What is a looking glass?
A looking glass is a public, read-only window into an operator's router. It lets you check BGP routes, ping and traceroute from the perspective of a given network.
Last updated:
A looking glass is a public diagnostic tool that gives read-only insight into a network's router or routing table. It lets an outside observer see how a particular operator views the internet from its own vantage point: what BGP routes it has to a given prefix, what the AS_PATH is, and how reachability and latency to a chosen target look. A looking glass is standard equipment for operators and internet exchanges. Most often it is used to diagnose routing and connectivity problems between networks.
What you can check in a looking glass
A typical looking glass exposes a set of safe, non-intrusive commands run from the operator's router. The most common are:
- Ping (IPv4 and IPv6): check reachability and latency to a given address.
- Traceroute or MTR: trace the packet path and spot where packet loss starts to rise.
- A BGP route query: how the router selects a path to a prefix, its AS_PATH and attributes.
- A view of advertised and received prefixes from the perspective of a given location.
What a looking glass is for
A looking glass is used most often for diagnostics from a remote network's perspective. From your own computer you only see the internet the way your provider routes it, whereas a looking glass lets you look at the same problem through the eyes of another operator in a different city or country. Engineers use it to verify that a new BGP advertisement has propagated correctly, check which way traffic flows to a destination, compare latency from different locations or determine on whose side a connectivity problem originates.
A looking glass versus other tools
A looking glass complements other tools but does not replace them. A traceroute run from your own host shows the path in one direction from a single point, while a looking glass gives a view from several of an operator's locations. PeeringDB describes where a network is present and what its policy is, but does not show the current state of routes. Public route collectors such as RIPE RIS or RouteViews gather historical BGP data, whereas a looking glass answers the current-state question: how a router sees a given destination at that moment. Because it runs strictly read-only, it is safe and cannot change the network's configuration.
The AS202520 SkyPass looking glass
AS202520 SkyPass provides a public looking glass where you can run ping and MTR for IPv4 and IPv6 from our infrastructure, including a location in Wrocław. With it you can check the latency and path from our network to your resources, verify connectivity before setting up peering, or diagnose a routing problem between our network and yours. The tool is available without login and operates in read-only mode.
Frequently asked questions
What is a looking glass?
It is a public, read-only tool that shows how a given operator's router sees the internet: BGP routes, the AS_PATH, and the results of ping and traceroute from the perspective of its network.
How do I check the BGP route to my network?
Use an operator's looking glass and run a route query for your prefix. You will see whether it is reachable, what its AS_PATH is and which way traffic flows to it.
Is a looking glass safe?
Yes. It runs strictly read-only and exposes only non-intrusive diagnostic commands such as ping, traceroute and route views. It cannot change the network's configuration.
Where can I find the AS202520 SkyPass looking glass?
AS202520 SkyPass provides its own looking glass with ping and MTR tests for IPv4 and IPv6, including from a location in Wrocław, available without login.