"keyserver timed out" despite disabled firewall

Question

Trying to add keys in a Ubuntu 14.04 virtual machine using a makefile, but I keep running into an error, although I've tried several tricks like switching to port 80 or disabling firewall.

root@vm0083:~# make -f install_tools_and_libs.mk all
    for i in '51716619E084DAB9'; do echo "PUB_KEY: $i"; sudo apt-key adv --recv-keys --keyserver hkp://keyserver.ubuntu.com $i; done
    PUB_KEY: 51716619E084DAB9
    Executing: gpg --ignore-time-conflict --no-options --no-default-keyring --homedir /tmp/tmp.DAavGLrJ4i --no-auto-check-trustdb --trust-model always --keyring /etc/apt/trusted.gpg --primary-keyring /etc/apt/trusted.gpg --keyring /etc/apt/trusted.gpg.d/ansible-ansible.gpg --keyring /etc/apt/trusted.gpg.d/fkrull-deadsnakes.gpg --keyring /etc/apt/trusted.gpg.d/puppetlabs-keyring.gpg --keyring /etc/apt/trusted.gpg.d/puppetlabs-nightly-keyring.gpg --keyring /etc/apt/trusted.gpg.d/x2go-stable.gpg --recv-keys --keyserver hkp://keyserver.ubuntu.com 51716619E084DAB9
    gpg: requesting key E084DAB9 from hkp server keyserver.ubuntu.com
    gpg: keyserver timed out
    gpg: keyserver receive failed: keyserver error
    make: *** [add_pub_key] Error 2

I'm not familiar with the public keys system, any idea what's wrong? I've used that same makefile successfully before in Ubuntu 14.04 in Virtual Box.

Solution

Looks like it is a problem related to a firewall blocking port 11371 or something like this. Anyway, I found a workaround here.

gpg --keyserver hkp://keyserver.ubuntu.com:80 --recv-keys E084DAB9
gpg -a --export E084DAB9 | sudo apt-key add -