A converged network adapter (CNA) is a single piece of hardware that combines two traditionally separate adapter cards into one: a network interface card (NIC) for standard Ethernet traffic and a host bus adapter (HBA) for storage traffic. Instead of installing one card to connect a server to the local network and another to connect it to a storage network, a CNA handles both jobs through a single adapter with fewer ports, fewer cables, and lower power consumption.
CNAs are designed for data centers where servers need fast, reliable connections to both storage systems and regular network resources. They achieve this by using a protocol called Fibre Channel over Ethernet (FCoE), which wraps storage commands inside standard Ethernet frames so everything can travel over one wire.
What a CNA Replaces
To understand why CNAs exist, it helps to know what came before them. Servers in a data center typically need two kinds of connections. The first is a standard network connection for things like web traffic, application data, and communication between servers. A NIC handles this using Ethernet. The second is a storage connection, usually to a storage area network (SAN). A Fibre Channel HBA handles this, connecting the server to a Fibre Channel switch over fiber optic cable.
Each of these adapters takes up a slot on the server’s motherboard, requires its own cable, and plugs into its own dedicated switch. Multiply that across hundreds or thousands of servers in a data center, and you end up with a massive amount of hardware, cabling, and switch ports to manage. A CNA collapses both functions into a single card with a single port type, cutting the adapter count, cable runs, and switch ports roughly in half.
How FCoE Makes It Work
The key technology behind a CNA is Fibre Channel over Ethernet. FCoE takes the exact same storage commands that would normally travel over a dedicated Fibre Channel link and encapsulates them inside Ethernet frames. The storage protocol itself remains unchanged. It’s simply riding on a different physical connection. As the Storage Networking Industry Association describes it, FCoE places the Fibre Channel protocol on a new physical link rather than reinventing it.
This matters because Fibre Channel is a lossless protocol. It cannot tolerate dropped packets the way regular web browsing or email can. Standard Ethernet was never designed to guarantee delivery of every single frame. To bridge this gap, CNAs and their connected switches use a set of Ethernet extensions collectively called Data Center Bridging (DCB). These extensions include priority-based flow control, which prevents the switch from overwhelming the adapter with more data than it can handle, and enhanced transmission selection, which reserves bandwidth for storage traffic so it doesn’t get crowded out by regular network data.
The result is that a CNA can carry regular Ethernet traffic and storage traffic simultaneously on the same physical connection, with the storage traffic getting the lossless treatment it requires.
Hardware Offload vs. Software
One of the main advantages of a physical CNA is that it offloads protocol processing from the server’s main CPU. Handling FCoE encapsulation, flow control, and storage commands in dedicated hardware on the adapter frees up processor cycles for the applications the server is actually running. This is especially important in busy data center environments where CPU resources are at a premium.
It’s also possible to do FCoE in software, using a regular Ethernet NIC and a software initiator that handles the protocol work. This approach works, but it consumes server CPU resources that a hardware CNA would not. For smaller deployments or testing environments, a software approach can be practical. For production data centers handling heavy storage workloads, a dedicated CNA with hardware offload is the standard choice.
Port Speeds and Connections
Modern CNAs typically support 10 Gbps and 25 Gbps Ethernet speeds, with some models supporting 40 Gbps and 50 Gbps. Marvell’s FastLinQ 41000 series, for example, offers models ranging from 10GbE with standard RJ45 copper connections to 25GbE using SFP28 optical or direct-attach copper cables. Most CNAs use a PCIe interface to connect to the server’s motherboard, and they come with either one or two ports per card.
The connection type depends on the model. Some use RJ45 copper ports familiar from standard networking, while others use small form-factor pluggable (SFP) optical ports for longer cable runs or higher speeds. Dual-port models are common because they allow redundant connections to two separate switches, protecting against a single point of failure.
Switch Requirements
A CNA doesn’t work in isolation. The switches it connects to must also support FCoE and Data Center Bridging. This is a critical implementation detail that’s easy to overlook. The top-of-rack switch needs to have priority-based flow control enabled, along with the other DCB features, on every port facing a CNA. Without these settings properly configured, storage traffic can experience severe performance problems because the lossless guarantees Fibre Channel depends on won’t be in place.
In a typical deployment, the CNA connects to an FCoE-capable switch at the top of the server rack. That switch then separates the traffic: Ethernet data continues to the regular network, while Fibre Channel data gets forwarded to the storage network. Some switches handle this conversion natively, acting as a bridge between the converged Ethernet link and a traditional Fibre Channel SAN.
Who Makes CNAs
The CNA market is dominated by a handful of vendors focused on data center networking. Broadcom offers a wide portfolio of enterprise-grade adapters. Marvell (which acquired QLogic) focuses on high-speed data center solutions. NVIDIA (through its Mellanox acquisition) specializes in high-bandwidth, low-latency adapters for demanding workloads. Cisco, Dell, and HPE also offer CNAs, often optimized for tight integration with their own server and switch ecosystems.
When a CNA Makes Sense
CNAs deliver the most value in data centers that already run Fibre Channel storage networks and want to simplify their infrastructure without abandoning their existing storage investments. The consolidation benefits are straightforward: fewer adapter cards per server, fewer cables, fewer switch ports, and lower power and cooling demands across the facility. For organizations running hundreds of servers, those savings compound quickly.
If your environment uses iSCSI for storage instead of Fibre Channel, a CNA is less relevant. iSCSI already runs over standard Ethernet, so a regular NIC (or an iSCSI HBA with its own offload engine) handles both network and storage traffic without needing FCoE. CNAs are specifically solving the problem of merging Fibre Channel and Ethernet onto a single wire, which only matters if Fibre Channel is part of your storage strategy.