Netstack is a userspace TCP/IP network stack and interfaces with zircon network drivers. Netstack serves as a back-end for fdio socket API.
+-----------+ +-----------+ | FIDL app | | POSIX app | +------+----+ +-----+-----+ | | +-------v----------------+ | | FIDL network service | | | (//garnet/bin/network) | | +-------+----------------+ | | | +-----v----------------------v---+ | BSD socket API | | (//zircon/system/ulib/fdio) | +---------------+----------------+ | +-------------v--------------+ | netstack | | (//garnet/go/src/netstack) | +-------------+--------------+ | +----------------v-----------------+ | Ethernet driver | | (//zircon/system/udev/ethernet) | +----------------------------------+