Error in updating UCS 4.4

Administrator@DC:~$ sudo apt-get update
Err:1 https://updates.software-univention.de/4.4/maintained 4.4-5/all/ InRelease
Could not resolve host: updates.software-univention.de
Err:2 https://updates.software-univention.de/4.4/maintained 4.4-5/amd64/ InRelease
Could not resolve host: updates.software-univention.de
Err:3 https://updates.software-univention.de/4.4/maintained/component 4.4-4-errata/all/ InRelease
Could not resolve host: updates.software-univention.de
Err:4 https://updates.software-univention.de/4.4/maintained/component 4.4-4-errata/amd64/ InRelease
Could not resolve host: updates.software-univention.de
Err:5 https://updates.software-univention.de/4.0/maintained 4.0-0/all/ InRelease
Could not resolve host: updates.software-univention.de
Err:6 https://updates.software-univention.de/4.0/maintained 4.0-0/amd64/ InRelease
Could not resolve host: updates.software-univention.de
Err:7 https://updates.software-univention.de/4.0/maintained 4.0-1/all/ InRelease
Could not resolve host: updates.software-univention.de
Err:8 https://updates.software-univention.de/4.0/maintained 4.0-1/amd64/ InRelease
Could not resolve host: updates.software-univention.de
Err:9 https://updates.software-univention.de/4.0/maintained 4.0-2/all/ InRelease
Could not resolve host: updates.software-univention.de
Err:10 https://updates.software-univention.de/4.0/maintained 4.0-2/amd64/ InRelease
Could not resolve host: updates.software-univention.de
Err:11 https://updates.software-univention.de/4.0/maintained 4.0-3/all/ InRelease
Could not resolve host: updates.software-univention.de
Err:12 https://updates.software-univention.de/4.0/maintained 4.0-3/amd64/ InRelease
Could not resolve host: updates.software-univention.de
Err:13 https://updates.software-univention.de/4.0/maintained 4.0-4/all/ InRelease
Could not resolve host: updates.software-univention.de
Err:14 https://updates.software-univention.de/4.0/maintained 4.0-4/amd64/ InRelease
Could not resolve host: updates.software-univention.de
Err:15 https://updates.software-univention.de/4.0/maintained 4.0-5/all/ InRelease
Could not resolve host: updates.software-univention.de
Err:16 https://updates.software-univention.de/4.0/maintained 4.0-5/amd64/ InRelease
Could not resolve host: updates.software-univention.de
Err:17 https://updates.software-univention.de/4.1/maintained 4.1-0/all/ InRelease
Could not resolve host: updates.software-univention.de
Err:18 https://updates.software-univention.de/4.1/maintained 4.1-0/amd64/ InRelease
Could not resolve host: updates.software-univention.de
Err:19 https://updates.software-univention.de/4.1/maintained 4.1-1/all/ InRelease
Could not resolve host: updates.software-univention.de
Err:20 https://updates.software-univention.de/4.1/maintained 4.1-1/amd64/ InRelease
Could not resolve host: updates.software-univention.de
Err:21 https://updates.software-univention.de/4.1/maintained 4.1-2/all/ InRelease
Could not resolve host: updates.software-univention.de
Err:22 https://updates.software-univention.de/4.1/maintained 4.1-2/amd64/ InRelease
Could not resolve host: updates.software-univention.de
Err:23 https://updates.software-univention.de/4.1/maintained 4.1-3/all/ InRelease
Could not resolve host: updates.software-univention.de
Err:24 https://updates.software-univention.de/4.1/maintained 4.1-3/amd64/ InRelease
Could not resolve host: updates.software-univention.de
Err:25 https://updates.software-univention.de/4.1/maintained 4.1-4/all/ InRelease
Could not resolve host: updates.software-univention.de
Err:26 https://updates.software-univention.de/4.1/maintained 4.1-4/amd64/ InRelease
