02-12-2016, 01:04 AM
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Account Shutdown
Industry Role:
Join Date: Oct 2008
Location: Gone
Posts: 3,611
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Meh, looks like a new relay is initially boring: The lifecycle of a new relay | The Tor Blog
Quote:
Phase one: unmeasured (days 0-3).
When your relay first starts, it does a bandwidth self-test: it builds four circuits into the Tor network and back to itself, and then sends 125KB over each circuit. This step bootstraps Tor's passive bandwidth measurement system, which estimates your bandwidth as the largest burst you've done over a 10 second period. So if all goes well, your first self-measurement is 4*125K/10 = 50KB/s. Your relay publishes this number in your relay descriptor.
The directory authorities list your relay in the network consensus, and clients get good performance (and balance load across the network) by choosing relays proportional to the bandwidth number listed in the consensus.
Originally, the directory authorities would just use whatever bandwidth estimate you claimed in your relay descriptor. As you can imagine, that approach made it cheap for even a small adversary to attract a lot of traffic by simply lying. In 2009, Mike Perry deployed the "bandwidth authority" scripts, where a group of fast computers around the Internet (called bwauths) do active measurements of each relay, and the directory authorities adjust the consensus bandwidth up or down depending on how the relay compares to other relays that advertise similar speeds. (Technically, we call the consensus number a "weight" rather than a bandwidth, since it's all about how your relay's number compares to the other numbers, and once we start adjusting them they aren't really bandwidths anymore.)
The bwauth approach isn't ungameable, but it's a lot better than the old design. Earlier this year we plugged another vulnerability by capping your consensus weight to 20KB until a threshold of bwauths have an opinion about your relay â?? otherwise there was a several-day window where we would use your claimed value because we didn't have anything better to use.
So that's phase one: your new relay gets basically no use for the first few days of its life because of the low 20KB cap, while it waits for a threshold of bwauths to measure it.
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