If you have AS and more then one upstream you can meet strange traffics behavior sometimes. Suddenly you can see that biggest part of you traffic goes from one upstream or familiar pattern of traffics distribution has changed. It happens cause something changes, far away from you and your provider . Maybe one big provider changed connection to another. It is normal work of BGP, but it could be unpleasant and unpredictable.
The analysis of these issues may be difficult. The “BGP play” can help you. This service provides you information about changes of your announces in simple visual view. This servise live here http://bgplay.routeviews.org/.
Both of these services may don`t work through proxy.
This post could be updated if I find some similar service.