The switch and router terminology distinction has become fairly meaningless at enterprise level hardware as discussed in that comment. The same corporate access or top-of-rack "switch" is just as capable of layer 3 routing as it of layer 2 network handling. This happened because the desire to expand a layer 2 fabric across multiple physical switches basically reinvented a lot of layer 3 concepts on layer 2. The silicon is the same for both, just different algorithms.
There are multiple motivations and resulting technologies there:
- “L3 Switches”, which in essence are routers that do not have discrete ports and instead have closely coupled switch. Alternatively the same thing can be viewed as switch with powerful enough control-plane CPU that it can do routing (pure L2 managed switches usually have ridiculously underpowered CPUs). This can be and often is combined with some amount of offloading the routing and even more complex upper-layer processing into hardware.
- things like Shortest Path Bridging, which uses L3-style routing protocol (IIRC it is IS-IS) in order to build L2 FIB tables for L2 switches. The idea there is to not only have (R)STP-like redundant paths for ethernet, but to use full capacity of such paths when it is available.
On the hardware level it is mostly about accelerating the fast-path, where the hardware FIB contains some cache of bit patterns seen in the received frame, where it should be forwarded and maybe how it should be rewritten. And packets that are not matched by HW FIB are passed to the CPU to be processed. In a “dumb” bridge (ie. L2 switch), such frames would be simply broadcasted to all ports.
While the general idea is the same, there is material difference in the silicon complexity between matching destination MAC of ethernet frame and matching arbitrary bit patterns somewhere in TCP header of IPv6 packet.
