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Multicasting has an increasing importancefor network applications such as groupware or videoconferencing. Several multicast routing protocols have been defined. However they cannot be used directly in the Internet since most inter-domain routers do no implement multicasting. Thus these protocols are mainly tested either on a small scale inside a domain, or through the Mbon~, whose topology is not really the same as Internet topology. The purpose of this paper is to construct a graph using actual routes of the Internet, and then to use this graph to compare some parameters -delays, scaling in term of state or traffic concentration -of multicast routing trees constructed by different algorithms -source shortest path trees and shared trees.

Operators have deployed Multiprotocol Label Switching (MPLS) in the Internet for over a decade. However, its impact on Internet topology measurements is not well known, and it is possible for some MPLS configurations to lead to false router-level links in maps derived from traceroute data. In this paper, we introduce a measurement-based classification of MPLS tunnels, identifying tunnels where IP hops are revealed but not explicitly tagged as label switching routers, as well as tunnels that obscure the underlying path. Using a large-scale dataset we collected, we show that paths frequently cross MPLS tunnels in today's Internet: in our data, at least 30% of the paths we tested traverse an MPLS tunnel. We also propose and evaluate several methods to reveal MPLS tunnels that are not explicitly flagged as such: we discover that their fraction is significant (up to half the explicit tunnel quantity) but most of them do not obscure IP-level topology discovery.

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