I am using OS X v10.10 (Yosemite) and Cisco Anyconnect (which are apparently a bad combination for using boot2docker), and the following finally worked for me (thanks to the linked GitHub issue comment):
These steps will add a port forwarding rule and modify your environment to have Docker point to 127.0.0.1 (instead of 192.168.59.103 or other NATed IP address).
First – boot2docker needs to be installed, but not running.
If it is currently running – stop it now:
boot2docker down
Add a rule to forward traffic from 127.0.0.1:2376 to port 2376 on the boot2docker vm:
vboxmanage modifyvm "boot2docker-vm" --natpf1 "docker,tcp,127.0.0.1,2376,,2376"
Start boot2docker:
boot2docker up
Set default DOCKER environment variables:
$(boot2docker shellinit)
Override the DOCKER_HOST variable to point to 127.0.0.1:
export DOCKER_HOST=tcp://127.0.0.1:2376
Now you should be able to run docker commands:
docker version