QuestionPlease write your program in python. In this lab, you will… Please write your program in python.In this lab, you will implement a DNS client that can query an existing DNS server for domain name to IP address translation. We discussed in class the operations of DNS and types of messages (query and response) used by DNS protocol. Nslookup and dig are two tools that can be used to achieve the same translation using command line. However, in this programming assignment, you will manually handcraft DNS query messages, send them to known DNS servers, and process their response. You have been provided with specifics of DNS message format (which we also discussed in class) in the following description.Your DNS client has three big high-level pieces (in order of operations):DNS query: the client should read the hostname provided by a user and prepare a query message which adheres to DNS protocol specifications. Note that if you message does not adhere to the specifications, DNS server will not be able to identify/understand your query.Send query: the client should create a UDP socket connection to the server and send the DNS query message you prepared above.Receive and process DNS response: the client should receive a response from the DNS server. It should then process the response based on the format of DNS response message. It should extract the necessary information (IP address and more) and display it to the user on command line.We will now look at each of the three above pieces in details.DNS queryYour client should be able to read the hostname provided by a user. The hostname will be provided as a command line argument to your client program as follows$> my-dns-client An example of this would be – $> my-dns-client gmu.eduAlthough a typical DNS client can query multiple hostnames at the same time, we will restrict to only one hostname as an argument in this programming assignment.Once your client program reads the hostname, it should prepare a DNS query message. The general format of the DNS query and response message is provided in our book (Fig. 2.21). Specific bit-by-bit format of the query message can be found in the official DNS RFC document (https://tools.ietf.org/html/rfc1035#page-25). It is highly recommended that you go through the official RFC to clearly understand the role and purpose of each field before starting the code.The query and response messages have 5 sections shown in Fig. 1. Your query message will only first two sections. + Header + – – Question the questionfor the name server + – Answer RRsanswering the question +- … Show more… Show moreFig. 1: DNS message sectionsThe header contains the following fields (refer to Fig.2):Fig. 2: Fields of Header sectionWe have described only the important fields here. You should read the RFC and learn about the specifics of each field.ID: A 16 bit id that can uniquely identify a query message. Note that when you send multiple query messages, you will use this ID to match the responses to queries. The ID can be randomly generated by your client program.QR: 0 for query and 1 for response.OPCODE: We are only interested in standard query.RD: This bit is set if client wants the name server to recursively pursue the query. We will set this to 1.QDCOUNT: Since we are only sending one hostname query at a time, we will set this to 1.The question section has the following format (more details available from the RFC draft).Fig. 3: Fields of question sectionQNAME: it contains multiple labels – one for each section of a URL. For example, for gmu.edu, there should be two labels for gmu and edu. Each label consists of a length octet (3 for gmu), followed by ASCII code octets (67 for g, 6D for m, 75 for u). This is repeated for each label of the URL. The QNAME terminates with the zero length octet for the null label of the root. Note that this field may be an odd number of octets; no padding is used.QTYPE: Set to 1 because we are only interested in A type records. You can ignore NS, MX and CNAME type records for this assignment.Your client program can first calculate the above fields for both sections and then concatenate them. Note that the data type of each field can be different (binary, integer, string, hex, etc.), but they should all be converted to hexadecimal to form a complete message. Make sure to remove any unnecessary white spaces or new line characters which might be part of your strings.Send QueryOnce you have prepared a query message, your client program will establish a socket connection with a DNS server. As we discussed in the class, DNS uses UDP for transferring the message. Choose an appropriate port number for communication with the server. We will use Google’s public DNS server in the programming assignment. You can learn about public DNS server athttps://www.lifewire.com/free-and-public-dns-servers-2626062. The IP address of Google’s public DNS server is 8.8.8.8. You can use any other DNS server (for example, gmu’s DNS server) for testing, but your assignment will be graded only for 8.8.8.8 server.DNS query messages sent over UDP can be lost in the network. Your code should implement a timeout based retry where it waits for 5 seconds and if the server does not respond within that time, it resend the query message. If no response is received after 3 attempts, this should print out an error message about timeout.Receive and process responseAfter sending the DNS query to server, the server will reply back. Assuming your query is properly formatted and the server is able to understand your request, the response will follow standard DNS response message format. If your query message is not properly formatted, you might receive an error message in response or not receive any reply at all! A good starting point here is to receive whatever the server is sending back in a buffer and analyzing it.A response can have all five sections shown in Fig.1. First, let us assume that this is a standard response, in which case, it will have top three sections (header, question and answer).The header section will be similar to that of DNS query.ID will be the same as the query.QR will be set to 1 because it is a response.AA will depend on if the server is authority for the domain or not (most likely it is not, so AA is 0).RCODE: response code will be 0 if no errors, and >0 otherwise.As with the query format, make sure to go over the RFC specification to ensure each field is properly interpreted by your client.The question section will be exactly the same as the query message.The answer section will include one or more resource records (RRs). An RR has the following format:Fig. 3: Resource Record (RR) formatSome of the important fields are:NAME is the domain for which the IP address is resolved. It uses a compressed format which can be ignored in your processing.TYPE and CLASS are the same as query messages.TTL (Time To Live): specifies the time interval (in seconds) that the RR may be cached before considered outdated.RDATA is the resolved IP address.After your client program has parsed and processed the request, your client program should print tuple for every field of the response message. This would look something like: $> my-dns-client gmu.edu Preparing DNS query.. Contacting DNS server.. Sending DNS query.. DNS response received (attempt 1 of 3) Processing DNS response.. —————————————————————————- header.ID = header.QR = header.OPCODE = …. …. question.QNAME = question.QTYPE = question.QCLASS = …. …. answer.NAME = answer.TYPE = …. …. answer.RDATA = ## resolved IP address ## …. (include any authority or additional RRs received in the response also) —————————————————————————Computer ScienceEngineering & TechnologyPython Programming CS 455
