OpenVSwitch fails to compile due to missing ssl.h headers.

In ovsdb repo:

vagrant up

[wait...]

==> mininet: Notice: /Stage[main]/Main/Exec[Compile Open vSwitch]/returns: checking for openssl/ssl.h in /usr/local/ssl... no
==> mininet: Notice: /Stage[main]/Main/Exec[Compile Open vSwitch]/returns: checking for openssl/ssl.h in /usr/lib/ssl... no
==> mininet: Notice: /Stage[main]/Main/Exec[Compile Open vSwitch]/returns: checking for openssl/ssl.h in /usr/ssl... no
==> mininet: Notice: /Stage[main]/Main/Exec[Compile Open vSwitch]/returns: checking for openssl/ssl.h in /usr/pkg... no
==> mininet: Notice: /Stage[main]/Main/Exec[Compile Open vSwitch]/returns: checking for openssl/ssl.h in /usr/local... no
==> mininet: Notice: /Stage[main]/Main/Exec[Compile Open vSwitch]/returns: checking for openssl/ssl.h in /usr... no
==> mininet: Notice: /Stage[main]/Main/Exec[Compile Open vSwitch]/returns: checking whether compiling and linking against OpenSSL works... no
==> mininet: Notice: /Stage[main]/Main/Exec[Compile Open vSwitch]/returns: configure: error: Cannot find openssl (use --disable-ssl to configure without SSL support)
==> mininet: Notice: /Stage[main]/Main/Exec[Compile Open vSwitch]/returns: make: *** [configure-stamp] Error 1
==> mininet: Error: fakeroot debian/rules binary returned 2 instead of one of [0]