AS27521: the CATCOMM-ASN network

AS27521 is an internet Autonomous System operated by CATCOMM-ASN (the United States). Here is what that means and why this number may show up when you investigate a connection on your network.

What is AS27521?

An Autonomous System (ASN) is a block of networks under a single control with its own routing policy on the internet. The number AS27521 was assigned to CATCOMM-ASN by an RIR (regional internet registry). All traffic entering or leaving that network is announced under this number.

Reach on the internet

AS27521 currently announces 8 IPv4 block(s), totaling about 6.4 thousand addresses (6,400 in all), registered in the United States. Services from CATCOMM-ASN are reached through these addresses.

What it means to see AS27521 on your network

When you investigate where a connection from your computer or phone comes from (or goes to), you may find AS27521. That means the other end sits on the CATCOMM-ASN network (the United States). 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.