Website Availability in Japan
Submarine cables, ISP health and blocking risks that decide whether a website loads in Japan. Checked against live measurement data.
Wondering whether a website is down for everyone or just unreachable from Japan? The answer usually hides in the physical layer of the internet. Japan 🇯🇵 connects to the global network through 52 submarine cable systems that come ashore at 68 landing stations, and its national domain zone is .jp. Every request from a user in Japan to a foreign server, and every request from abroad to a site hosted in Japan, physically travels over these systems or their terrestrial backhaul.
This page summarizes what our measurement network knows about internet connectivity in Japan: which cables serve the country, how its leading internet providers are performing, and what can make a website appear offline for users there while it works everywhere else.
Current connectivity status in Japan
As of our latest hourly measurement cycle, the national internet signal of Japan is operating normally (BGP visibility and active probing dip: 0% against the 24-hour baseline). National-level signals catch large events; an individual website can still be unreachable for local reasons, which is what the availability checker above is for.
Connectivity for most users in Japan is provided by a small group of networks:
| Provider | ASN | Share of users | Status |
|---|---|---|---|
| KDDI - KDDI CORPORATION | AS2516 | 18.8% | No recent anomaly |
| GIGAINFRA - SoftBank Corp. | AS17676 | 17.2% | No recent anomaly |
| OCN - NTT DOCOMO BUSINESS,Inc. | AS4713 | 10.8% | No recent anomaly |
| docomo - NTT DOCOMO, INC. | AS9605 | 6.2% | No recent anomaly |
| OPTAGE - OPTAGE Inc. | AS17511 | 4.4% | No recent anomaly |
If a website fails to load only for customers of one of these providers, the problem is almost always local: DNS resolution inside that network, ISP-level filtering, or a routing issue, rather than the website itself being down.
Submarine cables that connect Japan to the internet
The following systems land in Japan. Cable length is a rough proxy for how much of the world a system reaches: long trunks connect continents, short ones link neighbors. Our monitors registered no significant latency anomalies on these systems in the last 30 days.
| Cable system | Length | In service since |
|---|---|---|
| EAC-C2C | 36,500 km | 2002 |
| FLAG Europe-Asia (FEA) | 28,000 km | 1997 |
| Tata TGN-Pacific | 22,300 km | 2002 |
| Pacific Crossing-1 (PC-1) | 21,000 km | 1999 |
| APCN-2 | 19,000 km | 2001 |
| Trans-Pacific Express (TPE) Cable System | 17,968 km | 2008 |
| JUPITER | 14,557 km | 2020 |
| New Cross Pacific (NCP) Cable System | 13,618 km | 2018 |
| Australia-Japan Cable (AJC) | 12,700 km | 2001 |
| E2A | 12,500 km | 2029 |
| Apricot | 11,972 km | 2025 |
| JUNO | 11,710 km | 2025 |
Plus 40 more systems, mostly regional links. Live health data for every cable is available on the linked pages.
How resilient is Japan to cable failures?
With 52 cable systems across 68 landing stations, Japan has one of the most redundant internet connections in the world. Traffic can reroute across many independent systems, so a single cable fault rarely affects end users. Repairs at sea typically take one to several weeks, because a specialized cable ship has to locate the fault, lift the cable and splice it on deck.
Why a website may not load in Japan
When a site works in other countries but fails in Japan, the usual suspects are, in order of likelihood: a DNS problem inside a local ISP, a content delivery network misrouting users in Japan to an unhealthy edge node, a routing or peering issue between local networks and the site's host, and finally a submarine cable incident affecting the whole region.
Our DNS measurements have not flagged systematic national filtering in Japan, although individual ISPs and corporate networks can still block specific resources.
Neighbors on the same cables
These countries share submarine cable systems with Japan, so a major cable incident can affect them together:
🇰🇷 South Korea (13 shared) · 🇸🇬 Singapore (11 shared) · 🇺🇸 United States (11 shared) · 🇵🇭 Philippines (9 shared) · 🇲🇾 Malaysia (7 shared) · 🇹🇭 Thailand (4 shared)
See the full list on the website availability by country hub.
Frequently asked questions
How do I check if a website is down in Japan?
Enter the URL into the free Global Availability Checker on this site. It compares measurement data from 80+ countries, including probes relevant to Japan, and shows in seconds whether the site is down everywhere or only unreachable from specific regions.
How many submarine cables connect Japan?
Japan is served by 52 submarine cable systems landing at 68 coastal stations. The longest systems are EAC-C2C, FLAG Europe-Asia (FEA), Tata TGN-Pacific.
Why does a website work in other countries but not in Japan?
The most common causes are DNS failures inside a local ISP, CDN edge problems, routing issues between Japan and the hosting network, national filtering, and submarine cable faults. Testing the URL from multiple countries immediately narrows down which one it is.
Who are the largest internet providers in Japan?
The leading networks by user share are KDDI - KDDI CORPORATION, GIGAINFRA - SoftBank Corp., OCN - NTT DOCOMO BUSINESS,Inc.. Together they carry the majority of consumer traffic, so a problem inside any of them affects a large share of users in Japan.
Can a single cable failure disconnect Japan?
No. With 52 independent cable systems, traffic reroutes automatically around a single fault.
Does Japan block websites?
We have not detected systematic national filtering in Japan, but individual ISPs and corporate networks can still block specific sites.
Data: GeoCables submarine cable telemetry, RIPE Atlas measurements, IODA national signals, APNIC user estimates. Numbers refresh automatically; last update July 11, 2026.