Could not resolve host: updates.software-univention.de
Err:27 https://updates.software-univention.de/4.1/maintained 4.1-5/all/ InRelease
Could not resolve host: updates.software-univention.de
Err:28 https://updates.software-univention.de/4.1/maintained 4.1-5/amd64/ InRelease
Could not resolve host: updates.software-univention.de
Err:29 https://updates.software-univention.de/4.2/maintained 4.2-0/all/ InRelease
Could not resolve host: updates.software-univention.de
Err:30 https://updates.software-univention.de/4.2/maintained 4.2-0/amd64/ InRelease
Could not resolve host: updates.software-univention.de
Err:31 https://updates.software-univention.de/4.2/maintained 4.2-1/all/ InRelease
Could not resolve host: updates.software-univention.de
Err:32 https://updates.software-univention.de/4.2/maintained 4.2-1/amd64/ InRelease
Could not resolve host: updates.software-univention.de
Err:33 https://updates.software-univention.de/4.2/maintained 4.2-2/all/ InRelease
Could not resolve host: updates.software-univention.de
Err:34 https://updates.software-univention.de/4.2/maintained 4.2-2/amd64/ InRelease
Could not resolve host: updates.software-univention.de
Err:35 https://updates.software-univention.de/4.2/maintained 4.2-3/all/ InRelease
Could not resolve host: updates.software-univention.de
Err:36 https://updates.software-univention.de/4.2/maintained 4.2-3/amd64/ InRelease
Could not resolve host: updates.software-univention.de
Err:37 https://updates.software-univention.de/4.2/maintained 4.2-4/all/ InRelease
Could not resolve host: updates.software-univention.de
Err:38 https://updates.software-univention.de/4.2/maintained 4.2-4/amd64/ InRelease
Could not resolve host: updates.software-univention.de
Err:39 https://updates.software-univention.de/4.2/maintained 4.2-5/all/ InRelease
Could not resolve host: updates.software-univention.de
Err:40 https://updates.software-univention.de/4.2/maintained 4.2-5/amd64/ InRelease
Could not resolve host: updates.software-univention.de
Err:41 https://updates.software-univention.de/4.3/maintained 4.3-0/all/ InRelease
Could not resolve host: updates.software-univention.de
Err:42 https://updates.software-univention.de/4.3/maintained 4.3-0/amd64/ InRelease
Could not resolve host: updates.software-univention.de
Err:43 https://updates.software-univention.de/4.3/maintained 4.3-1/all/ InRelease
Could not resolve host: updates.software-univention.de
Err:44 https://updates.software-univention.de/4.3/maintained 4.3-1/amd64/ InRelease
Could not resolve host: updates.software-univention.de
Err:45 https://updates.software-univention.de/4.3/maintained 4.3-2/all/ InRelease
Could not resolve host: updates.software-univention.de
Err:46 https://updates.software-univention.de/4.3/maintained 4.3-2/amd64/ InRelease
Could not resolve host: updates.software-univention.de
Err:47 https://updates.software-univention.de/4.3/maintained 4.3-3/all/ InRelease
Could not resolve host: updates.software-univention.de
Err:48 https://updates.software-univention.de/4.3/maintained 4.3-3/amd64/ InRelease
Could not resolve host: updates.software-univention.de
Err:49 https://updates.software-univention.de/4.3/maintained 4.3-4/all/ InRelease
Could not resolve host: updates.software-univention.de
Err:50 https://updates.software-univention.de/4.3/maintained 4.3-4/amd64/ InRelease
Could not resolve host: updates.software-univention.de
Err:51 https://updates.software-univention.de/4.3/maintained 4.3-5/all/ InRelease
Could not resolve host: updates.software-univention.de
Err:52 https://updates.software-univention.de/4.3/maintained 4.3-5/amd64/ InRelease
