1. Raw Sockets

2. What are Raw Sockets? Allows you to bypass the TCP/UDP layers.
Send/receive your own packets, with your own headers.
You need to do all protocol processing at user-level.

3. Typical Uses ICMP messages Routing protocols Hacking
ping generates ICMP echo requests and received ICMP echo replies.
Routing protocols
gated implements OSPF routing protocol.
Uses IP packets with protocol ID 89 – not supported by kernel.
Hacking
Generating your own TCP/UDP packets with spoofed headers

4. sockfd = socket(AF_INET, SOCK_RAW, proto)
Raw socket creation
Only root can open a raw socket.
sockfd = socket(AF_INET, SOCK_RAW, proto)
where proto is IPPROTO_RAW, IPPROTO_ICMP etc.

5. Raw socket output As usual – sendto(), sendmsg() etc.
IP_HDRINCL option
Specifies whether the process or the kernel builds the IP header.
/* allow process to build IP header */
int on=1;
setsockopt( sockfd, IPPROTO_IP, IP_HDRINCL, &on, sizeof(on))

6. Raw socket input Normally using recvfrom()
Conditions for a packet to match raw socket
If protocol parameter was specified, only packets with that protocol value are delivered.
If bind() was called on raw socket, only packets destined to bound IP address are delivered.
If connect() was called, only packets from connected address are delivered.

7. Which protocol types are delivered?
TCP and UDP never reach raw sockets
Kernel IP stack handles these
Linux implementation is an exception.
All ICMP except
ICMP echo request
Timestamp request
Mask request
All IGMP
All other protocols that kernel doesn't understand
Such as OSPF

8. Exercise Write a simple “Hello” exchange program using raw sockets
that implements your own protocol
on top of IP.

9. Java Reference Book - “Thinking in Java” by Bruce Eckel
Book is online at

10. Object oriented languages
Levels of abstraction
Abstracting the
problem as
object interactions
Object oriented languages
(C++, Java)
Imperative languages
(C, FORTRAN, ALGOL)
Abstracting the
machine model
Assembly language
Low-level
machine details
Machine

11. Object An object has State (internal data)
Behavior (methods that operate on data)
Identity (object can be addressed uniquely)

12. Objects… Class defines properties of a set of similar objects.
Think of it as type of the object
Protection boundaries define what object state is visible to others.
Inheritance allows a new class to inherit properties of an earlier class without re-defining them.
Interface defines what requests others can make to a particular object

13. Parent class 
Interface 
Child classes 

14. Primitive Data types boolean - false char - ‘\u0000’ (null)
byte - (byte)0
short - (short)0
int - 0
long - 0L
float - 0.0f
double -0.0d

15. Creating a class class Circle { } public :
Circle(int x, int y, float r) {…}
void draw(){…}
void erase(){…}
void move(){…}
private :
int x_;
int y_;
float radius_; }
Methods
Fields

16. Creating an object Circle c = new Circle(10,20,5); c.draw(); c.move();
c.erase();

17. Inheritance abstract class Shape { public : Shape(int x, int y) {
x_ = x;
y_ = y; }
abstract void draw();
abstract void erase();
abstract void move();
protected :
int x_;
int y_;

18. Inheritance… class Circle extends Shape { Circle(int x,int y,float r){
super(x,y);
radius_ = r; }
void draw() {…}
void erase(){…}
void move(){…}
protected :
float radius_;

19. Inheritance… class Square extends Shape { Square(int x,int y,float w){
super(x,y);
width_ = r; }
void draw() {…}
void erase(){…}
void move(){…}
protected :
float width_;

20. void doStuff(Shape s) {
s.erase();
// ...
s.draw(); }
Circle c = new Circle();
Square s = new Square();
Line l = new Line();
doStuff(c);
doStuff(s);
doStuff(l);

21. Interfaces interface DrawObject { } // automatically public
void draw();
void erase();
void move();
// Compile-time constant:
int SOME_CONST = 5; // static & final }

22. class Shape { public : Shape(int x, int y) { x_ = x; y_ = y; }
protected :
int x_;
int y_;

23. class Circle extends Shape implements DrawObject{
Circle(int x,int y,float r){
super(x,y);
radius_ = r; }
void draw() {…}
void erase(){…}
void move(){…}
protected :
float radius_;

24. class Square extends Shape implements DrawObject{
Square(int x,int y,float w){
super(x,y);
width_ = r; }
void draw() {…}
void erase(){…}
void move(){…}
protected :
float width_;

25. static members
static fields or methods have one instance across all object instances
class X {
static int i = 0; …… }
x1 = new X();
x2 = new X();
x1.i++;
x2.i++;
System.out.println(“Result = “ + x2.i);
 Result = 2

26. final member/class final class X { class X {… }
Final classes cannot be extended.
class X {
final int m();
Final methods cannot be overridden.
int mthd(final MyClass mc) {…}
Final arguments cannot be modified.
final int MY_CONST = 10;
Final fields/references are constants

27. Things you should learn from TIJ
Packaging your classes - Chapter 5
Java I/O system - Chapter 11
Error handling with exceptions - Chapter 10
Applets - Chapter 14

28. Using Standard Java Packages
java import java.lang.*;
public class HelloDate {
public static void main(String[] args) {
System.out.println("Hello, it's: ");
System.out.println(new Date()); }

29. Some other packages… java.net java.rmi java.io java.applet java.awt
java.math