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CS 779/879
Design
of Network Protocols
Spring
2005
Midterm
Exam
Time
2 & 1/2 hours
Open
Book & Notes
Name:
Unix login:
NOTE: In
order to make the programs short, you may not write any include, comments or non-essential error
statements.
The expected language is C/C++,
however you may use any other language such as java if it can do the required
task.
Question 1: (35 points)
1. Write
a client program called TCPattack with the following syntax:
TCPattack <host>
The program test each TCP port P on
<host> and if it can connect to port P, then attacks the
host by opening as many TCP connections as it can possibly have to P until it
can not make any further connections to P.
The program displays the total number of successful TCP connections to
each port P.
Solution
Question
2: (30 points)
Consider the following server programs:
1. TCPServer: create a TCP
server a server socket S and bind to a port P=1234
2. ReuseTCPServer: same as 1
but it call the reusePort function listed below on S.
3. UDPServer: same as 1 but uses UDP.
4. ReuseUDPServer: same as 2
but uses UDP.
void reusePort(int s)
{ int one=1;
if ( setsockopt(s,SOL_SOCKET,SO_REUSEADDR,(char *) &one,sizeof(one)) == -1 )
{ printf("error in setsockopt,SO_REUSEPORT \n"); exit(-1);
}
}
Explain if it is possible to
run the programs as specified, assuming port 1234 is not used by any other
programs running on isis
and cash.
1. isis % TCPServer &
cash % TCPServer
Possible Not-Possible
Why?
2. isis
% TCPServer &
isis % TCPServer
Possible Not-Possible
Why?
3. isis
% TCPServer &
isis % ReuseTCPServer
Possible Not-Possible
Why?
4. isis
% ReuseTCPServer &
isis % TCPServer
Possible Not-Possible
Why?
5. isis
% TCPServer &
isis % UDPServer
Possible Not-Possible
Why?
6. isis
% UDServer &
isis % TCPServer
Possible Not-Possible
Why?
7. isis
% UDPServer &
isis % UDPServer
Possible Not-Possible
Why?
8. isis
% UDPServer &
isis % ReuseUDPServer
Possible Not-Possible
Why?
9. isis
% ReuseUDPServer &
isis % UDPServer
Possible Not-Possible
Why?
10. isis
% ReuseUDPServer &
isis % ReuseUDPServer
Possible Not-Possible
Why?
Question 3: (35 points)
The following is
an example of select statement code (explained in our lecture: Multiplexing using select and listed in
chapter 6 of textbook).
Modify
this code (show all modifications and do not recopy the code) to such that:
1. Any message received from a
client is sent to all other clients.
2. The program exits if no
activity occurs for a period that exceeds 5 minutes.
#include "unp.h"
int
main(int argc, char **argv)
{ int i, maxi, maxfd, listenfd, connfd, sockfd;
int nready, client[FD_SETSIZE];
ssize_t n;
fd_set rset, allset;
char line[MAXLINE];
socklen_t clilen;
struct sockaddr_in cliaddr, servaddr;
listenfd = Socket(AF_INET, SOCK_STREAM, 0);
bzero(&servaddr, sizeof(servaddr));
servaddr.sin_family = AF_INET;
servaddr.sin_addr.s_addr = htonl(INADDR_ANY);
servaddr.sin_port = htons(SERV_PORT);
Bind(listenfd, (SA *) &servaddr, sizeof(servaddr));
Listen(listenfd, LISTENQ);
maxfd = listenfd; /* initialize */
maxi = -1; /* index into client[] array */
for (i = 0; i < FD_SETSIZE; i++)
client[i] = -1; /* -1 indicates available entry */
FD_ZERO(&allset);
FD_SET(listenfd, &allset);
for ( ; ; ) { rset = allset; /* structure assignment */
nready = Select(maxfd+1, &rset, NULL, NULL, NULL);
if (FD_ISSET(listenfd, &rset)) { /* new client connection */ clilen = sizeof(cliaddr);
connfd = Accept(listenfd, (SA *) &cliaddr, &clilen);
printf("new client: %s, port %d\n", Inet_ntop(AF_INET, &cliaddr.sin_addr, 4, NULL),
ntohs(cliaddr.sin_port));
for (i = 0; i < FD_SETSIZE; i++)
if (client[i] < 0) { client[i] = connfd; /* save descriptor */
break;
}
if (i == FD_SETSIZE)
err_quit("too many clients");
FD_SET(connfd, &allset); /* add new descriptor to set */
if (connfd > maxfd)
maxfd = connfd; /* for select */
if (i > maxi)
maxi = i; /* max index in client[] array */
if (--nready <= 0)
continue; /* no more readable descriptors */
}
for (i = 0; i <= maxi; i++) { /* check all clients for data */ if ( (sockfd = client[i]) < 0)
continue;
if (FD_ISSET(sockfd, &rset)) { if ( (n = Readline(sockfd, line, MAXLINE)) == 0) { /*connection closed by client */
Close(sockfd);
FD_CLR(sockfd, &allset);
client[i] = -1;
} else
Writen(sockfd, line, n);
if (--nready <= 0)
break; /* no more readable descriptors */
}
}
}
}