Could not resolve host: updates.software-univention.de
Err:53 https://updates.software-univention.de/4.4/maintained 4.4-0/all/ InRelease
Could not resolve host: updates.software-univention.de
Err:54 https://updates.software-univention.de/4.4/maintained 4.4-0/amd64/ InRelease
Could not resolve host: updates.software-univention.de
Err:55 https://updates.software-univention.de/4.4/maintained 4.4-1/all/ InRelease
Could not resolve host: updates.software-univention.de
Err:56 https://updates.software-univention.de/4.4/maintained 4.4-1/amd64/ InRelease
Could not resolve host: updates.software-univention.de
Err:57 https://updates.software-univention.de/4.4/maintained 4.4-2/all/ InRelease
Could not resolve host: updates.software-univention.de
Err:58 https://updates.software-univention.de/4.4/maintained 4.4-2/amd64/ InRelease
Could not resolve host: updates.software-univention.de
Err:59 https://updates.software-univention.de/4.4/maintained 4.4-3/all/ InRelease
Could not resolve host: updates.software-univention.de
Err:60 https://updates.software-univention.de/4.4/maintained 4.4-3/amd64/ InRelease
Could not resolve host: updates.software-univention.de
Err:61 https://updates.software-univention.de/4.4/maintained 4.4-4/all/ InRelease
Could not resolve host: updates.software-univention.de
Err:62 https://updates.software-univention.de/4.4/maintained 4.4-4/amd64/ InRelease
Could not resolve host: updates.software-univention.de
Reading package lists… Done
W: Failed to fetch https://updates.software-univention.de/4.4/maintained/4.4-5/all/InRelease Could not resolve host: updates.software-univention.de
W: Failed to fetch https://updates.software-univention.de/4.4/maintained/4.4-5/amd64/InRelease Could not resolve host: updates.software-univention.de
W: Failed to fetch https://updates.software-univention.de/4.4/maintained/component/4.4-4-errata/all/InRelease Could not resolve host: updates.software-univention.de
W: Failed to fetch https://updates.software-univention.de/4.4/maintained/component/4.4-4-errata/amd64/InRelease Could not resolve host: updates.software-univention.de
W: Failed to fetch https://updates.software-univention.de/4.0/maintained/4.0-0/all/InRelease Could not resolve host: updates.software-univention.de
W: Failed to fetch https://updates.software-univention.de/4.0/maintained/4.0-0/amd64/InRelease Could not resolve host: updates.software-univention.de
W: Failed to fetch https://updates.software-univention.de/4.0/maintained/4.0-1/all/InRelease Could not resolve host: updates.software-univention.de
W: Failed to fetch https://updates.software-univention.de/4.0/maintained/4.0-1/amd64/InRelease Could not resolve host: updates.software-univention.de
W: Failed to fetch https://updates.software-univention.de/4.0/maintained/4.0-2/all/InRelease Could not resolve host: updates.software-univention.de
W: Failed to fetch https://updates.software-univention.de/4.0/maintained/4.0-2/amd64/InRelease Could not resolve host: updates.software-univention.de
W: Failed to fetch https://updates.software-univention.de/4.0/maintained/4.0-3/all/InRelease Could not resolve host: updates.software-univention.de
W: Failed to fetch https://updates.software-univention.de/4.0/maintained/4.0-3/amd64/InRelease Could not resolve host: updates.software-univention.de
W: Failed to fetch https://updates.software-univention.de/4.0/maintained/4.0-4/all/InRelease Could not resolve host: updates.software-univention.de
W: Failed to fetch https://updates.software-univention.de/4.0/maintained/4.0-4/amd64/InRelease Could not resolve host: updates.software-univention.de
