Server Fault is a question and answer site for system and network administrators. Join them; it only takes a minute:

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

I just signed up Cloudfare and they showed me a list of my subdomains by scanning my domain.

How do they do this? What technology is used to scan all subdomains related to a root domain?

share|improve this question
Can you explain that a little bit further? It is possible that they just did a zone transfer (depending on your DNS settings) – MichelZ Apr 16 '14 at 17:34
Have a look here – MichelZ Apr 16 '14 at 17:36
My setup does not allow axfr zone transfer – Isabella Wilcox Apr 16 '14 at 17:39
To pick a nit: You do not have a root domain. There is only one root domain and it is at the root (of all places). What you have is most likely a second or third level domain name. – yoonix Apr 16 '14 at 17:40
up vote 3 down vote accepted

They flood your DNS server with requests for "common" entries. It definitely does not get them all, just tried on one of my domains with "weird" subdomains and it only caught about half of them.

share|improve this answer

One possibility is to just google for the domain name and see what subdomains come up.


share|improve this answer

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.