In this appendix I cover the two most fundamental data structures in the Linux Kernel Networking stack: the sk_buff and the net_device. This is reference material that can help when reading the rest of this book, as you will probably encounter these two structures in almost every chapter. Becoming familiar with and learning about these two data structures is essential for understanding the Linux Kernel Networking stack. Subsequently, there is a section about remote DMA (RDMA), which is further reference material for Chapter 13. It describes in detail the main methods and the main data structures that are used by RDMA. This appendix is a good place to always return to, especially when looking for definitions of the basic terms.