W: Failed to fetch https://updates.software-univention.de/4.0/maintained/4.0-5/all/InRelease Could not resolve host: updates.software-univention.de
W: Failed to fetch https://updates.software-univention.de/4.0/maintained/4.0-5/amd64/InRelease Could not resolve host: updates.software-univention.de
W: Failed to fetch https://updates.software-univention.de/4.1/maintained/4.1-0/all/InRelease Could not resolve host: updates.software-univention.de
W: Failed to fetch https://updates.software-univention.de/4.1/maintained/4.1-0/amd64/InRelease Could not resolve host: updates.software-univention.de
W: Failed to fetch https://updates.software-univention.de/4.1/maintained/4.1-1/all/InRelease Could not resolve host: updates.software-univention.de
W: Failed to fetch https://updates.software-univention.de/4.1/maintained/4.1-1/amd64/InRelease Could not resolve host: updates.software-univention.de
W: Failed to fetch https://updates.software-univention.de/4.1/maintained/4.1-2/all/InRelease Could not resolve host: updates.software-univention.de
W: Failed to fetch https://updates.software-univention.de/4.1/maintained/4.1-2/amd64/InRelease Could not resolve host: updates.software-univention.de
W: Failed to fetch https://updates.software-univention.de/4.1/maintained/4.1-3/all/InRelease Could not resolve host: updates.software-univention.de
W: Failed to fetch https://updates.software-univention.de/4.1/maintained/4.1-3/amd64/InRelease Could not resolve host: updates.software-univention.de
W: Failed to fetch https://updates.software-univention.de/4.1/maintained/4.1-4/all/InRelease Could not resolve host: updates.software-univention.de
W: Failed to fetch https://updates.software-univention.de/4.1/maintained/4.1-4/amd64/InRelease Could not resolve host: updates.software-univention.de
W: Failed to fetch https://updates.software-univention.de/4.1/maintained/4.1-5/all/InRelease Could not resolve host: updates.software-univention.de
W: Failed to fetch https://updates.software-univention.de/4.1/maintained/4.1-5/amd64/InRelease Could not resolve host: updates.software-univention.de
W: Failed to fetch https://updates.software-univention.de/4.2/maintained/4.2-0/all/InRelease Could not resolve host: updates.software-univention.de
W: Failed to fetch https://updates.software-univention.de/4.2/maintained/4.2-0/amd64/InRelease Could not resolve host: updates.software-univention.de
W: Failed to fetch https://updates.software-univention.de/4.2/maintained/4.2-1/all/InRelease Could not resolve host: updates.software-univention.de
W: Failed to fetch https://updates.software-univention.de/4.2/maintained/4.2-1/amd64/InRelease Could not resolve host: updates.software-univention.de
W: Failed to fetch https://updates.software-univention.de/4.2/maintained/4.2-2/all/InRelease Could not resolve host: updates.software-univention.de
W: Failed to fetch https://updates.software-univention.de/4.2/maintained/4.2-2/amd64/InRelease Could not resolve host: updates.software-univention.de
W: Failed to fetch https://updates.software-univention.de/4.2/maintained/4.2-3/all/InRelease Could not resolve host: updates.software-univention.de
W: Failed to fetch https://updates.software-univention.de/4.2/maintained/4.2-3/amd64/InRelease Could not resolve host: updates.software-univention.de
W: Failed to fetch https://updates.software-univention.de/4.2/maintained/4.2-4/all/InRelease Could not resolve host: updates.software-univention.de
W: Failed to fetch https://updates.software-univention.de/4.2/maintained/4.2-4/amd64/InRelease Could not resolve host: updates.software-univention.de
