This project is an implementation of a DNS server in Python. The DNS server listens for DNS queries, processes them, and sends back responses. The project is being developed incrementally, with a focus on understanding the DNS protocol and building out the various features of a functioning DNS server.
- The server listens on
127.0.0.1at port2053and can receive DNS query packets over UDP.
-
The server constructs a DNS header according to DNS protocol specifications.
- Packet ID: Extracted from the incoming query.
- Flags: Properly set to indicate a standard query response, including handling the
QR,OPCODE,AA,TC,RD,RA,Z, andRCODEfields. - Counts:
QDCOUNT,ANCOUNT,NSCOUNT, andARCOUNTare appropriately set based on the response.
-
The question section from the query is extracted and included in the response.
- Name: Parsed from the query, currently handling uncompressed label sequences.
- Type: Always set to
1(A record) for this stage. - Class: Always set to
1(IN class).
- The server constructs the Answer section in DNS responses.
- Returns IP addresses for known domains based on a static domain-to-IP mapping.
- Uses pointer compression in the DNS response for efficient encoding.
- A Record Handling:
- Name: Encoded as a pointer to the domain name in the question section.
- Type: Set to
1(A record). - Class: Set to
1(IN class). - TTL: Set to
300seconds. - RDLENGTH: Set to
4bytes (length of IPv4 address). - RDATA: Encoded IPv4 address (e.g.,
8.8.8.8).
- If a domain is not found in the local mapping:
- The server forwards the query to an upstream DNS server (e.g., Google DNS at
8.8.8.8). - Handles the response from the upstream server and sends it back to the client.
- Sets appropriate
RCODEvalues based on the outcome:0(No Error) if the upstream server resolves the domain.2(Server Failure) if the upstream server does not respond.3(Name Error) if the domain does not exist.
- The server forwards the query to an upstream DNS server (e.g., Google DNS at
- Created a
domain_mappings.pyfile to store domain-to-IP mappings separately from the main server code.- Enhances code organization and maintainability.
- Example:
domain_ip_mapping = { 'example.com': '8.8.8.8', 'test.com': '8.8.4.4', 'helloworld.com': '1.1.1.1', 'random.org': '1.0.0.1' }
- Implemented detailed logging in
main.pyusing Python'sloggingmodule.- Logs incoming queries, responses sent, forwarding actions, and any errors encountered.
- Helps in debugging and monitoring server operations.
- Example log entries:
2024-09-18 13:58:35,000 - INFO - DNS server is starting... 2024-09-18 13:58:35,001 - INFO - DNS server is running on 127.0.0.1:2053 2024-09-18 13:58:36,002 - DEBUG - Received packet from ('127.0.0.1', 59070) 2024-09-18 13:58:36,003 - DEBUG - Received query for domain: google.com 2024-09-18 13:58:36,004 - INFO - Domain 'google.com' not found locally. Forwarding query. 2024-09-18 13:58:36,025 - DEBUG - Received response from upstream server for domain 'google.com'. 2024-09-18 13:58:36,026 - DEBUG - Sent response to ('127.0.0.1', 59070)
- Developed
tester.pyto rigorously test the DNS server's functionality.- Tests Included:
- Known Domains: Ensures that domains present in
domain_mappings.pyare resolved correctly. - Recursive Query Handling: Verifies that unknown domains are forwarded to the upstream DNS server and responses are correctly returned.
- Response Header Validation: Checks that the
ID,QR,OPCODE,AA,RD,RA, andRCODEfields are correctly set. - Answer Section Validation: Ensures that answer sections contain valid "A" records with correct IP addresses.
- Recursion Flags: Verifies that the server respects the
RD(Recursion Desired) flag when performing recursive queries.
- Known Domains: Ensures that domains present in
- Usage:
python tester.py
- Example Output:
Ran 6 tests in 2.018s OK
- Tests Included:
-
Implemented:
- Modified the
extract_domain_namefunction inmain.pyto handle compressed labels in the question section. - Ensures that domain names with compressed label sequences are correctly parsed and included in the response.
- Modified the
-
Next Steps:
- Thoroughly test the parsing of compressed labels using various DNS clients and test cases.
- Ensure that the response includes the uncompressed question section as required.
