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Overlay networking
This is the most important part of the cloud ecosystem. These are secondary networks that run over the underlay network in a transparent manner.
The reason for the existence of the overlay network is the diversity and uncommon programming/configuration standard of the underlay. If a technology such as OpenFlow is implemented and available, then the overlay network may not be needed and both of them might collapse into one.
The overlay network is implemented by using two major technologies:
- GRE - Generic Routing Encapsulation
- VLAN and VxLAN- Virtual LAN and Virtual Extensible LAN
While GREs have been implemented for a long time on physical routers and switches on the WAN side of the overlay to create the required logical topology on the physical links, on the LAN/data center side of the network, these networks are mainly implemented using virtual network devices - such as virtual switches in the hypervisor.
Let's take a look at the technologies before we discuss their usage in a hybrid cloud scenario.