My universities networking lab has 2 P4 enabled networking switches. They are essentially a Intel Xeon based server, similar to how high end cumulus switches work, but the switching backplane consists of a custom ASIC, which is part that is programmed in P4.

It's an impressive technology but the driver support outside the vendor provided linux distro is so abysmal that we weren't able to integrate it for use by students (and we tried for a whole year).