Making Reverse DNS Lookups in Python with aiohttp

Mar 3, 2024 ยท 2 min read

When building network applications in Python, you may need to perform reverse DNS lookups to convert an IP address to a hostname. The aiohttp library provides an easy way to make asynchronous reverse DNS lookups.

A reverse DNS lookup takes an IP address like and returns the hostname associated with it, in this case

Here is how to make a reverse DNS lookup with aiohttp:

import aiohttp

async with aiohttp.ClientSession() as session:
    async with session.get(f'{ip}&type=PTR') as resp:
        data = await resp.json()
        hostname = data['Answer'][0]['data']

The key things to note:

  • We use an aiohttp client session for asynchronous HTTP requests
  • The Google DNS API endpoint can return PTR records for reverse DNS lookups
  • We await the JSON response and extract the hostname from the Answer data
  • Some tips when doing reverse DNS with aiohttp:

  • Handle errors - the hostname lookup could fail or return multiple names
  • Cache results - reverse DNS usually doesn't change often for an IP
  • Rate limit requests - don't overload DNS servers with too many queries
  • You may also want to validate hostnames after the reverse lookup to check if they resolve back to the original IP.

    Here is an example wrapper function that does a reverse lookup along with forward validation:

    async def reverse_dns(ip):
        async with aiohttp.ClientSession() as session:
                resp = await session.get(f'{ip}&type=PTR')
                data = await resp.json()
                hostname = data['Answer'][0]['data']
                return None
            forward_resp = await session.get(f'{hostname}&type=A')
            forward_data = await forward_resp.json()
            if ip not in [answer['data'] for answer in forward_data['Answer']]:
                return None
            return hostname  

    This provides robust reverse DNS lookups from Python with aiohttp and handles some of the potential pitfalls like invalid responses.

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