Filename: 138-remove-down-routers-from-consensus.txt
Title: Remove routers that are not Running from consensus documents
Author: Peter Palfrader
Created: 11-Jun-2008
Status: Closed
Implemented-In: 0.2.1.2-alpha
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 1/4 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 therefore never be used by clients who use this consensus.
Not listing those routers will save 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.