Domain name existence via “dig”

问题

Would it be possible to check a domain name its existence by checking the output of "dig"? Inside the bind sources I found these constants:

0 DNS_R_NOEROR
1 DNS_R_FORMERR
2 DNS_R_SERVFAIL
3 DNS_R_NXDOMAIN
4 DNS_R_NOTIMP
5 DNS_R_REFUSED
6 DNS_R_YXDOMAIN
7 DNS_R_YXRRSET
8 DNS_R_NXRRSET
9 DNS_R_NOTAUTH
10 DNS_R_NOTZONE
16 DNS_R_BADVERS

<RCODE 11>     # 11 has no macro
<RCODE 12>     # 12 has no macro
<RCODE 13>     # 13 has no macro
<RCODE 14>     # 14 has no macro
<RCODE 15>     # 15 has no macro

In my opinion NOERROR & SERVFAIL means the hostname exists (although it doesn't mean an ip is linked to it). NXDOMAIN would mean it absolutely not exists.

I prefer not to use whois because it is quite slow. dig is much faster as I just need to be certain that the hostname doesn't exist yet.

Could someone shine their light on my assumptions and the other macros?

Thanks

回答1:

Well, in some cases it might work, but in most cases you will see incorrect results- some domains are registered but do not have a record in the TLD name server. And some domains have a record configured but are not registered as some registries have wildcard domains configured:

$ dig asdfasdfasdfxvyxv123.de.com A +short 
91.213.214.122

$ whois -h whois.centralnic.com asdfasdfasdfxvyxv123.de.com
DOMAIN NOT FOUND

whois indeed is slow - speak to a/your domain provider, most registries offer faster methods to check if a domain is registered or not (i.e. EPP protocol)

回答2:

No, you can't. At least, Dig can tell you if the domain has a nameserver record, but even if the response is negative, it doesn't mean the domain is available.

The only way is to perform a WHOIS query.

回答3:

Just ask for the SOA records of the domain :

$ dig activcloud.eu +short soa
dns112.ovh.net. tech.ovh.net. 2018091203 86400 3600 3600000 300

while

$ dig lmksjdflksd.eu +short soa

returns nothing

来源：https://stackoverflow.com/questions/4704368/domain-name-existence-via-dig

标签

dns

whois

dig