Implementing a Versatile DNS Server in Python: Handling A, AAAA, CNAME, and TXT Records

CK 3788
Created at Mar 16, 2024 05:55:37

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Supporting AAAA records, which are used for IPv6 addresses, is a straightforward extension of the previous examples. The AAAA record type is essential for modern applications that operate over IPv6 networks. Here's how you can modify the existing Python DNS server example to handle AAAA records in addition to A, CNAME, and TXT records:

from socket import socket, AF_INET, SOCK_DGRAM
from dnslib import DNSRecord, RR, QTYPE, TXT

# Define DNS records (for demonstration purposes)
dns_records = {
    'example.com.': ('A', '192.168.1.100'),
    'ipv6.example.com.': ('AAAA', '2001:0db8:85a3:0000:0000:8a2e:0370:7334'),
    'sub.example.com.': ('A', '192.168.1.101'),
    'another.example.com.': ('A', '192.168.1.102'),
    'alias.example.com.': ('CNAME', 'example.com.'),
    'info.example.com.': ('TXT', 'This is a test TXT record'),
}

# Create UDP socket
sock = socket(AF_INET, SOCK_DGRAM)
sock.bind(('0.0.0.0', 53))  # Bind to port 53

# Handle DNS queries
while True:
    data, addr = sock.recvfrom(512)  # Buffer size is 512 bytes
    dns_request = DNSRecord.parse(data)

    # Prepare DNS response
    dns_response = DNSRecord(DNSRecord.HEADER.ID(dns_request.header.id))
    dns_response.add_question(dns_request.q.qname)

    qname = str(dns_request.q.qname)

    # Check if the query name exists in the records
    if qname in dns_records:
        record_type, value = dns_records[qname]
        if record_type == 'A':
            dns_response.add_answer(RR(qname, QTYPE.A, rdata=value, ttl=60))
        elif record_type == 'AAAA':
            dns_response.add_answer(RR(qname, QTYPE.AAAA, rdata=value, ttl=60))
        elif record_type == 'CNAME':
            dns_response.add_answer(RR(qname, QTYPE.CNAME, rdata=value, ttl=60))
            # Optionally, add the corresponding A or AAAA record for the CNAME
            if value in dns_records and (dns_records[value][0] == 'A' or dns_records[value][0] == 'AAAA'):
                dns_response.add_answer(RR(value, QTYPE[dns_records[value][0]], rdata=dns_records[value][1], ttl=60))
        elif record_type == 'TXT':
            dns_response.add_answer(RR(qname, QTYPE.TXT, rdata=TXT(value), ttl=60))

    # Send DNS response
    sock.sendto(dns_response.pack(), addr)

In this version, an example AAAA record for ipv6.example.com. with an IPv6 address (2001:0db8:85a3:0000:0000:8a2e:0370:7334) is added to the dns_records dictionary. This dictionary maps domain names to tuples that specify the record type ('A', 'AAAA', 'CNAME', 'TXT') and the record's value (IP address or text).

When constructing the DNS response, the code now checks for 'AAAA' record types alongside the other types and adds the corresponding RR object with QTYPE.AAAA and the IPv6 address as the rdata if a match is found.

This enhanced server is capable of responding to DNS queries for IPv4 (A), IPv6 (AAAA), canonical names (CNAME), and text records (TXT), covering a broader range of DNS record types.

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