Applications of the IP Timestamp Option to Internet Measurement
Justine Sherry · 2010
Limited support and inconsistent behavior for IP options has led to the common belief that most options cannot be useful. IP timestamp was no exception, until recently, when prespecified IP timestamp measurements were successfully integrated into the Reverse traceroute system. Prespecified timestamps allow the sender to request a series of up to four timestamps from all routers which may receive the packet. Each machine that receives a timestamp probe checks to see whether the next, unstamped IP address matches its own, and if so, provides a timestamp. In this paper, we provide a more extended argument for the role of prespecified timestamps in the measurement toolkit, and demonstrate two new practical use cases for timestamp measurements. We discover over 47 % of ICMP ping-responsive routers in our sample support timestamp options, and both document and suggest methods for dealing with some of the differences between implementations of the timestamp option. Where supported, timestamp probes can take advantage of several attributes uncharacteristic of other common measurement tools: a view of the complete path the probe takes, combined responses from up to four requested addresses, and timestamp values from each responsive address. Illustrating these characteristics, we provide several use cases for timestamp probes. First, we describe how timestamps are integrated into the Reverse traceroute system, discovering routers on the path taken from a destination back to the requesting source. Next, we confirm IP aliases by combining multiple timestamp requests for candidate alias pairs in the same probe. In our application, we identify thousands of alias clusters currently unaddressable by the leading alias resolution technique. As our final use case, we apply the literal timestamp values to assessing one-way link delay. With this technique, we measure the delay between backbone PoPs on the Internet2 network with values comparable to those discovered through measurements at the source.