Proposal: remove down routers from consensus

[Geoffrey Goodell]

Suggest that instead of removing routers that are not running, we simply
remove routers for which we do not have descriptors in dir/server/all.
Does this make sense?

Geoff

On Thu, Jun 12, 2008 at 10:28:41PM +0200, Peter Palfrader wrote:
> This is a pretty low hanging fruit and part of the job to make tor
> bootstrap faster even if your bandwidth is really small.
> 
> 
> Filename: xxx-remove-down-routers-from-consensus
> Title: Remove routers that are not Running from consensus documents
> Version: $Revision$
> Last-Modified: $Date$
> Author: Peter Palfrader
> Created: 11-Jun-2008
> Status: Open
> 
> 1. Overview.
> 
>   Tor directory authorities hourly vote and agree on a consensus document
>   which lists all the routers on the network together with some of their
>   basic properties, like if a router is an exit node, whether it is
>   stable or whether it is a version 2 directory mirror.
> 
>   One of the properties given with each router is the 'Running' flag.
>   Clients do not use routers that are not listed as running.
> 
>   This proposal suggests that routers without the Running flag are not
>   listed at all.
> 
> 2. Current status
> 
>   At a typical bootstrap a client downloads a 140KB consensus, about
>   10KB of certificates to verify that consensus, and about 1.6MB of
>   server descriptors, about half of which it requires before it will
>   start building circuits.
> 
>   Another proposal deals with how to get that huge 1.6MB fraction to
>   effectively zero (by downloading only individual descriptors, on
>   demand).  Should that get successfully implemented that will leave the
>   140KB compressed consensus as a large fraction of what a client needs
>   to get in order to work.
> 
>   About one third of the routers listed in a consensus are not running
>   and will therefor never be used by clients who use this consensus.
>   Not listing those routers will safe about 30% to 40% in size.
> 
> 3. Proposed change
> 
>   Authority directory servers produce vote documents that include all
>   the servers they know about, running or not, like they currently
>   do.  In addition these vote documents also state that the authority
>   supports a new consensus forming method (method number 4).
> 
>   If more than two thirds of votes that an authority has received claim
>   they support method 4 then this new method will be used:  The
>   consensus document is formed like before but a new last step removes
>   all routers from the listing that are not marked as Running.
> 
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