Tor design proposals

Filename: 185-dir-without-dirport.txt
Title: Directory caches without DirPort
Author: Nick Mathewson
Created: 20-Sep-2011
Status: Superseded
Superseded-by: 237

Overview:

  Exposing a directory port is no longer necessary for running as a
  directory cache.  This proposal suggests that we eliminate that
  requirement, and describes how.

Motivation:

  Now that we tunnel directory connections by default, it is no
  longer necessary to have a DirPort to be a directory cache.  In
  fact, bridges act as directory caches but do not actually have a
  DirPort exposed.  It would be nice and tidy to expand that
  property to the rest of the network.

Configuration:

  Add a new torrc option, "DirCache".  Its values can be "0", "1",
  and "auto".  If it is 0, we never act as a directory cache, even
  if DirPort is set.  If it is 1, then we act as a directory cache
  according to same rules as those used for nodes that set a
  DirPort.  If it is "auto", then Tor decides whether to act as a
  directory cache based on some future intelligent algorithm. "Auto"
  should be the new default.

Advertising cache status:

  Nodes that are running as a directory cache should set the entry
  "dir-cache 1" in their router descriptors.  If they do not have a
  DirPort set, or do not have a working DirPort, they should give
  their directory port as 0 in their router lines.  (Nodes that have
  a working directory port advertise it as usual, and also include a
  "dir-cache" line.  Nodes that do not serve directory information
  should set their directory port to 0, and not include any
  dir-cache line.  Implementations should accept and ignore
  dir-cache lines with values other than "dir-cache 1".)

Consensus:

  Authorities should assign a "DirCache" flag to all nodes running
  as a directory cache.

  This does not require a new version of the consensus algorithm.