CSS 432
Program 4: Domain Name Service
Professor: Munehiro Fukuda
Due date: See the syllabus

1. Purpose

2. Algorithm

1. Use main( )'s argv[1] argument as an IP port to which spoofcheck.cpp should bind itself.
2. Instantiate a TCP socket.
3. Go into an infinite while( ) loop where:
   1. Accept a new connection from a client through accept( ).
   2. Fork a child process. The parent closes this connection and goes back to the top of the while( ) loop, whereas the child continues checking the integrity of this connection.
   3. Retrieve the client's IP address and port of this connection through getpeername( ).
   4. Retrieve the client's hostent data structure through gethostbyaddr( ) .
   5. Retrieve the client's official name, aliases, and registered IP addresses from the hostent.
   6. Decide whether this client is a honest or a spoofing client by matching its IP address retrieved from getpeername( ) and those retrieved from gethostbyaddr( ). (In other words, if you confirm that the client's IP address of this connection matches one of the addresses listed in hostent, you can trust this client.)
   7. Terminate this child process.

[css432@uw1-320-20 hw4]$ ./spoofcheck 12345
client addr = 216.186.75.3 port = 39329
official hostname: perseus.uwb.edu
alias: none
ip address: 216.186.75.3 ... hit!
a honest client

client addr = 216.186.75.144 port = 4252
official hostname: uw1-331-pc01.uwb.edu
alias: none
ip address: 216.186.75.144 ... hit!
a honest client

client addr = 216.186.72.14 port = 32848
official hostname: metis.uwb.edu
alias: metis
ip address: 216.186.72.14 ... hit!
a honest client

^c
[css432@uw1-320-20 hw4]$ 

3. Required Data Structures and Functions

1. getpeername( ): gets the name of the peer socket. The first argument is the socket you have accepted from a client. The second and third arguments are struct sockeaddr_in clientAddr; and socklen_t addrLen = sizeof( chientAddr ); respectively. Note that clientAddr and addrLen are whatever you can name. The clientAddr structure includes the client's address information.
2. struct sockaddr_in: is the data structure you will receive from getpeername, (i.e., clientAddr in the above). To retrieve a client's ip address and port (in sin_addr and sin_port), use inet_ntoa( ) and ntohs( ) respectively.

   #include <netinet/in.h>
   
   struct sockaddr_in {
       short            sin_family;   // e.g. AF_INET
       unsigned short   sin_port;     // e.g. htons(3490)
       struct in_addr   sin_addr;     // see struct in_addr, below
       char             sin_zero[8];  // zero this if you want to
   };
   
   struct in_addr {
       unsigned long s_addr;  // load with inet_aton()
   };
   

3. gethostbyaddr( ): retrieves information about a given host from a DNS server. The first argument is unsigned int addr of a client IP address that can be obtained by converting its string-typed IP address into an unsigned integer through inet_addr. The second and third arguments are sizeof( unsigned int ) and AF_INET respectively. The gethostbyaddr returns a pointer to a hostent data structure.
4. struct hostent: is the data structure you will receive from gethostbyaddr( ). To retrieve the official name and aliases of a given host, access h_name and h_aliases. To retrieve the list of addresses from a DNS server, (i.e., h_addr_list[i]), use int_ntoa( ).

   #include <netdb.h>
   struct	hostent {
   	const char *h_name;	/* official name of host */
   	char	**h_aliases;	/* alias list */
   	short	h_addrtype;	/* host address type */
   	short	h_length;	/* length of address */
   	char	**h_addr_list;	/* list of addresses from name server */
   #define	h_addr	h_addr_list[0]	/* address, for backward compatibility */
   };
   

5. ntohs( ): returns the argument value converted from network to host byte order. Use this function to obtain a client's port number from cleintAddr.sin_port.
6. inet_addr( ): converts a string-typed IP address, in the standard IPv4 dotted decimal notation, to an integer value suitable for use as an Internet address. Use this function to create the first argument passed to gethostbyaddr.
7. inet_ntoa( ): converts the Internet host address specified by its argument struct in_addr in to a string in the Internet standard dot notation. Use this function to obtain a string-typed IP address from clientAddr.sin_addr and struct hostent's h_addr_list[] array.

man getpeername
man gethostbyaddr
man inet_ntoa
man ntohs
man inet_addr

4. Statement of Work

 
g++ spoofcheck.cpp Socket.cpp -o spoofcheck 

[css432@uw1-320-20 hw4]$ ./spoofcheck 12345
client addr = 216.186.75.196 port = 34433
official hostname: uw1-320-21.uwb.edu
alias: none
ip address: 216.186.75.196 ... hit!
a honest client

[css432@uw1-320-31 ~]$ telnet uw1-320-20 12345
Trying 216.186.75.195...
Connected to uw1-320-20.uwb.edu (216.186.75.195).
Escape character is '^]'.
Connection closed by foreign host.

c:\>telnet uw1-320-20 12345

1. Your server, (actually each server process) terminates a client connection. Doesn't this server-initiated TCP disconnection cause any problem?
2. If a client resides in a private address domain and thus tries to connect to your spoofcheck server through NAT, can your server verify this client's integrity?
3. If a client uses a dynamic IP address to be obtained from its DHCP server, can your server verify this client's integrity?

5. What to Turn in

6. FAQ