Harsha V. Madhyastha
Vijay Kumar Adhikari
Peter van Wesep
Traceroute is the most widely used Internet diagnos-
tic tool today. Network operators use it to help identify
routing failures, poor performance, and router misconﬁg-
urations. Researchers use it to map the Internet, predict
performance, geolocate routers, and classify the perfor-
mance of ISPs. However, traceroute has a fundamental
limitation that affects all these applications: it does not
provide reverse path information. Although various pub-
lic traceroute servers across the Internet provide some
visibility, no general method exists for determining a re-
verse path from an arbitrary destination.
In this paper, we address this longstanding limitation
by building a reverse traceroute system. Our system pro-
vides the same information as traceroute, but for the re-
verse path, and it works in the same case as traceroute,
when the user may lack control of the destination. We
use a variety of measurement techniques to incrementally
piece together the path from the destination back to the
source. We deploy our system on PlanetLab and compare
reverse traceroute paths with traceroutes issued from the
destinations. In the median case our tool ﬁnds 87% of
the hops seen in a directly measured traceroute along the
same path, versus only 38% if one simply assumes the
path is symmetric, a common fallback given the lack of
available tools. We then illustrate how we can use our
reverse traceroute system to study previously unmeasur-
able aspects of the Internet: we present a case study of
how a content provider could use our tool to troubleshoot
poor path performance, we uncover more than a thousand
peer-to-peer AS links invisible to current topology map-
ping efforts, and we measure the latency of individual
backbone links with average error under a millisecond.
Traceroute is a simple and widely used Internet diagnos-
tic tool. It measures the sequence of routers from the
source to the destination, supplemented by round-trip de-
lays to each hop. Operators use it to investigate routing
failures and performance problems . Researchers use
it as the basis for Internet maps [1, 22, 34], path predic-
tion , geolocation [42, 14], ISP performance analy-
sis , and anomaly detection [46, 19, 44, 43].
However, traceroute has a fundamental limitation – it
Dept. of Computer Science, Univ. of Washington, Seattle.
Dept. of Computer Science, Univ. of California, San Diego.
Dept. of Computer Science, Univ. of Minnesota.
provides no reverse path information, despite the fact that
policy routing and trafﬁc engineering mean that paths
are generally asymmetric . As Richard Steenbergen,
CTO for nLayer Communications, put it at a recent tuto-
rial for network operators on troubleshooting, “the num-
ber one go-to tool is traceroute,” but “asymmetric paths
[are] the number one plague of traceroute” because “the
reverse path itself is completely invisible” .