如何用Python查找域名对应的CDN？解决CNAME查询无结果问题

First, let's clear up why your youtube.com CNAME query failed: Apex domains (like the root youtube.com, not subdomains such as www.youtube.com) can't have CNAME records due to DNS protocol rules. Instead, they use A/AAAA records to point directly to IP addresses owned by Google's CDN infrastructure. That's exactly why you're hitting the NoAnswer error.

Here are practical, actionable alternatives to identify the CDN when CNAME records aren't available:

1. Resolve A/AAAA Records & Check IP Ownership #

Most CDN providers control large blocks of registered IP addresses. You can resolve the domain's IPs, then look up which organization those IPs belong to to map back to the CDN.

Example Code: #

import dns.resolver
from ipwhois import IPWhois

def identify_cdn_via_ip(domain):
    # Fetch A records for the domain
    try:
        a_records = dns.resolver.query(domain, 'A')
        for ip in a_records:
            ip_str = str(ip)
            # Look up IP ownership details
            ip_whois = IPWhois(ip_str)
            rdap_results = ip_whois.lookup_rdap()
            org_name = rdap_results['network']['name']
            
            print(f"IP {ip_str} is registered to: {org_name}")
            # Map organization names to known CDNs
            if 'GOOGLE' in org_name.upper():
                return "Google CDN/YouTube CDN"
            # Add checks for other CDNs here (e.g., 'CLOUDFLARE' for Cloudflare)
    except dns.resolver.NoAnswer:
        print(f"No A records found for {domain}")
    return "Unknown CDN"

# Test with youtube.com
print(identify_cdn_via_ip('youtube.com'))

Running this will return "Google CDN/YouTube CDN" since all youtube.com IPs are registered to Google.

2. Inspect HTTP Response Headers #

Many CDNs add unique headers to HTTP responses. You can send a simple request and check headers like Server, X-Cache, or X-CDN for telltale signs.

Example Code: #

import requests

def identify_cdn_via_headers(domain):
    try:
        response = requests.get(f"https://{domain}", timeout=5)
        # Check common CDN-related headers
        server_header = response.headers.get('Server', '')
        x_cache_header = response.headers.get('X-Cache', '')
        
        if 'gws' in server_header.lower() or 'google' in x_cache_header.lower():
            return "Google CDN"
        # Add checks for other CDNs (e.g., 'cloudflare' in server_header for Cloudflare)
    except requests.exceptions.RequestException as e:
        print(f"Request failed: {str(e)}")
    return "Unknown CDN"

# Test with youtube.com
print(identify_cdn_via_headers('youtube.com'))

For YouTube, you'll typically see Server: gws (Google Web Server) in the response headers, confirming it uses Google's infrastructure.

3. Check DNS TXT/SPF Records (Less Reliable) #

Some CDNs leave traces in TXT or SPF records (often for domain verification), though this isn't a universal method.

Example Code: #

import dns.resolver

def check_cdn_in_txt_records(domain):
    try:
        txt_records = dns.resolver.query(domain, 'TXT')
        for record in txt_records:
            record_str = str(record)
            if 'google' in record_str.lower():
                return "Google-related infrastructure"
    except dns.resolver.NoAnswer:
        print(f"No TXT records found for {domain}")
    return "No CDN indicator found in TXT records"

# Test with youtube.com
print(check_cdn_in_txt_records('youtube.com'))

Quick Tips: #

• For apex domains like youtube.com, always start with A/AAAA records—CNAMEs are not allowed here by DNS standards.
• IP ownership lookup is more reliable than header checks, as some CDNs hide or customize headers.
• Combine multiple methods for higher accuracy (e.g., cross-reference IP ownership with header data).

内容的提问来源于stack exchange，提问作者Paul