A major J:COM outage disrupted internet service across large parts of Japan on September 23, 2026. J:COM confirmed that its internet service was unavailable and said restoration work was underway, but the company had not initially identified the cause or given a firm restoration time.
The incident also affected customer-support access, making it difficult for some subscribers to contact the company. Reports later indicated that the disruption did not affect Hokkaido and Kyushu in the same way, so “nationwide” should not be interpreted as every J:COM service being down in every prefecture.
What Happened During the J:COM Outage?
J:COM said its internet service experienced a system failure beginning at about 8:55 a.m. on September 23. The company’s support channels were also difficult to reach during the incident.
J:COM’s official outage information later listed a broad disruption affecting internet connectivity. At the time of reporting, the company was still working on restoration and had not announced a confirmed technical cause.
Yomiuri reported that J:COM NET had approximately 4.62 million contracts nationwide. That figure should not be confused with the number of customers actually affected by the outage, which remained.
Why DNS Became a Key Clue
DNS, or Domain Name System, translates website names into the numerical addresses computers use to locate online services.
That makes DNS an important part of everyday internet access. If an ISP’s DNS resolver stops responding correctly, a user’s physical connection may still be available while websites appear unreachable.
During the J:COM outage, users on social media reported that switching their DNS settings to public resolvers sometimes restored access. ITmedia also reported these user experiences, while noting that a J:COM DNS problem was only a possibility because the company had not confirmed the cause.
That distinction matters. Changing DNS can be a useful workaround for a DNS failure, but successful DNS changes do not prove that DNS was the root cause of the entire J:COM incident.
Public DNS addresses reported as workarounds
| DNS provider | Primary DNS | Secondary DNS |
|---|---|---|
| Google Public DNS | 8.8.8.8 | 8.8.4.4 |
| Cloudflare DNS | 1.1.1.1 | — |
These addresses were among the public DNS services users reported trying during the outage.
If the underlying ISP connection is actually down, changing DNS will not restore it. It can help only when DNS resolution is the part of the connection path that is failing.
Why Other Cable Operators Can Be Affected
The incident also highlights how internet services can depend on infrastructure outside the company customers see on their bills.
Regional cable operators may maintain local networks while relying on larger providers for parts of their upstream connectivity or related infrastructure. A failure in shared systems can therefore produce problems across multiple services.
Reports during the incident indicated that regional cable operators also experienced related connectivity or server problems. The exact number of independently affected operators should be treated as until each case is confirmed.
For network operators, this is a redundancy issue. Having backup equipment in one location is not enough if several services ultimately depend on the same upstream system.
What Users Can Do During a DNS-Related Outage
For ordinary users, the safest first step is to determine whether the problem affects only one device or the entire home connection.
If other devices show the same problem, restarting the router or checking the provider’s official outage information can help establish whether the problem is local or network-wide.
If the ISP connection itself remains available but DNS appears to be failing, users can temporarily test a public resolver such as Google Public DNS or Cloudflare.
A second internet connection is more useful when the ISP’s network is completely unavailable. For remote workers, keeping mobile tethering available can provide a separate path to the internet instead of relying entirely on the same fixed-line provider.
What Remains Unknown
The most important unanswered question is the technical cause of the J:COM outage.
J:COM had confirmed the system failure but had not publicly established whether the underlying problem involved DNS, software, hardware, configuration or another network component.
Claims of a cyberattack should also be treated as unconfirmed unless J:COM or an appropriate authority provides evidence.
The final number of affected users, the complete restoration timeline and the performance of J:COM’s backup systems also require further verification.
What Readers Should Know
The September 23 J:COM outage shows why a large internet service can experience a problem that looks like a complete loss of connectivity even when some underlying network functions may still be operating.
Public DNS services offered a workaround for some users, but that does not establish DNS as the confirmed cause. J:COM’s own statements continued to describe the event as a system failure while restoration and investigation were underway.
For users, the practical lesson is simple: keep official outage information available, know how to test an alternative DNS resolver, and maintain a second internet connection if losing connectivity would interrupt important work..
