scamper

Like its predecessor skitter, scamper is a tool that actively probes the Internet in order to analyze topology and performance. Unlike skitter, scamper supports both IPv6 and IPv4 path probing. It can also discover the maximum transmission unit (MTU) of a given path. Eventual deployment of scamper monitors will extend CAIDA's Macroscopic Topology Project to cover the growing IPv6 topology.

| goals architecture source code |

scamper Goals

characterize macroscopic connectivity and performance of the Internet
identify low frequency persistent routing changes
provide input for building the directed graph from a source to a wide sample of the Internet
track the growth and progress of IPv6 deployment worldwide

scamper Features

The scamper tool captures forward IP paths and round trip time values (RTTs) from a scamper host to a specified list of destinations. When fully deployed, it will continuously send probe packets to destinations in its target list using high-numbered (unused) UDP ports or, alternatively, ICMP echo packets. The list of IP destinations can be a mixture of IPv6 and IPv4 addresses. The number of times each destination is probed per day depends primarily on the total number of destinations in the target list and on the probing options set. It depends to a lesser extent on the current global conditions of the network.

Measure Forward IPv6 Paths
scamper records an IPv6 address seen at each hop from a source to a destination by incrementing the "hop limit" (HLIM) of each IPv6 packet header, and recording replies from each router leading to the destination host.
Measure Forward IPv4 Paths
scamper records an IPv4 address seen at each hop from a source to a destination by incrementing the "time to live" (TTL) of each IPv4 packet header, and recording replies from each router leading to the destination host.
Skip Unresponsive Routers
If a certain router in the path does not reply to scamper probe packets, scamper will send a specified number of probes to this router (default is 2) and then try to probe the next router in the path. It will abandon the whole path if there is more than a specified number of unresponsive hops in a row (default is 5) and the destination itself is unresponsive.
Measure Round Trip Times
scamper can collect round trip time measured to each intermediate router as well as to the destination host.
Measure Path MTU
scamper can measure the path MTU and identify tunnels and MTU bottlenecks from a source to many destinations, using RFC 1191 Path MTU discovery. scamper can also determine the MTU of a link where a router does not send an ICMP fragmentation required message.

Current Status

The WIDE project funded Matthew Luckie from the University of Waikato to further develop scamper and release the source code. The period of funding was for the 1 April 2004 to 31 March 2005. The source code is freely available.

scamper was used to collect data for an IPv6 AS core poster. The poster, and the details on how we collected the data is made available.

The goal of the one-year WIDE funded project was to conduct large scale IPv6 topology measurement using scamper, and to identify technical and operational issues in its measurement.

The plan for the twelve months ending 1 April 2005 involved:

Development of an open source topology probe tool.
- skitter-compatible output format ("warts" files)
- PMTU functionality
- performance optimization
- scamper library functions to read the existing skitter arts files
- updated skcollect and skserver using the new scamper library
Large scale IPv6 topology measurement using scamper
Analysis of the obtained data (co-funded with another source)

About scamper measurement traffic

If you are receiving 32-byte UDP IPv4 probe packets or 52 byte UDP IPv6 probe packets to high numbered ports from an address belonging to one of our current monitors, they are from scamper (assuming they're not from someone spoofing the source address). We are grateful for sites that are receptive to scamper measurements at low frequency. CAIDA's measurement efforts are intended to help users, providers and researchers understand the complexities in the current and future Internet. Analysis of scamper data will provide the community with insight into the complexity of a large, heterogeneous, and dynamic worldwide Internet topology.

If you are receiving scamper measurement traffic and would like measurements to be discontinued to your site, please send mail to scamper-ops@caida.org. We will discontinue measurements to your site. However, please include the IP addresses of the hosts that you wish to have removed from the scamper database. Note that if your site is not measured, it will not show up in any of the analysis results, graphs, or visualizations.