[tor-bugs] #23278 [Core Tor/Tor]: Give user option to use non-Exit Guards only

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#23278: Give user option to use non-Exit Guards only
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 Reporter:  cypherpunks   |          Owner:  (none)
     Type:  enhancement   |         Status:  new
 Priority:  Medium        |      Milestone:
Component:  Core Tor/Tor  |        Version:
 Severity:  Normal        |     Resolution:
 Keywords:                |  Actual Points:
Parent ID:                |         Points:
 Reviewer:                |        Sponsor:
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Comment (by cypherpunks):

 > Specifically, right now Exit capacity is scarce in the network, so every
 relay that has both the Guard flag and the Exit flag is always avoided
 when clients are picking a guard, since they know to leave its bandwidth
 available for people who are using it as an exit.

 More specifically, it depends bandwidth-weights generated by DirAuths for
 consensus document. bandwidth-weights are dynamic depends network's
 weather.

 Simplified code to compute Guard bandwidth by client for Exit+Guard case:
 {{{
 Wd = networkstatus_get_bw_weight(NULL, "Wgd", -1);
 Wdb = networkstatus_get_bw_weight(NULL, "Wdb", -1);
 //Today: Wdb=10000 Wgd=0
 weight = (is_dir ? Wdb*Wd : Wd); // 0 or 0 for today
 final_weight = weight*this_bw; //  0 for WEIGHT_FOR_GUARD
 bandwidths[node_sl_idx] = final_weight + 0.5;
 }}}

 0.5 is not zero after all. It is today, not yesterday or tomorrow.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/23278#comment:6>
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