Multicast routing consists of several protocols forming a complex
system. Success of the multicast infrastructure relies on managing
multicast networks efficiently and monitoring the operation of
these protocols. However, several of these protocols work on an
inter-domain scale and are not particularly stable. Monitoring
from a single location is not effective for troubleshooting
purposes or for gauging the extent of deployment. Consequently,
global monitoring of the multicast infrastructure has become a
necessity because its results are infrastructurewide and are
based on the multiple snapshots collected from different
locations. In this paper we describe the motivation, challenges,
and requirements for a global multicast monitoring system. We
give a brief overview of our monitoring system, called Mantra,
that supports global monitoring. We also present results based on
the analysis of data collected by Mantra from various important
locations in the Internet multicast topology. Our final
conclusion, and not one that can be drawn by looking at any
individual router, is that multicast has a significant amount of
inconsistency in what should be consistent global state.