W: Failed to fetch https://updates.software-univention.de/4.2/maintained/4.2-5/all/InRelease Could not resolve host: updates.software-univention.de
W: Failed to fetch https://updates.software-univention.de/4.2/maintained/4.2-5/amd64/InRelease Could not resolve host: updates.software-univention.de
W: Failed to fetch https://updates.software-univention.de/4.3/maintained/4.3-0/all/InRelease Could not resolve host: updates.software-univention.de
W: Failed to fetch https://updates.software-univention.de/4.3/maintained/4.3-0/amd64/InRelease Could not resolve host: updates.software-univention.de
W: Failed to fetch https://updates.software-univention.de/4.3/maintained/4.3-1/all/InRelease Could not resolve host: updates.software-univention.de
W: Failed to fetch https://updates.software-univention.de/4.3/maintained/4.3-1/amd64/InRelease Could not resolve host: updates.software-univention.de
W: Failed to fetch https://updates.software-univention.de/4.3/maintained/4.3-2/all/InRelease Could not resolve host: updates.software-univention.de
W: Failed to fetch https://updates.software-univention.de/4.3/maintained/4.3-2/amd64/InRelease Could not resolve host: updates.software-univention.de
W: Failed to fetch https://updates.software-univention.de/4.3/maintained/4.3-3/all/InRelease Could not resolve host: updates.software-univention.de
W: Failed to fetch https://updates.software-univention.de/4.3/maintained/4.3-3/amd64/InRelease Could not resolve host: updates.software-univention.de
W: Failed to fetch https://updates.software-univention.de/4.3/maintained/4.3-4/all/InRelease Could not resolve host: updates.software-univention.de
W: Failed to fetch https://updates.software-univention.de/4.3/maintained/4.3-4/amd64/InRelease Could not resolve host: updates.software-univention.de
W: Failed to fetch https://updates.software-univention.de/4.3/maintained/4.3-5/all/InRelease Could not resolve host: updates.software-univention.de
W: Failed to fetch https://updates.software-univention.de/4.3/maintained/4.3-5/amd64/InRelease Could not resolve host: updates.software-univention.de
W: Failed to fetch https://updates.software-univention.de/4.4/maintained/4.4-0/all/InRelease Could not resolve host: updates.software-univention.de
W: Failed to fetch https://updates.software-univention.de/4.4/maintained/4.4-0/amd64/InRelease Could not resolve host: updates.software-univention.de
W: Failed to fetch https://updates.software-univention.de/4.4/maintained/4.4-1/all/InRelease Could not resolve host: updates.software-univention.de
W: Failed to fetch https://updates.software-univention.de/4.4/maintained/4.4-1/amd64/InRelease Could not resolve host: updates.software-univention.de
W: Failed to fetch https://updates.software-univention.de/4.4/maintained/4.4-2/all/InRelease Could not resolve host: updates.software-univention.de
W: Failed to fetch https://updates.software-univention.de/4.4/maintained/4.4-2/amd64/InRelease Could not resolve host: updates.software-univention.de
W: Failed to fetch https://updates.software-univention.de/4.4/maintained/4.4-3/all/InRelease Could not resolve host: updates.software-univention.de
W: Failed to fetch https://updates.software-univention.de/4.4/maintained/4.4-3/amd64/InRelease Could not resolve host: updates.software-univention.de
W: Failed to fetch https://updates.software-univention.de/4.4/maintained/4.4-4/all/InRelease Could not resolve host: updates.software-univention.de
W: Failed to fetch https://updates.software-univention.de/4.4/maintained/4.4-4/amd64/InRelease Could not resolve host: updates.software-univention.de
W: Some index files failed to download. They have been ignored, or old ones used instead.

