The goal of this project is to implement a simplified DNS system consisting of a client program and two server programs: RS (a simplified root DNS server) and TS (a simplified top-level DNS server). In project 0 (your first HW) , you have already seen a client-server program with one socket each in the client and the server. In this project, you will extend that implementation to have two sockets in the client program. One socket will be used to communicate with RS and the other with TS.
The RS and TS programs each maintain a DNS_table consisting of three fields:
- Hostname
- IP address
- Flag (A or NS)
You need to choose the appropriate data structure to store the values for each entry. The client always connects first to RS, sending the queried hostname as a string. The RS program does a look up in its DNS_table, and if there is a match, sends the entry as a string
Hostname IPaddress A
If there is no match, RS sends the string TSHostname - NS where TShostname is the name of the machine on which the TS program is running.
If the client receives a string with "A" field, it outputs the received string as is. On the other hand, if the client receives a string with "NS" field, it uses the TSHostname part of the received string to determine the IP address of the machine running the TS program and connects to the TS program using a second socket. The client then sends the queried hostname as a string to TS. The TS program looks up the hostname in its DNS_table, and if there is a match, sends the entry as a string
Hostname IP address A to the client. Otherwise, it sends an error string
Hostname - Error:HOST NOT FOUND
In the TS outputs above, Hostname is the queried hostname. The client outputs the string received from TS as is.
Note that all DNS lookups are case-insensitive. If there is a hit in the local
DNS table, the server programs must respond with the version of the string that
is in their local DNS table.
