.1.0.0/24. It turns out that it was caused due to the 4789 UDP port conflict that VXLAN uses.

Both Docker overlay and Contiv overlay use VXLAN and use the same port. In this specific scenario Contiv was already using port 4789, and so the failure was seen while configuring a docker overlay network.

Takeaway: The error message should probably be enhanced to point out the port conflict.