What is a converged network adapter (CNA) when we talk about network adapters? A short expert explanation with examples…

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A converged network adapter (CNA) is a single network interface device that provides the functionality of both a Fibre Channel (FC) host bus adapter (HBA) and a TCP/IP Ethernet network interface card (NIC)

By Robert Sheldon and Todd Erickson

CNAs connect servers to FC-based storage area networks (SANs) and Ethernet-based local area networks (LANs).

A CNA attaches to a server via a Peripheral Component Interconnect Express (PCIe) interface. The server uses the CNA to send both the SAN and LAN traffic over a single connector to an Ethernet port on a network switch that can handle both types of traffic.

The CNA, a Dell Broadcom 57810S Dual-Port 10GbE SFP+ CNA as an example here, uses FC over Ethernet (FCoE) to transmit the data to the switch. The FCoE protocol enables FC communications to run directly over Ethernet, making it possible to transmit FC traffic across high-speed Ethernet infrastructure. For the LAN data, the CNA uses an enhanced version of the Ethernet protocol to ensure lossless data transmission, which is required to support the embedded FC data.

The switch that connects to the CNA must be able to carry both the Ethernet and FCoE traffic. The switch might be referred to as an FCoE switch, converged switch, access switch or forwarder switch, or it might go by another name, depending on its type and function. Regardless of its role or label, the switch converts the FCoE traffic to native FC and sends it to the SAN. It also forwards the Ethernet traffic directly to the LAN.

In SAN and LAN networks without CNAs, each server requires at least two adapters: an HBA to connect the server to the SAN and an Ethernet NIC to connect the server to the LAN. Using a single CNA on each server results in fewer adapter cards, cables, switch ports and PCIe slots. Not only does this reduce infrastructure costs, but it also reduces administrative overhead because there are fewer connections and cables to manage, leading to further cost savings.