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Weekly report

25

Mar

2014

Research has been carried out into the possibility that some load balancers partition packets to their successor nodes based on packet fields other than those that are considered usual. Thirteen fields where chosen for the test and scamper, the program we use for traceroute MDA, was modified to carry them out. Traceroute MDA is an analysis that scans the Internet for load balancers and other network topology information.

Small numbers of load balancers have been found that do this, and many of the same load balancers are found by different field tests. The next question was to find out if these load balancers behaved as load balancers all the time. The case of also being a per packet load balancer was excluded from the counts i.e one that partitions randomly. Three cases emerged that of a small number of hits and misses, a large number of misses and a small number of hits and no hits. A miss means that no load balancer was found though the same node that was a load balancer in another trace exists in the topology, but with only one successor if any. There may be some more special cases to exclude from the data such as the node being last in the trace etc. It appears that some of these load balancers show fairly consistent load balancing across a couple of field types, others show the load balancing behaviour only rarely.

The Internet simulator simulates doubletree and traceroute in its unmodified state. Traceroute determines Internet topology between a source and destination, but not including load balancers. Doubletree is a modified version of traceroute that is designed to avoid repeatedly analysing the same parts of the Internet, by sharing information between vantage points.

We are currently trying to simulate unmodified doubletree using very large datasets. This caused the simulator to run a long time. Analysis with valgrind callgrind indicates that the gang analysis case which is being used is the major problem here. So, the question is now being asked: can we do without gang analysis for this work?

A fast mapping like protocol has been set up for detecting black holes in load balancers. It involves one round of traceroute MDA analysis followed by eight rounds of Paris traceroute, followed by one further round of MDA. Paris traceroute causes the same path through a load balancer to be consistently followed. Comparing the initial and final MDA traces determines if a change in topology has occurred in the Internet. If this is the case finding a short Paris trace may not be due to a blackhole. After excluding all of the special cases that I can think of there remain some cases which appear to be blackholes in load balancers in our data.

In order to run this type of analysis on PlanetLab we prefer to use ICMP packets. Modifications were made to scamper on Yoyo our University computer outside the firewall, to randomly choose a flow ID for each trace and a run was initiated.

It has been decided that regression equations may not be sufficiently fundamental to understand the mathematical models predictions. In the first instance I am extracting 'proportional to' type relationships from these equations to see if more fundamental inferences may be made about the structure of the model.

It will also be desirable to try and derive these proportional to relationships from theoretical arguments. For example, is the number of packets sent from a vantage point proportional to the number of destinations probed in system where there are no savings measures taken. If a match or resolution is found between these two approaches then that would be good progress.

It may also be necessary to focus on the data sets with a large packet limit and determine if incomplete load balancer information should be counted if it seems sensible to do so. This is important because a small number of very high cost load balancers may exist, and these are the most important ones to avoid repeated analysis of.