Korea Telecom IP Ranges
Korea Telecom runs AS4766, the number close to half of South Korea's internet users sit behind. Its registry record is unusual for this section: it is held by KRNIC, the national internet registry operated by the Korea Internet and Security Agency, and APNIC serves only a partial mirror of it, so a query to APNIC's RDAP service for AS4766 is redirected to krnic.rdap.apnic.net. What comes back is the as-name KIXS-AS-KR-KR, the description Korea Telecom, and administrative and technical contacts filed as AS Manager and IP Manager at KT Head Office on Buljeong-ro in Seongnam. APNIC Labs ranks the network first in the country at 24,008,724 estimated users, 46.96 percent of the Korean base.
- Provider
- Korea Telecom
- Primary ASN
- AS4766
- Category
- ISP
- Headquarters
- Seongnam, South Korea
- Announced IPv4 prefixes
- 2147
- Registry
- APNIC
Known IP ranges
These prefixes are currently announced to the global routing table by AS4766 (KIXS-AS-KR-KR - Korea Telecom). Prefix sets change over time - use WHOIS Lookup for the authoritative record on any specific address.
59.0.0.0/11
121.128.0.0/11
125.128.0.0/11
121.160.0.0/11
121.176.0.0/12
183.112.0.0/12
125.128.0.0/12
125.144.0.0/12
121.160.0.0/12
118.48.0.0/12
2400:130::/30
2400:144::/30
2400:140::/30 (IPv6)
What does a Korea Telecom IP mean in a privacy test?
An address on AS4766 is almost certainly a Korean line, because this one number carries close to half the country's users, but it is not necessarily a KT retail line. RIPEstat counts 571 downstream neighbours against 60 upstream, and KT sub-allocates out of its own consumer space to those customers: inside 121.160.0.0/11 alone, RADB holds dozens of /24 and /22 route objects originated not by AS4766 but by AS9530, AS55589, AS17862, AS45967 and AS23582 among others. The address registry will not show you that split, because the KRNIC mirror stops at the allocation and a lookup inside that /11 returns the parent block named KORNET-KR and nothing more specific. Reverse DNS adds nothing either, since sampled addresses across three separate KT blocks have no PTR record at all. So a Korea Telecom result tells you the traffic came out in Korea on the largest domestic network, and the routing registry rather than the address registry is where the next detail lives.
Why a Korea Telecom lookup returns so little
The thinness of the public record is structural rather than accidental. Korea is one of a small number of economies with a national internet registry, and KT's resources are registered with KRNIC, which the Korea Internet and Security Agency operates. APNIC mirrors that data only partially and says so in a notice attached to every result, directing anyone wanting more detail to the KRNIC whois server at whois.kisa.or.kr. The consequence shows in the object itself: the RDAP record for AS4766 carries no registration event at all, and the address objects behave the same way. Contacts are generic operator roles rather than named people, with kornet_ip@kt.com as the address of record, and abuse is routed to IRT-KRNIC-KR at the registry rather than to KT directly. The registry also still records the holder as Korea Telecom, while KT's own PeeringDB entry is filed under the current corporate name, KT Corporation, with the network known as KORNET.
What KT does publish sits outside the registry. That PeeringDB entry gives the IRR as-set as AS-KORNET, states 20-50Tbps of traffic at global scope, classifies the network as Cable/DSL/ISP, and describes a selective peering policy that does not require a contract, across 14 exchanges and 8 facilities. Route objects for its space are registered in RADB rather than in an APNIC-region routing registry, with 121.160.0.0/11 and 121.160.0.0/12 both appearing there originated by AS4766 alongside the customer objects inside them. There is no geofeed. APNIC supports a geofeed: attribute on inetnum objects pointing at an RFC 8805 CSV over HTTPS, and KT has not filled one in, so the country code KR on the allocation plus whatever a commercial database has measured is all there is to place a KT address with.
Separating KT retail traffic from a customer network
Reverse DNS is not the tool for this. Sampled addresses in 121.160.0.0/11, 125.128.0.0/11 and 59.0.0.0/11 all returned NXDOMAIN, so no hostname convention marks a home line, a business circuit or a router interface. Nor will whois separate them: KT registers no product-labelled child objects, so the most specific record you can retrieve for a retail address is the KORNET-KR allocation itself, an ALLOCATED PORTABLE /11 covering just over two million addresses.
The routing registry is where the distinction actually lives, and it is worth checking before you attribute anything. KT hands pieces of its consumer allocations to transit and colocation customers who register their own route objects over them: 121.170.176.0/24 through 121.170.179.0/24 are originated by AS9530, 121.170.28.0/22 by AS55589, 121.187.64.0/20 by AS17862, 121.168.252.0/22 by AS23582, all inside a block whose inetnum says nothing but Korea Telecom. So an address that resolves to AS4766 in a live BGP lookup is KT's own access space, retail or small business, while an address sitting in the same /11 that resolves to a different origin belongs to that customer and KT is only the covering registrant. If you need anything finer than that, the operator-side source is the KRNIC whois server APNIC's own notice points you at; there is nothing more to extract from the mirrored copy.
Related tools
Frequently asked questions
What IP ranges does Korea Telecom use?
KT announces its address space under AS4766, recorded as KIXS-AS-KR-KR. The largest blocks currently in the routing table are listed above, and the ones sampled are registered under the netname KORNET-KR. The authoritative record is held by KRNIC, the Korean national internet registry, and APNIC carries only a partial mirror of it.
Why does a whois lookup on a Korea Telecom address return so little detail?
Because APNIC only partially mirrors KRNIC's data and says so in a notice attached to the result. A lookup returns the parent allocation, its netname and a generic operator contact, with no assignment-level records and no registration event on the ASN object. For fuller data the mirrored record itself points at the KRNIC whois server at whois.kisa.or.kr.
Why does a Korea Telecom address show up in my VPN or leak test?
Because the request left over your Korean line rather than through a tunnel. On a DNS leak test it means a resolver inside KT's network answered your queries, which is the default on a KT connection. If a VPN was supposed to be carrying that traffic, it is not.
Is every address on AS4766 a home connection?
No. AS4766 is both Korea's largest access network and a transit provider with 571 downstream neighbours, and KT sub-allocates parts of its consumer blocks to customers who announce them under their own ASNs. RADB shows dozens of such route objects inside 121.160.0.0/11 with origins including AS9530, AS55589 and AS17862, so an address inside a KORNET block does not always resolve to AS4766.
Is AS4766 the only Korea Telecom network number?
No. KT also holds AS3559, recorded through the same KRNIC mirror as KORNET-AS-KR-KR with the same Korea Telecom description and the same KT Head Office contacts. AS4766 is the number that carries the bulk of the measured user population, but a Korean address described as Korea Telecom in a lookup will not always be announced from it.