Overview
A Looking Glass is a tool provided by internet service providers to gather information on network health. A server is provided to view routing information from a specified location and made publicly accessible. Publicly accessible Looking Glass servers are typically run by ISPs such as Level3, XO, and NTT.
Use Case
There are times when a node is not working properly. Traceroutes and pings help diagnose a node’s health. Since the path going to and coming from a node can be different, it is best practice to get traceroutes and pings in both directions.
If you believe there is an issue with the health of a Catchpoint node, it is recommended to get traceroutes and pings to the node to ensure a clear path when communicating from the network to the node. An ISP's Looking Glass server allows you to do this. It will create network diagnostics from the provider's network to the Catchpoint node.
Looking Glass Servers
Listed below are some links to Looking Glass Servers:
http://aurora.on.tac.net/ (Telus)
http://lg.zayo.com/lg.cgi (Zayo)
http://lg.level3.net/ (Level3/Centurylink)
https://www.us.ntt.net/support/looking-glass/ (NTT America)