AS58305: the SYN-US SYN network

AS58305 is an internet Autonomous System operated by SYN-US SYN (the United Kingdom). Here is what that means and why this number may show up when you investigate a connection on your network.

What is AS58305?

An Autonomous System (ASN) is a block of networks under a single control with its own routing policy on the internet. The number AS58305 was assigned to SYN-US SYN by an RIR (regional internet registry). All traffic entering or leaving that network is announced under this number.

Reach on the internet

AS58305 currently announces 3 IPv4 block(s), totaling about 2 thousand addresses (2,048 in all), registered in the United Kingdom. Services from SYN-US SYN are reached through these addresses.

What it means to see AS58305 on your network

When you investigate where a connection from your computer or phone comes from (or goes to), you may find AS58305. That means the other end sits on the SYN-US SYN network (the United Kingdom). 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.