vpp packages need to depend on specific versions of each other. Failure to do so can cause upgrades from previous vpp versions to fail.

Example:

If you have installed the release 16.06, and you add the vpp master apt repo and then

apt-get install vpp vpp-dpdk-dkms

Which should upgrade to the newest versions... the old version of vpp-lib is not upgraded, and so vpp fails on startup due to missing symbols. This is because while vpp depends on vpp-lib, it does not specify which version and so any installed version suffices.