[tor-bugs] Re: #1294 [Tor-Tor server]: Bandwidth weights absent when D=0

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#1294: Bandwidth weights absent when D=0
-----------------------------+----------------------------------------------
  Reporter:  mikeperry       |       Owner:  mikeperry
      Type:  defect          |      Status:  new      
  Priority:  minor           |   Milestone:           
 Component:  Tor-Tor server  |     Version:  0.2.1.22 
Resolution:  None            |    Keywords:           
-----------------------------+----------------------------------------------

Old description:

> When the directory authorites vote that there are insufficient Exit nodes
> for them to be labled as both Exit and
> Guard, the authorities fail to add a bandwidth-weights line in consensus
> method 9. This has two problems:
>
> 1. We could actually create weights in may cases when this does happen.
>
> 2. This decision is made on the individual consensus *votes*, not the
> final consensus. There have been several
> situations so far when the authorites voted not to have Guard+Exit even
> though there was sufficient exit bandwidth
> in the consensus, and vice-versa.
>
> The problem is that this check probably is a good idea to perform,
> because of the large numbers of existing clients that
> we want to avoid using Exits-as-Guards with until they update to the new
> weighting system.
>
> The correct solution should be to tweak the Guard flag such that it
> produces a fixed amount of Guard-flagged nodes in
> the actual consensus. We should allow the weights themselves to handle
> what to do with Guard+Exit nodes.
>
> However, because this is a mostly harmless result that just causes
> clients to revert to the old weights when it
> happens, and because a bit of work and thought is needed to decide how to
> properly allocate the Guard flag, we're
> not going to just do a quick fix and allow weights for the D=0 situation.
> We should fix this issue once we feel
> that enough clients have upgraded to 0.2.2.x for it to make sense to fix
> it properly.
>
> [Automatically added by flyspray2trac: Operating System: All]

New description:

 When the directory authorites vote that there are insufficient Exit nodes
 for them to be labled as both Exit and
 Guard, the authorities fail to add a bandwidth-weights line in consensus
 method 9. This has two problems:

 1. We could actually create weights in may cases when this does happen.

 2. This decision is made on the individual consensus *votes*, not the
 final consensus. There have been several
 situations so far when the authorites voted not to have Guard+Exit even
 though there was sufficient exit bandwidth
 in the consensus, and vice-versa.

 The problem is that this check probably is a good idea to perform, because
 of the large numbers of existing clients that
 we want to avoid using Exits-as-Guards with until they update to the new
 weighting system.

 The correct solution should be to tweak the Guard flag such that it
 produces a fixed amount of Guard-flagged nodes in
 the actual consensus. We should allow the weights themselves to handle
 what to do with Guard+Exit nodes.

 However, because this is a mostly harmless result that just causes clients
 to revert to the old weights when it
 happens, and because a bit of work and thought is needed to decide how to
 properly allocate the Guard flag, we're
 not going to just do a quick fix and allow weights for the D=0 situation.
 We should fix this issue once we feel
 that enough clients have upgraded to 0.2.2.x for it to make sense to fix
 it properly.

 [Automatically added by flyspray2trac: Operating System: All]

--

Comment(by mikeperry):

 See also bugs #1206, #1115, and #1117, which suggest that maybe we should
 just fix the WFU+MTBF code to always give us enough guards, and let the
 balancing algorithms decide what to do with Exit flagged guards.

 The reason this decision should be done in the consensus is that the
 consensus weights are based on the actual final consensus. The decision to
 not vote for Exits as Guards is currently being done with incomplete
 information in the individual authority votes.

-- 
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/1294#comment:1>
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