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I'm trying to understand the criteria by which authorities determine their vote for the guard flag in order to elucidate why this flag on my relay is flapping. I see a scattering of information from having a rummage around the 'net, but nothing that appears to describe how the different authorities come to such varied conclusions.

The relay in question runs 0.4.1.9, is assigned and has tested at 3MB/s, and has existed for 31d with a current uptime of 10d. Checking the current consensus of each authority listed in consensus health shows that, during my time as a guard, I have the vote of never more than five of the nine authorities, and during a no guard flag period I have guard votes from anywhere between two and four authorities. Furthermore the listed bwauth relay, moria1, never seems to vote for hsdir or guard flags, though in the case of hsdir all the others have. Anecdotally, moria1 is also running by far the latest version, 0.4.4.0-alpha-dev.

Looking through the directory spec it appears that I fall well within the guard-wfu and guard-tk thresholds of 0.98 and 8 days respectively and I cannot see any other flag-threshold which may apply to guard flag selection. I've been holding off upgrading to tor-0.4.2.7 or tor-0.4.3.5 in order to gain some uptime while I look into this, but it doesn't appear that should be a limitation in the authority vote as it is listed in dir-spec.txt as a recommended version.

Furthermore I don't believe that I have any IP connectivity issues to the authorities which would cause them to have an intermittent view of my node (relay is in AS5089, I've not yet started a deep dive to determine if there's been any BGP shenanigans during this period but basic reachability tests have consistently been ok). I've also carefully investigated and concluded that there's nothing in my firewall which is dropping relevant connections.

Can anyone enlighten me to why the consensuses of the relays would be so different, or even perhaps something else I can look into, given they've had plenty of time to "see" my relay?

Many thanks.

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    Can you post the name or fingerprint of you relay? My guess is that your advertised bandwidth alternates around the 2 MB threshold for authorities that don't take measurements, so sometimes they will vote for the guard flag, and sometimes they will vote against. Your tor version doesn't matter here, it is eligible for the guard flag from all authorities. – Steve May 17 '20 at 18:10
  • Thanks for your reply Steve. I'd prefer not to post that as the relay is on a personal connection, but you are entirely correct; every bwauth which has measured below the 2MB/s threshold has declined the guard flag, and every authority which has measured above 2MB/s has voted for the guard flag. It's good to know that the version is not an issue and that the connection is just on the ragged edge of having the required bandwidth to the more distant authorities. Your response is much appreciated, and if you would like to post this as an answer I would be happy to vote it appropriately. – hygri May 17 '20 at 22:39

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