Re: Greetings/Question - Was: RE: Have some consideration for users...

[Roger Dingledine <arma@xxxxxxx>]

On Fri, Sep 02, 2005 at 09:08:27PM -0400, Jeffrey F. Bloss wrote:
> What IS the impact on the tor network if a node suddenly drops off the
> face of the planet, or appears and disappears every half hour or so
> for an 8 hour span? I'd assume since tor is "real time" the node is
> simply routed around, correct? How fast are these things compensated
> for?

Tor servers publish an "uptime" in their server descriptor, which is
the time they've been available/working at their current IP.

If servers die suddenly, Tor circuits that use them are broken. If
somebody is using one of those circuits (e.g. for his irc connection),
then it gets cut.

Tor clients have a config option "LongLivedPorts" which defaults to
"21,22,706,1863,5050,5190,5222,5223,6667,8300,8888". If a socks request
asks for one of these ports, then it uses a circuit constructed entirely
of nodes with uptimes of at least a day. The theory is that if they've
been up that long, they'll probably be up a while longer.

So for things like port 80 where the request is typically quite quick,
a flaky node is fine, since it's either up during the request or it's not
(in which case we'll keep building circuits until we get one that works).

The answer to your question is "If your node is always like this, then
it's probably not worth while to run a Tor node. But if it's fine for
most days and it has this behavior one afternoon a week, then it's useful
to have it."

Hope that helps,
--Roger