There's no such thing as a "data center network." In truth, there are several networks in the data center that interact with and overlap each other.

Of course, there is the data network, over which the servers communicate for most purposes, and with clients outside the data center, and that is what most people mean when they speak of the data center network.

Even that, though, is not really a single network - it relies on two other networks: the data-center-to-branch network, and the data-center-to-data-center network. Enterprise IT services reach the majority of users over data-center-to-branch networks, running on T-1 or T-3 or even network-to-network VPNs over the Internet. IT uses DC-to-DC nets, running over SONET rings or MPLS or direct fiber runs, to do things like distribute loads among resource pools or maintain business-continuity preparedness via storage replication or even virtual-server state replication.

Within the data center there are other networks as well. Most prominently and commonly, there is the storage-area network, running on Fibre Channel (FC). The FC SAN represents a second web of connectivity, linking servers to the data center’s central storage, as well as linking storage devices like NAS heads and tape libraries and RAID arrays to each other. It has high bandwidth and high reliability - one of the primary qualities of the SAN is that it does not drop data packets.

In some data centers, another network overlays or partially replaces the data and FC storage nets: the high-performance fabric. Some use a system like Myrinet to interconnect the nodes in a cluster, enabling low-latency, high-bandwidth data sharing among systems. Others use InfiniBand for such interconnects, or to connect servers to peripherals for very high-speed I/O.

Lastly, there is one more kind of network found in most data centers: a management network. The management net comes in two flavors, sometimes both found in the same data center. The traditional management net links servers’ serial console ports (and keyboard and mouse ports) to a management appliance, which provides KVM console access to connected systems and sometimes layers other management features on top of console sharing.

The newer management net is Ethernet, like the data network, but parallel to it and confined to the data center. This separate network provides many of the benefits of traditional KVM access, especially if connecting to a remote-management card in a server, but more often works as a complement to KVM by supplying dedicated, out-of-band access to the servers for management, monitoring, or provisioning systems.