-
Respecting RD Flag from Client:
- Modify the server to check the client's
RD(Recursion Desired) flag. - Perform recursion only if the
RDflag is set. - If the
RDflag is not set, respond with an authoritative answer or appropriate error codes without performing recursion.
- Modify the server to check the client's
-
Support for Additional Record Types:
- Implement handling of
AAAA(IPv6),CNAME,MX, and other DNS record types. - Extend the server to support these records in both question and answer sections.
- Implement handling of
-
Dynamic Domain Loading:
- Implement dynamic reloading of
domain_mappings.pywithout restarting the server. - Allow real-time updates to DNS records for better flexibility and maintenance.
- Implement dynamic reloading of
-
Improved Error Handling:
- Enhance exception handling to gracefully manage malformed queries, network issues, and unexpected upstream responses.
- Implement comprehensive
RCODEresponses based on different error scenarios.
-
Caching Mechanism:
- Add a caching system to store responses from upstream servers.
- Utilize TTL values to determine cache expiration, reducing latency and u 8000 pstream DNS queries.
-
Security Enhancements:
- Implement DNSSEC validation to protect against cache poisoning and other DNS-based attacks.
- Introduce rate limiting and access control lists (ACLs) to prevent abuse and Denial of Service (DoS) attacks.
-
Concurrency and Performance Optimization:
- Enhance the server to handle multiple simultaneous queries using threading or asynchronous I/O.
- Optimize response times and resource utilization for better scalability.
-
Logging and Monitoring Improvements:
- Expand logging to include more granular details such as cache hits/misses, query sources, and response times.
- Integrate monitoring tools to track server performance and detect anomalies.
-
Zone Transfers (for Authoritative Servers):
- Implement AXFR/IXFR support to enable zone transfers between primary and secondary DNS servers.
- Ensure secure and efficient synchronization of DNS records across multiple servers.
-
Server Startup:
- The server initializes a UDP socket and binds to
127.0.0.1:2053. - Logging is configured to provide detailed output for monitoring and debugging.
- The server initializes a UDP socket and binds to
-
Query Processing:
- The server waits for incoming DNS query packets.
- Upon receiving a query:
- Extracts the domain name from the question section, handling both uncompressed and compressed labels.
- Logs the received domain name and relevant query flags.
-
Response Construction:
- Known Domains:
- If the domain exists in
domain_mappings.py, the server constructs a DNS response including the Answer section with the corresponding "A" record. - Sets
ANCOUNTto1and populates the Answer section with the IP address.
- If the domain exists in
- Unknown Domains:
- For domains not found locally, the server forwards the query to an upstream DNS server (e.g., Google DNS at
8.8.8.8). - Handles the upstream response and sends it back to the client.
- Sets appropriate
RCODEvalues based on the outcome.
- For domains not found locally, the server forwards the query to an upstream DNS server (e.g., Google DNS at
- Known Domains:
-
Logging:
- Throughout the process, the server logs important events, including received queries, forwarding actions, responses sent, and any errors encountered.
- Logs include timestamps, severity levels, and descriptive messages to aid in monitoring and debugging.
- Python 3.x installed on your system.
- Start the Server:
python main.py
- The server will start and listen on
127.0.0.1:2053. - Logs will be printed to the console, detailing incoming queries and responses.
- The server will start and listen on
- Ensure the server is not already running separately, as the tester will start it internally.
python tester.py- The tester script will perform several tests and output the results.
- It tests known domains, recursive query handling, response integrity, and more.
- You can use the
digcommand to test the server manually.
For a Known Domain (e.g., example.com):
dig @127.0.0.1 -p 2053 example.comExpected Output:
- The server should return the IP address specified in
domain_mappings.pyforexample.com.
For an Unknown Domain (e.g., google.com):
dig @127.0.0.1 -p 2053 google.comExpected Output:
- The server should resolve the domain via the upstream DNS server and return the appropriate IP address.
Testing Without Recursion:
dig @127.0.0.1 -p 2053 google.com +norecurse- Note: Currently, the server does not respect the
RDflag from the client and will perform recursion regardless.
main.py: The main DNS server implementation.domain_mappings.py: Contains the domain-to-IP mappings.tester.py: Script for testing the DNS server.README.md: Project documentation and usage instructions.
