On 2014/07/17 11:28 , Randy Bush wrote:
While technically it would be possible to add some feature to the system to do multiple paris variations at (or close to) the same time, this would add a lot of complications to the code base and to result parsing (which is already not simple). Instead, it is already possible to schedule multiple measurements to run at roughly the same time, which provides an approximation to what you describe here.
how close an approximation? chasing ecmp and lag is bad enough without other changes. folk need reproducible results.
As far as I know, the actual hashing algorithms used by load balancers are in general not known. So the only thing paris-traceroute can do is to try to provide consistent results for each variation and try to create enough difference between variations that it likely that all paths are tried. In this context, it doesn't really matter if you try different variations in one measurement or run different measurements. In both cases some bits will be different. But it not possible to predict in advance what is going to happen. Worth pointing out in this context (and it is also documented somewhere) is that if a probe reboots, the bits it uses for paris-traceroute are likely to be different. So consistent results with a single measurement are only achieved for as long as a probe doesn't reboot. Philip