Virtual networking 101: bridging the gap to understanding TAP

This post details the technical intricacies of Linux TAP devices, explaining their functionality, setup, and performance tuning. It covers the `tun/tap` interface, device creation via `ioctl` and `/dev/net/tun`, flag options like `IFF_TAP`, `IFF_NO_PI`, and `IFF_VNET_HDR`, and the role of `IFF_NAPI`. It also delves into buffer size management (`txqueuelen`), `virtio_net_hdr` structure, and offloads like `TUN_F_CSUM`, `TUN_F_TSO4`, and `TUN_F_TSO6`, providing practical code examples and insights into potential performance bottlenecks and kernel behaviors.