AS9999: the ATTOKYO AT TOKYO Corporation network

AS9999 is an internet Autonomous System operated by ATTOKYO AT TOKYO Corporation (Japan). Here is what that means and why this number may show up when you investigate a connection on your network.

What is AS9999?

An Autonomous System (ASN) is a block of networks under a single control with its own routing policy on the internet. The number AS9999 was assigned to ATTOKYO AT TOKYO Corporation by an RIR (regional internet registry). All traffic entering or leaving that network is announced under this number.

Reach on the internet

AS9999 currently announces 10 IPv4 block(s), totaling about 20.2 thousand addresses (20,224 in all), registered in Japan. Services from ATTOKYO AT TOKYO Corporation are reached through these addresses.

What it means to see AS9999 on your network

When you investigate where a connection from your computer or phone comes from (or goes to), you may find AS9999. That means the other end sits on the ATTOKYO AT TOKYO Corporation network (Japan). It can be legitimate — a cloud service, an ISP, a CDN — or an unexpected connection worth checking.

How to see every connection and network your devices reach

Tracing one connection's ASN at a time is tedious. Sentinela, by PC Monitor, maps the devices on your network, shows what is exposed to the internet and helps flag suspicious connections and devices — running on your Windows. Meet Sentinela.