% APNIC found the following authoritative answer from: whois.ripe.net

% This is the RIPE Database query service.
% The objects are in RPSL format.
%
% The RIPE Database is subject to Terms and Conditions.
% See https://apps.db.ripe.net/docs/HTML-Terms-And-Conditions

% Note: this output has been filtered.
%       To receive output for a database update, use the "-B" flag.

% Information related to '217.28.80.0 - 217.28.87.255'

% Abuse contact for '217.28.80.0 - 217.28.87.255' is 'abuse@fiber.cz'

inetnum:        217.28.80.0 - 217.28.87.255
netname:        FIBER-NETWORKS-APA
descr:          FIBER Networks customers
country:        CZ
org:            ORG-FNs4-RIPE
admin-c:        JK6086-RIPE
admin-c:        LM1397-RIPE
tech-c:         JK6086-RIPE
tech-c:         LM1397-RIPE
status:         ASSIGNED PA
mnt-by:         MNT-FIBERCZ
created:        2016-01-26T17:27:34Z
last-modified:  2016-01-26T17:27:34Z
source:         RIPE

organisation:   ORG-FNs4-RIPE
org-name:       FIBER Network s.r.o.
country:        CZ
org-type:       LIR
address:        Cimburkova 369/16
address:        130 00
address:        Prague 3
address:        CZECH REPUBLIC
phone:          +420222742742
fax-no:         +420222742744
abuse-c:        AFBR1
mnt-ref:        RIPE-NCC-HM-MNT
mnt-ref:        MNT-FIBERCZ
mnt-by:         RIPE-NCC-HM-MNT
mnt-by:         MNT-FIBERCZ
created:        2010-10-25T13:22:51Z
last-modified:  2020-12-16T13:18:11Z
source:         RIPE # Filtered

person:         Jiri Kobilak
address:        FIBER Network
address:        Cimburkova 369/16
address:        13000 Praha 3
address:        Czech Republic / EU
nic-hdl:        JK6086-RIPE
created:        2010-10-27T23:27:39Z
last-modified:  2010-11-10T18:23:34Z
source:         RIPE # Filtered
phone:          +420222742742
mnt-by:         MNT-COBOOL

person:         Lukas Mesani
phone:          +420-222-742-740
address:        Czech Republic
nic-hdl:        LM1397-RIPE
mnt-by:         MNT-FRODO
created:        2006-06-07T13:57:53Z
last-modified:  2020-03-03T14:23:08Z
source:         RIPE

% Information related to '217.28.80.0/21AS51800'

route:          217.28.80.0/21
descr:          CZFIBERNET1
origin:         AS51800
mnt-by:         MNT-FIBERCZ
created:        2010-11-09T17:53:32Z
last-modified:  2010-11-09T17:53:32Z
source:         RIPE

% This query was served by the RIPE Database Query Service version 1.111 (ABERDEEN)

Search for
IP address lookups			Miscellaneous queries
-l	1st level less specific		-i	Inverse attributes	None admin-c admin-c,tech-c,zone-c author cross-mnt cross-nfy local-as mbrs-by-ref member-of mnt-by mnt-lower mnt-nfy mnt-routes notify nserver origin person referral-by rev-srv sub-dom tech-c upd-to zone-c
-L	All less specific		-T	Object types	All as-block as-set aut-num domain filter-set inet-rtr inet6num inetnum irt key-cert mntner peering-set person role route route-set rtr-set
-m	1st level more specific
-M	All more specific		Query hints Include "AS" in front of an AS number. Example: AS4808 Include "-t" (template only) or "-v" (template and description) in front of an object name to view the template Example: -t inetnum
-x	Exact match only
-d	Associated reverse domain