CS352 - Extracting IP addresses from responses - Solved

This is a medium difficulty project. This will serve as the foundation for the upcoming programming projects. A working client code is given to you in Client.py; this is the same client as project 0.  Your job, like project 0, is to write the corresponding server code. The goal of the server is to reply to any client with the IP address of any domain name sent to it. 

 

 

The server is not allowed to use gethostbyname or any similar function designed to do DNS. Instead, the server must send a UDP message to the Google DNS server at 8.8.8.8 and ask it for the IP address. This means the server will need two sockets, one server socket to talk to the client and one client socket to talk to the Google DNS server. You must construct this DNS message according to your knowledge of the protocol and the provided resources. Lastly, it should then close gracefully when the client is done sending domain names. Sample output and input files have also been provided. Note that due to certain aspects of the way DNS works, your output may not exactly match the sample; you can check if it worked by typing the IP address into your browser and making sure you get the right webpage.

 

 

If the DNS server at 8.8.8.8 sends many answers, send all of them back to the client separated by a ‘,’ character in the order that they were sent to you. If the answer is not an A record, you may simply return the string ‘OTHER’ once per a non-A answer instead of an ip address.

 

Here is a diagram of the header from the RFC (if these diagrams confuse you read the routly blog post from the resources).

 

                                    1  1  1  1  1  1

      0  1  2  3  4  5  6  7  8  9  0  1  2  3  4  5

    +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+

    |                      ID                       |

    +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+

    |QR|   Opcode  |AA|TC|RD|RA|   Z    |   RCODE   |

    +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+

    |                    QDCOUNT                    |

    +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+

    |                    ANCOUNT                    |

    +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+

    |                    NSCOUNT                    |

    +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+

    |                    ARCOUNT                    |

    +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+

 

and the question looks like:

 

                                    1  1  1  1  1  1

      0  1  2  3  4  5  6  7  8  9  0  1  2  3  4  5

    +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+

    |                                               |

    /                     QNAME                     /

    /                                               /

    +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+

    |                     QTYPE                     |

    +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+

    |                     QCLASS                    |

    +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+

 and the answer:

                                    1  1  1  1  1  1

      0  1  2  3  4  5  6  7  8  9  0  1  2  3  4  5

    +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+

    |                                               |

    /                                               /

    /                      NAME                     /

    |                                               |

    +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+

    |                      TYPE                     |

    +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+

    |                     CLASS                     |

    +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+

    |                      TTL                      |

    |                                               |

    +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+

    |                   RDLENGTH                    |

    +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--|

    /                     RDATA                     /

    /                                               /

    +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+-

 

 

Please do not assume that all programs will run on the same machine or that all

connections are made to the local host.  We reserve the right to test your

programs with local and remote socket connections, for example with Client.py,

And Server.py each running on a different machine. You are welcome to

simplify the initial development and debugging of your project, and get off the

ground by running all programs on one machine first. However, you must

eventually ensure that the programs can work across multiple machines.

 

 

The programs must work with the following command lines:

 

 

python Server.py PORT

python Client.py SERVERADDRESS PORT

 
By default the client reads from a file called source_strings.txt and writes to a file called results.txt

 In addition to your programs, you must also submit a README file with clearly

delineated sections for the following.

 

 

0. Please write down the full names and netids of both your team members.

1. Are there known issues or functions that aren't working currently in your

   attached code? If so, explain. (note that you will get half credit for any reasonably sized bug that is fully explained in the readme)

3. What problems did you face developing code for this project? Around how long did you spend on this project (This helps me decide what I need to explain more clearly for the next projects)