[tor-bugs] #17773 [Core Tor/Tor]: Should clients avoid using guards that lost the Guard flag?

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#17773: Should clients avoid using guards that lost the Guard flag?
-------------------------------+------------------------------
 Reporter:  arma               |          Owner:  arma
     Type:  enhancement        |         Status:  accepted
 Priority:  Medium             |      Milestone:  Tor: 0.2.???
Component:  Core Tor/Tor       |        Version:
 Severity:  Normal             |     Resolution:
 Keywords:  TorCoreTeam201606  |  Actual Points:
Parent ID:                     |         Points:  medium?
 Reviewer:                     |        Sponsor:  None
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Comment (by asn):

 Are we sure that we keep on connecting to nodes that used to be guards but
 are not anymore?

 If you check `entry_guard_set_status()` which gets called by
 `entry_guards_compute_status()` everytime we receive a new consensus, you
 can see:
 {{{
   else if (!options->UseBridges && !node->is_possible_guard &&
            !routerset_contains_node(options->EntryNodes,node))
     *reason = "not recommended as a guard";
 }}}
 which will later make the `entry_guard_t` get marked with `bad_since`.
 Then we will stop picking it as guard.

 To be honest, I'm not sure what's the best behavior here. Both choices
 (are there only two?) seem to have positives and negatives. FWIW, I'm
 pretty sure that the (incomplete) prop259 specifies the same behavior as
 the current code (mark nodes as bad and don't connect to them when they
 are not guards anymore)

--
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/17773#comment:13>
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