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) |
+----------------------------------+