  IP networks with a hybrid control plane deploy a distributed routing protocol
like OSPF and the centralized paradigm of SDN in parallel. The advantages and
disadvantages of a hybrid control plane have already been extensively discussed
in the literature. This paper examines to what extent hybrid SDN/OSPF can solve
the IP traffic matrix and related monitoring problems, inherent to the IP
layer. The problem persists in hybrid networks, as the required SDN byte
counters for a complete traffic matrix may not be sufficiently implemented (or
even not at all), or the deployed SDN nodes may be too few, or not adequately
located in the network. For such cases, we propose to augment the SDN traffic
statistics with SNMP-based measurements on IP backup links. We address
implementation and network function virtualization aspects of the required
hybrid monitoring infrastructure and discuss the timing issues of the
measurements based on hands-on experiences in our lab. We furthermore provide a
placement algorithm for SDN nodes and backup links that can guarantee a
complete IP traffic matrix.
