Re: [tor-bugs] #26805 [Core Tor/Tor]: Work out why Tor networks with all-zero bandwidths are unstable

[Tor Bug Tracker & Wiki]

#26805: Work out why Tor networks with all-zero bandwidths are unstable
--+--
 Reporter:  teor  |  Owner:  (none)
 Type:  defect| Status:  new
 Priority:  Medium|  Milestone:  Tor: unspecified
Component:  Core Tor/Tor  |Version:
 Severity:  Normal| Resolution:
 Keywords:  tor-bwauth|  Actual Points:
Parent ID:  #26803| Points:
 Reviewer:|Sponsor:
--+--

Comment (by teor):

 Replying to [comment:2 neel]:
 > Does "bandwidth" mean consensus weight? Is so, I believe all-zero
 bandwidth networks are unstable because it's hard for a client to
 distinguish the network between different relays as no fraction of a
 relay's bandwidth can be made. Keep in mind that I'm not an expert on Tor
 design and this could be completely inaccurate.

 Yes, clients have trouble when the total is zero, because they try
 dividing by zero  (or similar).
 And clients also have trouble when a relay they need is weighted at zero.

 > I think the solution is that if there's a bandwidth of 0, we
 automatically make it 1 either on the client or on the consensus. I
 haven't looked fully into a solution so this may be an imperfect one.

 That's one solution.

 arma suggested that we fix all the little specific bugs that cause these
 issues, which is a good idea. We should also add unit tests with zero
 bandwidths so they don't happen again.

 I also suggest that we decide what a zero consensus weight means:
 * if it means "never use this relay", we could drop zero-bandwidth relays
 from the consensus
 * if it means "try not to use this relay", we could:
   * act as if zero-bandwidth relays have a very small bandwidth, like 1
   * avoid using the relay in our first pass, and only choose it if we
 can't find any other relays (like we do with the existing ExitNodes option
 when StrictNodes is 0)

 I think that zero consensus weights generally happen when relays are slow
 or unmeasured, so "try not to use this relay" seems like a good response.
 (And a better response for test networks, too.)

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Re: [tor-bugs] #26805 [Core Tor/Tor]: Work out why Tor networks with all-zero bandwidths are unstable

[Tor Bug Tracker & Wiki]

#26805: Work out why Tor networks with all-zero bandwidths are unstable
--+--
 Reporter:  teor  |  Owner:  (none)
 Type:  defect| Status:  new
 Priority:  Medium|  Milestone:  Tor: unspecified
Component:  Core Tor/Tor  |Version:
 Severity:  Normal| Resolution:
 Keywords:  tor-bwauth|  Actual Points:
Parent ID:  #26803| Points:
 Reviewer:|Sponsor:
--+--
Changes (by neel):

 * cc: neel@… (added)


Comment:

 Does "bandwidth" mean consensus weight? Is so, I believe all-zero
 bandwidth networks are unstable because it's hard for a client to
 distinguish the network between different relays as no fraction of a
 relay's bandwidth can be made. Keep in mind that I'm not an expert on Tor
 design and this could be completely inaccurate.

 I think the solution is that if there's a bandwidth of 0, we automatically
 make it 1 either on the client or on the consensus. I haven't looked fully
 into a solution so this may be an imperfect one.

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Re: [tor-bugs] #26805 [Core Tor/Tor]: Work out why Tor networks with all-zero bandwidths are unstable

[Tor Bug Tracker & Wiki]

#26805: Work out why Tor networks with all-zero bandwidths are unstable
--+--
 Reporter:  teor  |  Owner:  (none)
 Type:  defect| Status:  new
 Priority:  Medium|  Milestone:  Tor: unspecified
Component:  Core Tor/Tor  |Version:
 Severity:  Normal| Resolution:
 Keywords:  tor-bwauth|  Actual Points:
Parent ID:  #26803| Points:
 Reviewer:|Sponsor:
--+--

Comment (by arma):

 I would be a fan of "figure out what the issue is", rather than applying
 the bandaid options without knowing whether they actually fix it.

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[tor-bugs] #26805 [Core Tor/Tor]: Work out why Tor networks with all-zero bandwidths are unstable

[Tor Bug Tracker & Wiki]

#26805: Work out why Tor networks with all-zero bandwidths are unstable
--+--
 Reporter:  teor  |  Owner:  (none)
 Type:  defect| Status:  new
 Priority:  Medium|  Milestone:  Tor: unspecified
Component:  Core Tor/Tor  |Version:
 Severity:  Normal|   Keywords:  tor-bwauth
Actual Points:|  Parent ID:  #26803
   Points:|   Reviewer:
  Sponsor:|
--+--
 When I run a chutney network with an empty bwfile, the network seems to
 fail more often.

 We should either:
 * fix this bug on tor clients, or
 * make authorities never vote zero bandwidths:
   * make the minimum bandwidth 1, or
   * drop relays with zero bandwidths from the consensus.

 This blocks adding a bwfile test to make test-network-all in #26803

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