Hello. I have problems with name resolution thar are related to military invasion of russian army into Ukraine. Either some internet providers started to block ALL .ru / .su domains or this is a domain name cache issue at the side of public DNS servers, maybe related to hacker attacks started from both warring countries. I will not explain, just look at this
The domain that does not exist:
[email protected]:/# nslookup xxxxxxxxx.ru 1.1.1.1
Server: 1.1.1.1
Address: 1.1.1.1#53
** server can't find xxxxxxxxx.ru: SERVFAIL
[email protected]:/# nslookup xxxxxxxxx.zu 1.1.1.1
Server: 1.1.1.1
Address: 1.1.1.1#53
** server can't find xxxxxxxxx.zu: NXDOMAIN
[email protected]:/# nslookup xxxxxxxxx.com 1.1.1.1
Server: 1.1.1.1
Address: 1.1.1.1#53
** server can't find xxxxxxxxx.com: NXDOMAIN
[email protected]:/# nslookup xxxxxxxxx.com 8.8.8.8
Server: 8.8.8.8
Address: 8.8.8.8#53
** server can't find xxxxxxxxx.com: NXDOMAIN
[email protected]:/# nslookup xxxxxxxxx.zu 8.8.8.8
Server: 8.8.8.8
Address: 8.8.8.8#53
** server can't find xxxxxxxxx.zu: NXDOMAIN
[email protected]:/# nslookup xxxxxxxxx.ru 8.8.8.8
Server: 8.8.8.8
Address: 8.8.8.8#53
** server can't find xxxxxxxxx.ru: SERVFAIL
The domain that exists:
[email protected]:/# nslookup webhost1.ru 8.8.8.8
Server: 8.8.8.8
Address: 8.8.8.8#53
** server can't find webhost1.ru: SERVFAIL
[email protected]:/# nslookup webhost1.com 8.8.8.8
Server: 8.8.8.8
Address: 8.8.8.8#53
** server can't find webhost1.com: SERVFAIL
[email protected]:/# nslookup webhost1.ru 1.1.1.1
Server: 1.1.1.1
Address: 1.1.1.1#53
** server can't find webhost1.ru: SERVFAIL
[email protected]:/# nslookup webhost1.com 1.1.1.1
Server: 1.1.1.1
Address: 1.1.1.1#53
Non-authoritative answer:
Name: webhost1.com
Address: 91.236.136.40
Name: webhost1.com
Address: 91.236.136.5
Name: webhost1.com
Address: 91.236.136.4
I think in first case all must return NXDOMAIN, not SERVFAIL. Also some domains lookups sometimes may return error few times and since N-th try they will return correct IP.
How it could happen?