CS 640 Introduction to Computer Networks

Programming Assignment 2: Routing Protocol

Please check this page for FAQs and frequent updates on instructions.
Note:
It is import for your server being able to communicate with servers created by other people under the same protocol. If your server can only communicate with servers used your program, your server probably have little chance to survive in current world. Thus, we will try to test the communication between your server and servers created by other groups in the class. TA will set up a communication between two servers. One is used your program and the other is from other groups. If your server can decode the routing update packet from other group, your server will get a mark. The more mark your server can get, the better your server is. Part of your score in this project will come from this test.

Frequently Asked Questions:

(1) You should be able to run the commands (update, step, packets,  display,  disable, crash) while the servers are running.
      Use the select( ) call and add the fd of the standard input/output as show below:

FD_ZERO(&socket_set);//clears it out
        FD_SET(sockfd,&socket_set);//places our socket into the set
        FD_SET(0,&socket_set);//add fd of standard input/output
        results = select(FD_SETSIZE, &socket_set, (fd_set *) 0, (fd_set *) 0,NULL);


(2) For sending periodic updates you will have to use setitimer( ) and  sigaction( ). Look at the man pages for usage.

• When using signact(), it may cause some problem in using select() function. If you use printf("%m\n", errno); to print out the error message, it will show "Interrupted system call".
  Please use the following code to check whether the error is caused by system interruption. If so, please just neglect it.
  result = select(...);
  if(result < 0){
  if(errno != EINTR){
  printf("Erros is not caused by system interrupt\n");
  }
  }
  

(3) Here are the topology files for the example topology. You can use them to test your code. Right click and save the files. top1.txt is for
       server 1, top2.txt for server 2 and so on. You will have to modify the IP addresses and the port numbers in the files.
top1.txt
top2.txt
top3.txt
top4.txt
top5.txt

• The topology file is complete and thus it contain the IP address and port of the server which read this topology file. You may get your IP address and port by using server ID and the server list in the toopoly file

(4) Do appropriate error checks. 

How is update work?

You must distinguish between the cost from routing protocol and the cost you have physically connected. In this project, the physical cost between two connected servers will not change unless you use update or crash command. Thus, the routing protocol will update the costs to that server according to the update packet. However, no matter how the routing cost change, your reserver needs to remember the direct linked neighbors and their cost.

        3
     2----4
   7/ \3
   /     \
  1---- 3
       3

Here I gave a simple example. Before I receive the update command, the data in server one should look like this. ID: the server ID, Cost: the routing cost, Via: next hup, Direct: whether is my direct neighbor, DCost: the physical cost

ID Cost Via  Direct  DCost 
1   0          1       *       0
2   6          3        *        7
3   3         3        *        3
4   10        2

I use the update command at server 1 and 2. So the physical cost of 2 will change from 7 to 3 and I check with the routing cost 6 > 3 and thus I need to update the routing cost to 3 and next hup to 2. I also need to go through my routing table to see any server is routed via 2 and their cost must also change accordingly. After the update the table should look like this

ID  Cost  Via  Direct  DCost
  1    0        1        *        0
*2    3        2        *        3
  3    3        3        *        3
*4    6        2

Similarly, when crash happens, you should do the similar update. I crash server 2 from previous example. The data in server 1 should look like this
ID  Cost  Via  Direct  DCost
  1    0         1         *        0
*2    inf        0        *        inf   3    3        3        *        3
*4    inf        0


Submission Instructions:

What to submit:

You will need to submit the source code along with the Makefile in a single tar.gz file (name it p2.tar.gz). The extracted directory p2 should contain the server code and the Makefile.
Do not submit object files, or compiled executables. The Makefile should have two rules: clean and all.

clean will delete previous .o files, executables, etc.

all should produce a single executable called server.

How to submit:

First add the following line to your .cshrc.local file if you have not done that before(located in your home directory):
    set path = ($path /s/handin/bin)

Then run the following command at the shell prompt:

    source ~/.cshrc.local

Finally, to handin your files, enter the following command:

    handin -c cs640-1 -a PA2 -d <directory>

where <directory> is the path to the directory where  p2.tar.gz is located

handin will go through the specified directory and hand in the tar ball.

Make sure both the group members submit the same code.