DNSprobe Wiki - IP
ASN Information
The ASN section identifies the network announcing an IP address on the internet.
An ASN indicates the network operator, routed prefix, and often the country associated with the BGP announcement.
This is useful for understanding which provider hosts an IP and whether it matches the expected service provider.
1. Overview
BGP lets autonomous systems announce the IP blocks they route. Each autonomous system has an ASN.
The ASN does not prove the final owner of a website, but it gives strong context about the infrastructure in use.
2. What DNSprobe checks
DNSprobe queries public routing data for the tested address.
- AS number associated with the IP.
- Announced IP prefix.
- Country and network organization name when available.
3. Interpreting results
Compare the returned ASN with the host, CDN, or provider you actually use.
- An expected ASN often confirms that DNS points to the right infrastructure.
- An unknown ASN may indicate an old host, proxy, or DNS routing mistake.
- The BGP country does not always match the exact physical server location.
4. Best practices
- Document allowed ASNs for critical domains.
- Check ASN after DNS or CDN migrations.
- Monitor unexpected prefix or operator changes.
- Cross-check with certificates, WHOIS, and provider data.
5. Manual tests
Query Team Cymru or a BGP service.
whois -h whois.cymru.com " -v 203.0.113.10"
whois 203.0.113.10ASN data changes with BGP announcements and can vary by source.