Extra alert information for the "prefix acessible to single T1" alert
This alert triggers when a prefix goes from not depending on more than a single tier 1 (or not existing) to depending on a single T1.
Two graphs are displayed to assist in debugging, one with a title that says “Before” that shows what bgp.tools knew about the prefix before it became dependent on a single T1, and a graph of the propergation at the time the alert was processed.
This alert can take some time to fire, as it uses a different data source to most BGP alerts. The date on the top of the graphs should let you know when bgp.tools processed each routing snapshot
Most users should not need this alert, and enabling this alert should be done with consideration if such a situation helpful to be aware of.
You can find a table of what bgp.tools considers tier 1 networks at the bottom of this page