Can't SSH into Vagrant VM (without using vagrant ssh)

In preparation for adapting the fabric deployment script for use by a local Vagrant VM, I'm trying to convince the VM to let me SSH into it without using SSH vagrant ssh. I keep getting errors.

I've tried many different combinations of settings, but here are the latest Vagrant files:​​​

Vagrant.configure(2) do |config|

  config.vm.provider "virtualbox" do |v|
    v.memory = 6144
    v.cpus = 2
    v.name = "mb_vagrant"
  end

  config.vm.box = "ubuntu/trusty64"

  config.vm.network :private_network, ip: "192.168.33.10"

  config.ssh.forward_agent = true

  config.vm.provision :shell, path: "bootstrap.sh"
  config.vm.network :forwarded_port, host: 8001, guest: 8001

end

vagrant ssh-configshow me:

Host default
  HostName 127.0.0.1
  User vagrant
  Port 2222
  UserKnownHostsFile /dev/null
  StrictHostKeyChecking no
  PasswordAuthentication no
  IdentityFile /Users/sloan/code/vagrant/.vagrant/machines/default/virtualbox/private_key
  IdentitiesOnly yes
  LogLevel FATAL
  ForwardAgent yes

If I try to SSH with the set key file and IP, the connection is refused:

> ssh -i /Users/sloan/code/vagrant/.vagrant/machines/default/virtualbox/private_key -p 2222 [email protected]
ssh: connect to host 192.168.33.10 port 2222: Connection refused

If I try the same method [email protected]instead of the [email protected]host key verification fails.

What am I missing here?