When the VPP-API is modified for a new protocol, a "chicken and egg" problem can arise because the operational CSIT test suite needs to be updated to use the new VPP-API but it cannot be validated with the existing VPP_STABLE_VER vpp image. Likewise the VPP image containing the updated VPP-API cannot be verified using the existing operational CSIT test suite.

The process of how to update CSIT & VPP in this instance needs to be documented on the CSIT wiki: https://wiki.fd.io/view/CSIT/Branching_Strategy