The core network is the primary site where application servers are located. Most organizations now have a combination of dedicated application servers alongside servers configured for hosting virtual servers, usually running VMware ESXi. The older servers tend to have multiple Gigabit Ethernet connections, so the core network switches are similar to the Cisco 6500 or a stack of Cisco 3750 Gigabit switches, with 50-300 Gigabit Ethernet ports total.

New servers are shipping with 10 Gb Ethernet on the motherboard, and the price for 10 Gb Ethernet cards has dropped so much that 1 Gb for servers is becoming difficult to cost justify. Especially since 10 Gb connections in the datacenter can be made with copper twinax cabling, it is difficult to make the decision to purchase anything else.

The core network upgrade can all be done independently of the access layer upgrade. If an organization has a large layer 3 switch like the Cisco 6500 or a stack of Cisco 3750's at the core of their current network, the Nexus 5000 can be connected in with multiple 10 Gb Ethernet connections, providing the lowest cost upgrade while still retaining the core network upgrade performance benefits. For larger core networks, the Cisco Nexus 7000 can be used to provide a larger quantity of 10 Gb links to multiple Nexus 5000 switches.

The access layer switches are used for workstation connectivity and are also used to power 802.11N wireless access points, 1 Gb IP phones, and Ethernet powered thin clients. In addition to high speed wireless, the access layer has to accommodate Voice, Video, and Virtual Desktop Infrastructure. For all these requirements, the access layer switches have to have more than just raw bandwidth. They also need to be:

Secure - with voice, video, and desktop sessions on the LAN, the switches must have security features that can prevent them from getting attacked with MAC address floods, rogue DHCP servers, gratuitous ARP's changing the default gateway, and other attacks that can be launched by malware. This security must be implemented at the switch level.

Reliable - Long Mean Time Between Failure, well tested code to limit bugs, good support from the manufacturer in case there is a software or hardware issue.

Power Density- Switches have to be able to support the power density of the planned devices. Most switches can not power all ports at the highest levels, so it is important to calculate the expected power load of the switches and specify the correct ones.

The distribution layer is where all the access layer uplinks come together. Most of the organizations tend to have a large main campus with an extensive LAN. Many of them have a LAN that is set up in a fashion similar to the Cisco High Availability LAN designs of a few years back. This is 100 Mb Ethernet at the access layer and multiple1Gb fiber uplinks to the core/distribution switches. The larger networks have multiple distribution switches and separate core switches , but most mid-size organizations have the collapsed core/distribution model.

The Nexus 7000 enters the discussion when an organization considers upgrading the fiber uplinks on the access layer switches from 1 Gb to 10Gb Ethernet. As soon as an organization internalizes the need for 1Gb access layer switches and 10Gb uplinks, the place where these uplinks all come together has to be upgraded as well.