Is your system able to resolve external domains? What does

dig updates.software-univention.de

and

dig example.com

return?

Administrator@DC:/$ dig updates.software-univention.de

; <<>> DiG 9.10.3-P4-Univention <<>> updates.software-univention.de
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 23861
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 13, ADDITIONAL: 4

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 4096
;; QUESTION SECTION:
;updates.software-univention.de. IN A

;; ANSWER SECTION:
updates.software-univention.de. 3358 IN A 176.9.114.147

;; AUTHORITY SECTION:
. 71429 IN NS m.root-servers.net.
. 71429 IN NS f.root-servers.net.
. 71429 IN NS h.root-servers.net.
. 71429 IN NS d.root-servers.net.
. 71429 IN NS k.root-servers.net.
. 71429 IN NS a.root-servers.net.
. 71429 IN NS i.root-servers.net.
. 71429 IN NS b.root-servers.net.
. 71429 IN NS g.root-servers.net.
. 71429 IN NS l.root-servers.net.
. 71429 IN NS e.root-servers.net.
. 71429 IN NS j.root-servers.net.
. 71429 IN NS c.root-servers.net.

;; ADDITIONAL SECTION:
B.ROOT-SERVERS.net. 245099 IN AAAA 2001:500:200::b
E.ROOT-SERVERS.net. 244861 IN AAAA 2001:500:a8::e
G.ROOT-SERVERS.net. 244988 IN AAAA 2001:500:12::d0d

;; Query time: 5 msec
;; SERVER: 10.10.10.8#53(10.10.10.8)
;; WHEN: Wed Jan 06 16:50:07 IST 2021
;; MSG SIZE rcvd: 389

Administrator@DC:/$ dig example.com

; <<>> DiG 9.10.3-P4-Univention <<>> example.com
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 61997
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 13, ADDITIONAL: 27

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 4096
;; QUESTION SECTION:
;example.com. IN A

;; ANSWER SECTION:
example.com. 21436 IN A 93.184.216.34

;; AUTHORITY SECTION:
com. 159209 IN NS e.gtld-servers.net.
com. 159209 IN NS f.gtld-servers.net.
com. 159209 IN NS m.gtld-servers.net.
com. 159209 IN NS a.gtld-servers.net.
com. 159209 IN NS l.gtld-servers.net.
com. 159209 IN NS d.gtld-servers.net.
com. 159209 IN NS c.gtld-servers.net.
com. 159209 IN NS h.gtld-servers.net.
com. 159209 IN NS g.gtld-servers.net.
com. 159209 IN NS b.gtld-servers.net.
com. 159209 IN NS j.gtld-servers.net.
com. 159209 IN NS i.gtld-servers.net.
com. 159209 IN NS k.gtld-servers.net.

;; ADDITIONAL SECTION:
a.gtld-servers.net. 159209 IN A 192.5.6.30
a.gtld-servers.net. 159209 IN AAAA 2001:503:a83e::2:30
b.gtld-servers.net. 159209 IN A 192.33.14.30
b.gtld-servers.net. 159209 IN AAAA 2001:503:231d::2:30
c.gtld-servers.net. 159209 IN A 192.26.92.30
c.gtld-servers.net. 159209 IN AAAA 2001:503:83eb::30
d.gtld-servers.net. 159209 IN A 192.31.80.30
d.gtld-servers.net. 159209 IN AAAA 2001:500:856e::30
e.gtld-servers.net. 159209 IN A 192.12.94.30
e.gtld-servers.net. 159209 IN AAAA 2001:502:1ca1::30
f.gtld-servers.net. 159209 IN A 192.35.51.30
f.gtld-servers.net. 159209 IN AAAA 2001:503:d414::30
g.gtld-servers.net. 159209 IN A 192.42.93.30
g.gtld-servers.net. 159209 IN AAAA 2001:503:eea3::30
h.gtld-servers.net. 159209 IN A 192.54.112.30
h.gtld-servers.net. 159209 IN AAAA 2001:502:8cc::30
i.gtld-servers.net. 159209 IN A 192.43.172.30
i.gtld-servers.net. 159209 IN AAAA 2001:503:39c1::30
j.gtld-servers.net. 159209 IN A 192.48.79.30
j.gtld-servers.net. 159209 IN AAAA 2001:502:7094::30
k.gtld-servers.net. 159209 IN A 192.52.178.30
k.gtld-servers.net. 159209 IN AAAA 2001:503:d2d::30
l.gtld-servers.net. 159209 IN A 192.41.162.30
l.gtld-servers.net. 159209 IN AAAA 2001:500:d937::30
m.gtld-servers.net. 159209 IN A 192.55.83.30
m.gtld-servers.net. 159209 IN AAAA 2001:501:b1f9::30

;; Query time: 4 msec
;; SERVER: 10.10.10.8#53(10.10.10.8)
;; WHEN: Wed Jan 06 16:50:52 IST 2021
;; MSG SIZE rcvd: 852

I saw that you used apt to upgrade while the supported tool is univention-upgrade.
Would you mind trying it again as the resolving worked 2 hours ago? Perharps there were some networking difficulties during the first run.