DNS Sinkhole Server

A DNS sinkhole server that iteratively resolves any request for domains that not included in a given list of domains to block

What is a typical flow of the server?

The server is listening on port 5300 🠊

The server receives a DNS request from a client 🠊

The server checks if the domain name that needs to be resolved is specified in the blocklist file. If yes, return an error response 🠊

The server sends the request to a random root server 🠊

The server received a response from the random root server 🠊

Until there is no answer, the server sends a request to the next DNS server. The name of the next DNS server is extracted from the authority section of the last response 🠊

Send the final response to the client

How to use?

1. Download the project.

2. Build the project using the follow command:

   $ javac -d out/ -Xlint src/il/ac/idc/cs/sinkhole/*.java

3. Run the server using the following command:

   $ java -cp out il.ac.idc.cs.sinkhole.SinkholeServer

   or if you want that the server will use a block list file called blocklist.txt:

   $ java -cp out il.ac.idc.cs.sinkhole.SinkholeServer blocklist.txt

Additional info:

• Supports reading compressed data according to RFC 1035 section 4.1.4
• Supports a valid DNS query of type A only
• Implements a query timeout of 5 seconds, so for example if a root server doesn’t respond, the server will cancel the query and advance to the next one
• The block list file is a text file containing one valid domain name to block per line. You can view an example file in the root directory of the project
• The project was tested with Java 11