A Looking Glass is a piece of software running as a CGI on an ISP's webserver that allows external users to get a look at routing and network behavior within their network. The software is usually a Perl script that resides in the CGI bin of a web server. The script executes shell commands, accesses a remote router, performes either a ping, trace, or one of several show commands allowing a view of the IP and BGP route tables. The CGI then returns the information as a web page.

Looking Glasses are most commonly used for verifying routing between providers, and for verifying that routes are propagating correctly across the Internet.

Choose your looking glass carefully as many web-based looking glasses are provided by an ISP who serves a specific geographic region. Organizations using BGP should choose a looking glass that is their own ISP or an upstream ISP.

Public Looking Glasses

CAIDA maintains a search tool for finding traceroute and looking glass servers


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