[tor-bugs] #13414 [Tor]: Increase Authorities' AuthDirMaxServersPerAddr to 4 or 8 to use more processors

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#13414: Increase Authorities' AuthDirMaxServersPerAddr to 4 or 8 to use more
processors
------------------------+---------------------------------
     Reporter:  teor    |      Owner:
         Type:  defect  |     Status:  new
     Priority:  normal  |  Milestone:  Tor: 0.2.6.x-final
    Component:  Tor     |    Version:  Tor: unspecified
   Resolution:          |   Keywords:  tor-auth tor-router
Actual Points:          |  Parent ID:
       Points:          |
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Comment (by teor):

 Notes from a discussion on #tor-dev, to be turned into an email to tor-
 relays

 [14:30] <teor> A bit of context: multithreading, optimisation, and / or
 IPv6 will eventually solve this issue
 [14:31] <qwerty1> yeah
 [14:31] <teor> But in the meantime, many routers are limited by IPv4
 scarcity, limited tor parallelism, and increasing cores per server
 [14:31] <teor> Some are also sharing IPv4 addresses inadvertently through
 NAT and/or VPS
 ...
 [14:35] <teor> My quick DoS calculations are: to equal the size of the Tor
 network, currently an attacker needs to control 3000 IPv4 addresses = 12 x
 /24
 ...
 [14:36] <teor> And 8 per IP is 750 IPv4 addresses - 3 x /24
 [14:37] <teor> Any larger than 8, and an attacker with a single /24 can
 have a significant impact on the network. This is clearly undesirable.
 [14:38] <teor> Also, as far as OS resources go, any more than 8 starts to
 hit file and process scheduling hard
 ...
 [14:39] <teor> And hardware: 4-8 is the most common number of logical
 cores for Intel's Xeon range. Others are similar.
 [14:39] <teor> Although AFO-Admin's router may need up to 14 tor processes
 to use all their bandwidth. But that's just 1 more IP at 8 per IP.
 [14:40] <teor> TL;DR: I like 8

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/13414#comment:4>
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