Re: Clone nodes

[Paul Syverson <syverson@xxxxxxxxxxxxxxxx>]

On Wed, Sep 26, 2007 at 01:50:08AM -0400, Roger Dingledine wrote:
> On Wed, Sep 26, 2007 at 01:27:57AM -0400, Gregory Maxwell wrote:
> > 
> > I've configured this on a private testing tor network and it appears
> > to work without problems, but it is a huge pain to build a fake tor
> > network big enough to do real testing.  I don't want to connect my
> > clone nodes to the public network if there is a risk of causing
> > breakage. ;)
> 
> I don't think it would be catastrophic if you want to do it for testing.
> 
> In fact, once upon a time, we had a feature called "router twins"
> that is exactly what you describe.  We were hoping it would provide
> better robustness for a given server -- this was back in the day when we
> were using actual onions to lay circuits, and envisioning actual reply
> onions rather than the current rendezvous design, so there was a need
> for servers to be around for hours or even days after you built an onion.
> 

Minor historic quibble: Router twins did start in the day of onions to
lay circuits, but they lived at least for a while into the onion skin
(incremental path) era. More importantly, they weren't just for
replies: there were multiple motivations, e.g., network and client
overhead. You didn't need to rebuild a path from scratch if a node on
the path was down (you could go to the twin). Note that you could do
this with telescoping by just going to another node (with another
onion key), but (1) it would still involve additional exchanges and
exponentiations, so savings wouldn't be as great (2) it's a bad idea
from an anonymity perspective (which is the main reason why such
circuit building was quickly abandoned from the code once twins were
gone). Load balancing for both network performance/overhead and for
anonymity were also considerations. In the end we didn't have time to
properly figure out the tradeoff implications of twins so left it as
something to possibly consider again in the future in our copious free
time.

aloha,
Paul