[tor-bugs] #15516 [Core Tor/Tor]: Consider rate-limiting INTRODUCE2 cells when under load

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#15516: Consider rate-limiting INTRODUCE2 cells when under load
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 Reporter:  special                              |          Owner:  (none)
     Type:  enhancement                          |         Status:  new
 Priority:  Medium                               |      Milestone:  Tor:
                                                 |  unspecified
Component:  Core Tor/Tor                         |        Version:
 Severity:  Normal                               |     Resolution:
 Keywords:  SponsorU-deferred, tor-dos, tor-hs,  |  Actual Points:
  network-team-roadmap-2019-Q1Q2                 |
Parent ID:  #29999                               |         Points:  10
 Reviewer:                                       |        Sponsor:
                                                 |  Sponsor27-can
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Comment (by arma):

 Another idea I was considering here, but ultimately abandoned as more
 complex than we need, was to somehow timestamp the intro1 cell when it
 gets received at the intro point, which would allow the onion service to
 examine how many seconds have passed and discard it if it's more than n
 seconds ago. That would essentially mean that we have n *seconds* of valid
 intro2 cells in flight, rather than at-most-n *circwindows* of intro2
 cells in flight. This approach would handle congestion that happens inside
 the network (between the intro point and the service), in that if it takes
 a long time for the intro2 cell to make it from the intro point to the
 onion service, it's less likely that the client is still around and
 waiting for the connect-back.

 But how exactly to do the timestamp, and how and whether we need to
 synchronize clocks, made this too klunky an idea.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/15516#comment:29>
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