[tor-dev] Review of Proposal 212, Increase Acceptable Consensus Age (was: Tor proposal status (December 2013))

Karsten Loesing karsten at torproject.org
Fri Dec 20 17:54:07 UTC 2013

On 12/17/13 10:31 PM, Nick Mathewson wrote:
> 212  Increase Acceptable Consensus Age
>      This proposal suggests that we increase the maximum age of a
>      consensus that clients are willing to use when they can't
>      find a new one, in order to make the network robust for
>      longer against a failure to reach consensus.  In my
>      opinion, we should do that.  If I recall correctly, there
>      was some tor-dev discussion on this one that should get
>      incorporated into a final, implementable version. (11/2013)

Hi Nick,

I agree with the idea that clients should accept an old consensus up to
3 days instead of 1.  It's stressful enough to nag directory authority
operators to look after their machines if they fail to produce a
consensus for a few hours.  I did that a couple of times, and it
stressed me out every single time.  I don't want to imagine how bad such
a situation would be during the holidays or CCC.

You mention a tor-dev discussion above that should get incorporated.  Do
you have a link?  A quick search in my inbox didn't help.

Here's some feedback from reading the proposal:

- Section 6.1 of dir-spec.txt says that "Circuits SHOULD NOT be built
until the client has [...] a live consensus network status", but that
means 3 hours after valid-after, AFAIK.  Should we rather specify here
that clients MAY use a consensus for up to 3 days after its valid-after
time if they don't find a more recent one?  Or is this something to
leave to the implementation and leave open in dir-spec.txt?

- If the new 3 days constant should become part of dir-spec.txt, what
about the suggested time after which old router descriptors may safely
be removed from caches?  (Would you accept patches to dir-spec.txt that
specify related time constants that are currently only written to the code?)

- Do we really plan to raise the 3 days to something higher when the
"proposals related to ticket #7126 [...] are complete and implemented"?
 If so, would it make sense to make the 3 days constant a new consensus
parameter, rather than hard-code it?

- I didn't review the Implementation Notes part in detail, yet.  But it
feels wrong that OLD_ROUTER_DESC_MAX_AGE is now only 3 days 18 hours
when it was 5 days before.

All the best,

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