Finding conflicting information online. Looks like Cisco Nexus switches are cut-through by default and can be changed. Also looks like IOS switches are store-and-forward by default and some can be changed and some can't (like a 3750 switch).
Can someone shed some light on this please? Thanks.
Best Answer
I'm not aware of any IOS switches that can be set to cut-through. My impression was that they were all store-and-forward. As an example, a quick google search reveals cisco pages that state fixed store-and-forward behavior for 3750-X and 3560-X, 2960 and 2960-S, etc. I think the reasons for this are two-fold. First, ASICs have sped up switches so much that any gains from cut-through are small. And second, Cisco switches are purchased at least in part due to their wide range of features - many of which probably require reading the whole frame. Certainly, QoS requires store-and-forward, as well as, I would expect, layer 3 security features.
I also saw the documentation that you probably did regarding the Nexus switches. Their intended use is very different than the typical IOS based switch. They are used in server farms that require high bandwidth, low latency connections among the servers, storage area networks, and other data center elements. So it is expected that the very low latency gains do help in some of these scenarios, while advanced security and QoS type features are occurring at the edge of the data center rather than in the middle of it where cut-through is useful.