[tor-talk] understanding metrics bw graphs

[Karsten Loesing]

On 31/07/14 23:44, Nusenu wrote:
> Hi,
> 
> I would have a question regarding the bw-flags graphs on metrics.tpo [1]
> 
> "guard bw history"
> a) Does this include the entire accumulated traffic of relays having
> the guard flag? (which would include the traffic of a guard relay
> acting as a middle or exit relay - if it also has the exit flag)
> 
> or
> 
> b) Does this only and exclusively include the entire accumulated
> traffic that *enters* the tor network via all guard relays?
> (to actually do that the traffic accounting on relays would have to do
> accounting accordingly on a per connection type level)

a) is correct.

Minor nitpick: a relay can exit even if it doesn't have the Exit flag;
that flag is only assigned for load-balancing purposes.

There's no data available for b).

> Which would bring me to the next question (which would be required to
> actually do the required accounting for (b)): Is a relay able to tell
> whether it is being used as first or second hop solely by looking at
> packets (not their source)?

Looking at the packet source and comparing it to the list of known
relays would probably be the most reliable way for counting bytes as
first or second hop.  But this is not implemented, and there are plans
to implement this, to the best of my knowledge.

> Same question applies to: "exit bw history"

a).

> Does your answer also apply to [2]?

Yes, except that [2] distinguishes between Guard only and Guard & Exit.

All the best,
Karsten

> [1] https://metrics.torproject.org/bandwidth.html#bandwidth-flags
> 
> [2] https://metrics.torproject.org/bandwidth.html#bwhist-flags