TEL-AVIV UNIVERSITY אוניברסיטת תל-אביב הפקולטה להנדסה FACULTY OF ENGINEERING בי"ס להנדסת חשמל School of Electrical Engineering TCP/IP IMPLEMENTATION PROJECT NUMBER: 14-1-1-816 FINAL REPORT AUTHOR TOM MAHLER 029234402 ADVISOR: PROF. PATT-SHAMIR TEL AVIV UNIVERSITY LOCATION IN WHICH THE PROJECT WAS DONE: ALGORITHMS LAB, ROOM 210, SOFTWARE BUILDING, ENGINEERING FACULTY, TEL AVIV UNIVERSITY Abstract The purpose of this project is to provide a simple C++ implemented of a full TCP/IP (layer 3 and layer 4 of the OSI model) stack for educational purposes. The project expanded to also include layer 2, layer 1 and layer 5 thus resulting in the creation of a full networking operating system that I call "inet_os". The implementation is based on the 4.4BSD-Lite2 [1] distribution, a UNIX based operating system, which is implemented in C. Using C++ instead of C was a huge step, however necessary in order to better implement the code, and provide a cleaner implementation. Figure 0.1: inet_os, top view This figure shows the relations between the layers, under inet_os. Incoming data arrives from the NIC module, which pass it upwards to Layer 2 (Ethernet), Layer 3 (IP), Layer 4 (TCP), Layer 5 (sockets) which can pass the data to an application. Note that the ARP module is not part of the OSI module and acts as a side layer for a specific purpose: resolving network address. 1 Table of Contents ABSTRACT ................................................................................................................................................. 1 TABLE OF CONTENTS ................................................................................................................................ 2 TABLE OF FIGURES ................................................................................................................................... 4 1 INTRODUCTION............................................................................................................................. 6 2 CODE REVIEW OF EXISTING DESIGNS........................................................................................... 7 2.1 4.4BSD LITE [3] .......................................................................................................................... 7 2.2 FREEBSD .................................................................................................................................... 9 2.3 OBJECT ORIENTED PROGRAMING................................................................................................... 10 3 THEORETICAL BACKGROUND ..................................................................................................... 11 3.1 LAYER 0: THE WIRE .................................................................................................................... 11 3.2 LAYER 1: NETWORK INTERFACE CARD ............................................................................................. 11 3.3 LAYER 2: ETHERNET .................................................................................................................... 11 3.4 THE ADDRESS RESOLUTION PROTOCOL ........................................................................................... 12 3.5 LAYER 3: IP ............................................................................................................................... 13 3.6 LAYER 4: TCP ............................................................................................................................ 14 3.6.1 The 3-Way Handshake ..................................................................................................... 14 3.6.2 TCP State Machine ........................................................................................................... 15 3.6.3 TCP Timers [16] ................................................................................................................ 16 3.6.4 TCP Options [16]............................................................................................................... 18 3.6.4.1 Window Scale Option .................................................................................................................. 19 3.6.4.2 Timestamp Option ....................................................................................................................... 19 4 IMPLEMENTATION ...................................................................................................................... 21 4.1 THE INET_OS ........................................................................................................................... 21 4.2 LAYER 1: NETWORK INTERFACE CARD ............................................................................................. 23 4.2.1 The NIC_Cable and the L0_buffer Classes ............................................................. 25 4.3 LAYER 2: ETHERNET .................................................................................................................... 27 4.4 THE ADDRESS RESOLUTION PROTOCOL ........................................................................................... 28 4.5 PROTOCOLS ............................................................................................................................... 30 4.6 LAYER 3: IP ............................................................................................................................... 31 4.7 LAYER 4: TCP ............................................................................................................................ 32 4.8 LAYER 5: SOCKETS ...................................................................................................................... 34 4.9 ADDITIONAL DETAILS................................................................................................................... 36 4.10 DEBUGGING .............................................................................................................................. 36 2 5 TESTING AND USE CASES ............................................................................................................ 37 5.1 BASIC USE CASE ......................................................................................................................... 38 5.2 RESOLVING AN IP ADDRESS USING ARP .......................................................................................... 40 5.3 OPENING A TCP CONNECTION USING THE TCP 3-WAY HANDSHAKE .................................................... 41 5.4 SENDING A SMALL PACKET USING TCP ........................................................................................... 42 5.5 SENDING A LARGE PACKET USING TCP ........................................................................................... 43 5.6 CLOSING A TCP CONNECTION ....................................................................................................... 47 5.7 SHUTTING DOWN A TCP CONNECTION ........................................................................................... 49 5.8 COMBINED TEST: UNRELIABLE AND DELAYED CHANNEL ..................................................................... 52 5.9 APPLICATION USE CASE ............................................................................................................... 58 5.9.1 Part 1: ARP ....................................................................................................................... 59 5.9.2 Part 2: Connecting to the Server ...................................................................................... 60 5.9.3 Part 2: Chatting through the Server ................................................................................. 61 5.9.3.1 Automatic Port Assigning Under User Privileges ......................................................................... 62 5.9.4 Part 3: Closing the connection ......................................................................................... 63 5.10 CWND FALL TEST ........................................................................................................................ 64 5.11 ADVERTISE WINDOW GETS FULL ................................................................................................... 65 6 SUMMARY, CONCLUSIONS AND SUGGESTIONS FOR FUTURE WORK ....................................... 66 7 BIBLIOGRAPHY ............................................................................................................................ 67 8 APPENDIX .................................................................................................................................... 71 8.1 THE SOURCE CODE ..................................................................................................................... 71 8.2 THE SITE ................................................................................................................................... 73 8.3 THE PDF DOCUMENTATION ......................................................................................................... 73 3 Table of Figures FIGURE 0.1: INET_OS, TOP VIEW ...................................................................................................................... 1 FIGURE 2.1: VARIOUS BSD RELEASES WITH IMPORTANT TCP/IP FEATURES .............................................................. 8 FIGURE 2.2: THE DEVELOPMENT OF BSD .......................................................................................................... 9 FIGURE 3.1: TRADITIONAL ETHERNET FRAME STRUCTURE [7] .............................................................................