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

% [whois.apnic.net]
% Whois data copyright terms    http://www.apnic.net/db/dbcopyright.html

% Information related to '203.151.128.0 - 203.151.128.255'

% Abuse contact for '203.151.128.0 - 203.151.128.255' is 'op-network@inet.co.th'

inetnum:        203.151.128.0 - 203.151.128.255
netname:        INET-TH
descr:          Internet Thailand Public Company Limited
country:        TH
admin-c:        ITP2-AP
tech-c:         CW2606-AP
abuse-c:        AI358-AP
status:         ALLOCATED NON-PORTABLE
mnt-by:         MAINT-TH-INET
mnt-irt:        IRT-INET-TH
last-modified:  2023-08-09T04:09:18Z
source:         APNIC

irt:            IRT-INET-TH
address:        Internet Thailand Public Company Limited
address:        1768 Thai Summit Tower, 10th -12th Floor and IT Floor
address:        New Petchburi Road, Khwaeng Bang Kapi,
address:        Khet Huay Khwang, Bangkok 10310 Thailand
e-mail:         op-network@inet.co.th
abuse-mailbox:  op-network@inet.co.th
admin-c:        TY1494-AP
tech-c:         IP219-AP
auth:           # Filtered
remarks:        op-network@inet.co.th was validated on 2024-08-28
mnt-by:         MAINT-TH-INET
last-modified:  2024-09-19T08:38:10Z
source:         APNIC

role:           ABUSE INETTH
country:        ZZ
address:        Internet Thailand Public Company Limited
address:        1768 Thai Summit Tower, 10th -12th Floor and IT Floor
address:        New Petchburi Road, Khwaeng Bang Kapi,
address:        Khet Huay Khwang, Bangkok 10310 Thailand
phone:          +000000000
e-mail:         op-network@inet.co.th
admin-c:        TY1494-AP
tech-c:         IP219-AP
nic-hdl:        AI358-AP
remarks:        Generated from irt object IRT-INET-TH
remarks:        op-network@inet.co.th was validated on 2024-08-28
abuse-mailbox:  op-network@inet.co.th
mnt-by:         APNIC-ABUSE
last-modified:  2024-09-19T08:38:44Z
source:         APNIC

person:         Chanon Watcharachinvong
address:        1768 Thai Summit Tower, 10-ITFl., New Petchaburi Road,Khwaeng Bang Kapi, Khet Huay Khwang, Bangkok 10310
country:        TH
phone:          +66-2257-7111
e-mail:         chanon.wa@inet.co.th
nic-hdl:        CW2606-AP
mnt-by:         MAINT-ITSC-AP
last-modified:  2023-08-09T04:05:42Z
source:         APNIC

person:         INTERNET THAILAND PCL
address:        1768 Thai Summit Tower, 10-ITFl., New Petchaburi Road,Khwaeng Bang Kapi, Khet Huay Khwang, Bangkok 10310
country:        TH
phone:          +66-2257-7111
e-mail:         op-network@inet.co.th
nic-hdl:        ITP2-AP
mnt-by:         MAINT-TH-INET
last-modified:  2022-06-13T06:34:28Z
source:         APNIC

% Information related to '203.151.128.0/21AS4618'

route:          203.151.128.0/21
origin:         AS4618
descr:          Internet Thailand Company Ltd.
                1768 IFCT Tower, 10th-12th FL
                IT Floor New Petchburi Road
                Khwaeng Bang Kapi
                Khet Huay Khwang
mnt-by:         MAINT-TH-INET
last-modified:  2020-11-19T08:24:19Z
source:         APNIC

% This query was served by the APNIC Whois Service version 1.88.25 (WHOIS-AU3)

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