Multistage DNS Resolver System

Implemented a 2 stage DNS resolving system as shown:

Request Message Format:

Request Type	Message

• Type 1: Message field contains Domain Name and requests for corresponding IP address.
• Type 2: Message field contains IP address and request for the corresponding Domain Name.

Response Message Format:

Response Type	Message

• Type 3: Message field contains Domain Name/IP address.
• Type 4: Message field contains error message “Entry not found in the database”.

Commands to create executables:

gcc mainserver.c -o server.o
gcc -pthread proxy.c -o proxy.o
gcc client.c -o client.o

-pthread is used for POSIX semaphores/shared memory for concurrency.

Commands to run client,proxy and server:

./server.o <DNS_Server_Port>
./proxy.o <Proxy_Server_Port> <DNS_Server_IP> <DNS_Server_Port>
./client.o <Proxy_Server_IP> <Proxy_Server_Port>

The above commands must be run in the same order since the client requires proxy running and the proxy requires DNS server running. Example commands:

./server.o 8124
./proxy.o 8075 127.0.0.1 8124
./client.o 127.0.0.1 8075

Notes

• Each message transferred has a maximum size of MAXLINE = 100 bytes.
• The first byte of every message is the request/response type followed by message
• All hostname/ip mappings must be stored in "data.txt"
• Each line in "data.txt" must contain hostname and ip separated by only one space
• No extra new line should exist at the end of "data.txt"