Archipelago Monitor Statistics
Archipelago (Ark): CAIDA's active measurement infrastructure serving the network research community since 2007.
Statistical information for the topology traces taken by this individual Ark monitor is displayed below. See the main statistics page for the full list of monitors
Medical Express (RCS/RDS))
AS Path Dispersion (by IP Hop)
Use the following link to download the data used to render this graph in ASCII, comma-separated values format here: (CSV output
This graph tells you more (compared to the AS Dispersion by AS Hop graph)
about where different ASes transit data to their peers. For instance, some
routers within an AS will pass off their packets to many other ASes at
a single IP hop, whereas others will send some packets to different ASes
but continue to move data within their own AS. It is useful to compare these
results with the hosting organization's information about what ASes are
providing transit for your data, to see whether it matches what the Ark
probes have discovered.
It is important to recognize that these graphs are meant to illuminate the
routing from a monitor, and not to show the volume of traffic normally
flowing on the links or their bandwidth. Because of this, an AS/IP that might
only be used for a small amount of actual traffic (but routes to a large
section of the address space) can seem disproportionately large on the
Characteristics of this graph
In this graph, we show the AS-level path dispersion, but adjacent IP hops
within the same AS are not aggregated.
It is characterized by AS chains that seems to break apart as one moves to
the right; often a portion of paths will leave an AS at a certain IP hop
distance and move on to a variety of other ASes, but the rest will remain
within that AS for another hop or two (or ten) before finally exiting that
AS. This lends the graph a step-like quality.
Routed /24 Topology Dataset
for more information. This summary applies
to all the dispersion graphs.)
Ark monitors collect data by sending scamper probes continuously to
destination IP addresses. Destinations are selected randomly from each
routed IPv4 /24 prefix on the Internet such that a random address in each
prefix is probed approximately every 48 hours (one probing cycle).
A single monitor won't probe all prefixes, but the prefixes it does probe
will be randomly distributed, which gives a good sample cross section of
the address space.
As each probe travels from the monitor to its final destination, it passes
through several IP addresses (ie, routers) which are owned by different
autonomous systems (ASes).
How This Graph was Created
(This applies to all the dispersion graphs.)
We first take the IP addresses found in each path and look up its
corresponding AS, creating a set of AS paths.
We use heuristics to infer any unknown
values in the IP and AS paths.
First, any range of unknown ASes whose previous and following hops have the
same value are all assumed to be within the same AS.
10 ?? ?? ?? 10
10 10 10 10 10
If there exists only one other known value between two neighboring values,
the unknown hop is assigned that value. This can often happen when
a router gives inconsistent responses, leaving an unknown hop some times
and returning valid data at other times.
For example, say there are only three paths:
10 20 30 40 50
10 20 30 42 52
10 ?? 30 45 55
From this, we infer the unknown hop in the third path, and end up with:
10 20 30 40 50
10 20 30 42 52
10 20 30 45 55
Then, we merge all the paths together into a tree
structure to show how they disperse from the monitor as they go to
their destinations. Each column is broken into smaller column sections
based on the size of the previous hop.
The Y axis represents the number of probe paths that go through
a particular IP address or AS.
The graph we create is a tree (as opposed to the actual network, where
multiple paths can reconverge after diverging earlier), which allows IPs
and ASes to show up several times within the same column.
Non-grayscale colors are assigned
to the ASes that show up the most, which are typically early in a path.
Less numerous ASes are assigned a dark grey, whereas black is used to
denote hops after the end of a particular path.
Any hops with an
IP or AS are denoted with '??' and
are colored a lighter grey.
This kind of dispersion graph originated as a Skitter
(see section V.C).