Converged Network Adapters are server cards that pass multiple networking protocols over Ethernet cables. For organizations looking to simplify their physical and virtual networking, Converged Network Adapters (CNAs) are hard to ignore.
After all, TCP/IP isn’t the only Ethernet protocol you’ll find in a data center. Many IT departments have a need for the Fibre Channel protocol (otherwise known as Fibre Channel over Ethernet, or FCoE), even if Fibre Channel cabling is no longer around.
FCoE retains a few, important differences from other networking protocols, such as iSCSI. For instance, FCoE doesn’t lie above TCP/IP in the Ethernet protocol stack, and it’s lossless (data isn’t corrupted when transferred), giving it a performance edge for certain types of virtual and physical workloads.
But you can’t insert FCoE into your production TCP/IP network and expect it to magically function. Most TCP/IP networks aren’t lossless or configured to support FCoE’s larger frame sizes. As a result, FCoE creates a problem for the average Ethernet network interface card (NIC), because these devices probably don’t have the necessary capabilities to pass FCoE traffic without a little help.
Enter Converged Network Adapters
CNAs are one solution to this virtual networking problem. A CNA contains both a Fibre Channel Host Bus Adapter (HBA) and a standard Ethernet NIC. The CNA portion that faces the outside world looks like a traditional NIC with one or two 8P8C (sometimes called RJ45) Ethernet ports for Cat 5e or Cat 6 cables.
Once connected and properly routed, the CNA then passes traditional TCP/IP networking as well as storage traffic. What’s interesting is that the CNA can pass both types of traffic at the same time. And the CNA-equipped virtual host just sees whatever network connections that are routed.
For CNAs to function, the network must support an array of new Ethernet extensions for FCoE, such as 802.1Qbb, 802.1Qaz, 802.1Qau, and DCBX. Because CNAs run both TCP/IP and storage traffic simultaneously, the entire network generally requires the added extensions.
Converged Network Adapters: Two flavors to choose from
Today, 10 Gb hardware CNAs are generally available, although some 40 Gb CNAs are beginning to appear. Using one CNA unifies all of the TCP/IP and storage networking of an entire virtual host over a single or pair of connections, and the bandwidth necessary for that level of consolidation is usually far beyond the capacity of a 1 Gb NIC.
Virtual platforms, notably VMware vSphere 5, now include support for software FCoE adapters. Like software iSCSI adapters, these software adapters perform FCoE’s extra functions at the hypervisor layer, rather than offloading it to a special hardware device. VSphere 5’s software FCoE adapter requires NICs that support Data Center Bridging and I/O offload capabilities, which older NICs may not have.
Converged Network Adapters: The champion of network consolidation
CNAs are new tools for simplifying and consolidating physical networking. Converging storage traffic atop Ethernet allows data centers to eliminate redundant cabling, which reduces costs and management headaches. IT departments also benefit from FCoE, because Ethernet has a far greater potential for raw throughput -- both now and in the future.
Running storage and traditional networking over a single connection enables you to manage all traffic from within the networking and virtual operating systems. This setup adds layers of abstraction, which further enables virtualization optimizations.
This was first published in November 2011