The ability to avoid disasters is improved by distributing physical compute and network resources between data centers that are geographically distributed over long distances. Geographic distribution provides higher elasticity and almost unlimited flexibility of the resources required to dynamically deploy VM loads.
The network side can transparently support distributed applications by extending Layer 2 between multiple sites. Yet by definition, the Layer 3 traffic carried between users and active applications through the cloud does not have native knowledge of the physical IP device locations, other than the network prefix given through the most significant bit-group of the IP address. The IP subnet is a logical visible subdivision of the network that is usually limited to the local network. It therefore delimits its broadcast domain defined by the system mask. The IP subnet is usually established by the enterprise or service provider network team. In general, an IP subnet addresses a set of IP equipment that belongs to the same VLAN.
Traditionally, if an IP subnet or a VLAN is associated with a physical location inside a data center, with the concept of interconnecting cloud resources, the broadcast domain is stretched over the distances that separate the data centers (DCI theoretically can be established up to unlimited distances with L2 over L3 transport). Therefore, the concept of location induced natively by the IP subnet subdivision loses one of its original functions of localization.
Thus, depending on the distance between the remote sites, the native routing mechanism can have an impact on performance for three major types of communication.
- Traffic from the user to the server
- Traffic from the server to the user
- Traffic from server to server (such as in a multi-tier application)
