Monitored networks

ASNs, prefixes, and why the network a figure describes is always named.

Monitoring starts from an autonomous system number. An ASN identifies a network on the public internet: the set of address blocks one operator announces and is responsible for routing.

Why the ASN is the unit

It is the only identifier in this chain that is public and checkable. A provider's brand, its website and its marketing claims are all things it tells us. What it announces to the internet is a matter of record, visible to anybody, and impossible to fake without operational consequences.

Starting from the ASN also means the target list is derived rather than supplied. A provider cannot hand us a curated list of addresses it knows are healthy.

From ASN to targets

Public routing data gives the prefixes an ASN announces. A bounded sample of addresses from those prefixes becomes the target list. It is a sample, not an enumeration: measuring every address in a large provider's space would be both pointless and indistinguishable from scanning.

The announced footprint and the monitored targets are therefore two different numbers, and the status page reports them as two different numbers. The first is how much address space the provider announces; the second is how many addresses are actually being probed.

Why the network is always named

Every published figure says which autonomous system it describes, by number and by operator name where the registry knows one.

This is not decoration. A reseller and its upstream are different autonomous systems behind one brand, and availability measured on the upstream says very little about the service the reseller sells. A reader deciding whether a number is about the thing they are buying needs to see which network it came from.

Where the registry does not know an operator for a number, the number is printed on its own. No operator name is inferred, because a plausible-looking wrong one is worse than a bare number.

Multiple networks

A provider may register several ASNs, and larger ones usually do. All of them are measured, and the status page lists them. The headline figure covers the registered set; the breakdown shows how each network is doing, which is where a provider with one healthy network and one struggling one becomes visible.

Keeping the register right

An ASN that stops being announced, or that changes hands, makes a provider's monitoring describe somebody else's network. Provider managers can change their registered ASNs from the provider editor, and are the right people to do it: they know when their network changes and we do not.