AdNet Telecom, observed February 13th, 2011

LIFEGUARD identified a failure keeping one of its sources, located in China, from reaching a router in Romania. The  historical atlas revealed that the forward path to Romania went through AdNet Telecom, one of the destination's providers, whereas the reverse path left the destination AS through NTT, a different provider.  Using spoofed pings, the system isolated the problem to the forward path. LIFEGUARD then successfully measured the entire (spoofed) reverse traceroute back from the destination, revealing that it still went via NTT. 

The Chinese source's current traceroute followed the historical forward path to AdNet Telecom but terminated at a router in that AS.  This result indicated a failure reaching the destination from AdNet.  Furthermore, some other LIFEGUARD vantage points could reach the destination during the failure, and they all reached it via NTT, supporting the hypothesis.  Other vantage points could reach the destination via NTT, and the source could ping hops in NTT that appeared on the reverse path back to China.  These measurements suggested that if networks behind the failure could switch to paths through NTT, they could effectively avoid the problem with AdNet.