HACKING

slitch hacking howto
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Here's a tour of the program, starting with an overview of each source
file.

tcpip.lisp:
  Main logic, implementing the actual protocol stack.

switch.lisp:
  A very simple ethernet switch example program.

netlib-structures.lisp:
  Definitions of major datatypes, like protocol headers.

netlib.lisp:
  Network device abstraction with wrappers for TAP and PF_PACKET
  backends. Code for reading and writing protocol headers.

tuntap.lisp:
  This implements the tunnel device interface to the operating
  system. It has a simple interface to open and close tunnels, and
  read and write frames on them.

packet-socket.lisp:
  Interface to Linux PF_PACKET sockets. They provide raw
  ethernet-level I/O on existing network interfaces.

binary-types.lisp:
  Module for mapping binary frame formats that come off the network
  to/from Lisp structures. It's a very nice encoding and decoding
  framework. I found it on the internet, the real author is a
  norwegian bloke called Frode Vatvedt Fjeld.

binary-types-extra.lisp:
  Extensions to the binary types package which have been needed for
  TCP/IP packet formats.

binary-rw-gen.lisp:
  Alternative backend for binary-types, which is now used
  throughout. This is a small set of macros for compiling a whole
  binary type (and all its components) into a single read or write
  function.

netlib-package.lisp:
  Defines the Lisp package for netlib, exported symbols, etc.

root.lisp:
  A small program that lets you do certain operations as root (if
  correctly configured).

netlib.system, netlib.asd:
  Lisp-style makefiles. Take your pick.

Any questions can be sent to Luke Gorrie <luke@bluetail.com>.

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Literature:

You may be wondering where to get the details of all these protocols
to implement them. The definitive references are the RFCs which you
can get off the 'net. Some relevant ones are:

  0826 Ethernet Address Resolution Protocol: Or converting network
       protocol addresses to 48.bit Ethernet address for transmission on
       Ethernet hardware. D.C. Plummer. Nov-01-1982. (Format: TXT=22026
       bytes) (Also STD0037) (Status: STANDARD)

  0791 Internet Protocol. J. Postel. Sep-01-1981. (Format: TXT=97779
       bytes) (Obsoletes RFC0760) (Also STD0005) (Status: STANDARD)

  0768 User Datagram Protocol. J. Postel. Aug-28-1980. (Format: TXT=5896
       bytes) (Also STD0006) (Status: STANDARD)

  0793 Transmission Control Protocol. J. Postel. Sep-01-1981. (Format:
       TXT=172710 bytes) (Updated by RFC3168) (Also STD0007) (Status:
       STANDARD)

Note: The specification of UDP is 3 pages long. They sure knew how to
write protocols and specs back then. :-)

As a supplement, I can very happily recommend the first two volumes of
Douglas Comer's "Internetworking with TCP/IP" series. Richard Stevens'
books (TCP/IP Illustrated series) cover much the same topics and would
also be just fine.

The first volume describes how all the internet protocols work in a
very easy to follow way. As well as the basics - ARP/IP/ICMP/UDP/TCP -
it also covers routing and multicast protocols, BOOTP and DHCP, and
higher-level protocols like FTP, TELNET, NFS, etc.

The second volume is a case study of a particular (nice)
implementation of the TCP/IP protocol suite. The book is full of
source code, which is written in C and based on a novel operating
system.

If you are (or want to be) familiar with a free operating system like
Linux or FreeBSD, they should make excellent references as well.