For proper flow of data packets through any IP network, the learning of MAC addresses and IP routes is imperative. Traditional networks use MAC learning on the data path and IP routes are exchanged using specific protocols. Most modern SDN platforms are designed to work multi-vendor physical network devices. Additionally, they are required at times to support virtual networks without the data packets being examined by the underlying physical network. Therefore, the flow of packets in SDN platforms is an important concept to understand.
Overlay network traffic (between VM instances of the same virtual network) is encapsulated and carried across the cloud network. This is needed to provide isolation between different tenant networks.
OpenContrail supports the following encapsulation methods:
MPLS over GRE
VXLAN
MPLS over UDP
We will cover MPLS over GRE in a bit more detail, since that is the default setting for OpenContrail...