This lecture will be a very basic introduction to the FreeBSD networking stack. We will see the mbuf, which is the main data structure used by FreeBSD for packet handling, and look at how it handles incoming and outgoing packets. The lecturet can serve as a general basic introduction for unix kernels networking, and will (I hope) be of interest not only to people planning to work in the FreeBSD kernel (which I guess are not that many).
If by any chance, someone is interested in a more in depth understanding of the FreeBSD kernel, I will be happy to help.
FreeBSD_kernel_networking.pdf, FreeBSD kernel networking.sxi