Server Console Logs:
2024-09-18 13:58:35,000 - INFO - DNS server is starting...
2024-09-18 13:58:35,001 - INFO - DNS server is running on 127.0.0.1:2053
2024-09-18 13:58:36,002 - DEBUG - Received packet from ('127.0.0.1', 59070)
2024-09-18 13:58:36,003 - DEBUG - Received query for domain: google.com
2024-09-18 13:58:36,004 - INFO - Domain 'google.com' not found locally. Forwarding query.
2024-09-18 13:58:36,025 - DEBUG - Received response from upstream server for domain 'google.com'.
2024-09-18 13:58:36,026 - DEBUG - Sent response to ('127.0.0.1', 59070)
Tester Script Output:
Ran 6 tests in 2.018s
OK
-
Handling Compressed Labels:
- Currently, the server can parse compressed labels in the question section, but thorough testing is ongoing to ensure robustness.
-
Respecting RD Flag:
- The server does not currently respect the client's
RD(Recursion Desired) flag and will perform recursion even if the client does not request it.
- The server does not currently respect the client's
-
Record Types Supported:
- The server currently handles only
Arecords (IPv4 addresses). Support for other record types likeAAAA,CNAME,MX, etc., is not yet implemented.
- The server currently handles only
-
Concurrency:
- The server handles queries sequentially. Implementing concurrency (e.g., threading or asynchronous I/O) is planned for future stages to improve performance.
-
Security Features:
- Basic security measures like rate limiting, access control, and DNSSEC validation are not yet implemented.
-
Respecting RD Flag from Client:
- Modify the server to check the client's
RD(Recursion Desired) flag. - Perform recursion only if the
RDflag is set. - If the
RDflag is not set, respond with an authoritative answer or appropriate error codes without performing recursion.
- Modify the server to check the client's
-
Support for Additional Record Types:
- Implement handling of
AAAA(IPv6),CNAME,MX, and other DNS record types. - Extend the server to support these records in both question and answer sections.
- Implement handling of
-
Dynamic Domain Loading:
- Implement dynamic reloading of
domain_mappings.pywithout restarting the server. - Allow real-time updates to DNS records for better flexibility and maintenance.
- Implement dynamic reloading of
-
Improved Error Handling:
- Enhance exception handling to gracefully manage malformed queries, network issues, and unexpected upstream responses.
- Implement comprehensive
RCODEresponses based on different error scenarios.
-
Caching Mechanism:
- Add a caching system to store responses from upstream servers.
- Utilize TTL values to determine cache expiration, reducing latency and upstream DNS queries.
-
Security Enhancements:
- Implement DNSSEC validation to protect against cache poisoning and other DNS-based attacks.
- Introduce rate limiting and access control lists (ACLs) to prevent abuse and Denial of Service (DoS) attacks.
-
Concurrency and Performance Optimization:
- Enhance the server to handle multiple simultaneous queries using threading or asynchronous I/O.
- Optimize response times and resource utilization for better scalability.
-
Logging and Monitoring Improvements:
- Expand logging to include more granular details such as cache hits/misses, query sources, and response times.
- Integrate monitoring tools to track server performance and detect anomalies.
-
Zone Transfers (for Authoritative Servers):
- Implement AXFR/IXFR support to enable zone transfers between primary and secondary DNS servers.
- Ensure secure and efficient synchronization of DNS records across multiple servers.
- The tester script (
tester.py) was developed with assistance from OpenAI GPT to ensure comprehensive testing of the DNS server.
Feel free to explore, modify, and extend this project. Contributions and feedback are welcome!
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Fork the Repository: Create your own fork of the project.
-
Clone the Fork:
git clone https://github.com/your-username/dns-server-python.git
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Create a New Branch:
git checkout -b feature/your-feature-name
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Make Changes: Implement your feature or bug fix.
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Commit Changes:
git add . git commit -m "Describe your changes"
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Push to Your Fork:
git push origin feature/your-feature-name
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Create a Pull Request: Submit a pull request to the original repository.
This project is open-source and available under the MIT License.
If you have any questions or need assistance, feel free to reach out!
Note: In the future, we plan to respect the client's RD flag to fully comply with DNS standards.