AS57021: the NTP-SE Anycasted NTP services from Netnod IXPs network

AS57021 is an internet Autonomous System operated by NTP-SE Anycasted NTP services from Netnod IXPs (Sweden). Here is what that means and why this number may show up when you investigate a connection on your network.

What is AS57021?

An Autonomous System (ASN) is a block of networks under a single control with its own routing policy on the internet. The number AS57021 was assigned to NTP-SE Anycasted NTP services from Netnod IXPs by an RIR (regional internet registry). All traffic entering or leaving that network is announced under this number.

Reach on the internet

AS57021 currently announces 2 IPv4 block(s), totaling about 1.8 thousand addresses (1,792 in all), registered in Sweden. Services from NTP-SE Anycasted NTP services from Netnod IXPs are reached through these addresses.

What it means to see AS57021 on your network

When you investigate where a connection from your computer or phone comes from (or goes to), you may find AS57021. That means the other end sits on the NTP-SE Anycasted NTP services from Netnod IXPs network (Sweden). 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.