Teamviewer is unable to connect to the servers because it is getting NXDOMAIN replies when trying to connect to router7.teamviewer.com (or any other routerX hostname).
The auhtoritative response to router7.teamviewer.com is ok and it is a CNAME routerpool7.rlb.teamviewer.com. But response to A query for routerpool7.rlb.teamviewer.com on authoritave DNS server 185.81.208.1 is NXDOMAIN
@185.81.208.1 routerpool7.rlb.teamviewer.com
; <<>> DiG 9.10.3-P4-Ubuntu <<>> @185.81.208.1 routerpool7.rlb.teamviewer.com
; (1 server found)
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NXDOMAIN, id: 45639
;; flags: qr aa rd; QUERY: 1, ANSWER: 0, AUTHORITY: 0, ADDITIONAL: 1
;; WARNING: recursion requested but not available
;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 4096
;; QUESTION SECTION:
;routerpool7.rlb.teamviewer.com. IN A
;; Query time: 186 msec
;; SERVER: 185.81.208.1#53(185.81.208.1)
;; WHEN: Tue Apr 28 08:21:23 CEST 2020
;; MSG SIZE rcvd: 5
This happens only in specific network. Could that be an issue on your DNS server or datacenter?
Besides that it seems that there is also an issue with DNSSEC according to dnsviz https://dnsviz.net/d/router7.teamviewer.com/Xqc93A/dnssec/
