Despite both companies having drawn lines in the sand when it came to the use and sales of their own competing datacenter infrastructure product there had been a tacit agreement in place to work together on the IEEE 802.1Qbg and 802.1Qbh standards designed to move much of the security, policy and management processing from the virtualized switches, currently running on server NICs, and move it back to physical Ethernet switches.
Network World is now reporting that HP is accusing Cisco of changing the scope of the standard so that a new system of tagging will be required, meaning that the two standards will no longer be interoperable on the same hardware without vendors specifically supporting both forms of tagging. Initial comments on the plans for these two standards indicated that they would be able to work together. Cisco made this choice in spite of the fact that the already agreed upon standard was VN-Tag, an existing Cisco product.
Regardless of who might be at fault here (if this can even be described this way), the difference in tagging systems is representative of the different approaches being taken by the two companies, with HP's very datacenter focused converged infrastructure model and Cisco's borderless networking approach. Cisco is defending itself by saying that the change was not their decision, but one driven by the standards committee, an excuse that HP doesn't seem to be buying.
The two vendors continue to work together on the IEEE standards but the bottom line, for now, is that there will be at least two very divergent camps for customers to consider in their future datacenter designs.