[Bitcoin-development] Zero-Conf for Full Node Discovery

Mike Hearn mike at plan99.net
Tue May 26 10:48:46 UTC 2015

Very interesting Matt.

For what it's worth, in future bitcoinj is very likely to bootstrap from
Cartographer nodes (signed HTTP) rather than DNS, and we're also steadily
working towards Tor by default. So this approach will probably stop working
at some point. As breaking PorcFest would kind of suck, we might want a
ZeroConf/Rendezvous solution in place so local LANs can capture Bitcoin
traffic away from Tor (with some notification to the user, presumably).

On Tue, May 26, 2015 at 7:47 AM, Matt Whitlock <bip at mattwhitlock.name>

> On Tuesday, 26 May 2015, at 1:15 am, Peter Todd wrote:
> > On Tue, May 26, 2015 at 12:52:07AM -0400, Matt Whitlock wrote:
> > > On Monday, 25 May 2015, at 11:48 pm, Jim Phillips wrote:
> > > > Do any wallets actually do this yet?
> > >
> > > Not that I know of, but they do seed their address database via DNS,
> which you can poison if you control the LAN's DNS resolver. I did this for
> a Bitcoin-only Wi-Fi network I operated at a remote festival. We had well
> over a hundred lightweight wallets, all trying to connect to the Bitcoin
> P2P network over a very bandwidth-constrained Internet link, so I poisoned
> the DNS and rejected all outbound connection attempts on port 8333, to
> force all the wallets to connect to a single local full node, which had
> connectivity to a single remote node over the Internet. Thus, all the
> lightweight wallets at the festival had Bitcoin network connectivity, but
> we only needed to backhaul the Bitcoin network's transaction traffic once.
> >
> > Interesting!
> >
> > What festival was this?
> The Porcupine Freedom Festival ("PorcFest") in New Hampshire last summer.
> I strongly suspect that it's the largest gathering of Bitcoin users at any
> event that is not specifically Bitcoin-themed. There's a lot of overlap
> between the Bitcoin and liberty communities. PorcFest draws somewhere
> around 1000-2000 attendees, a solid quarter of whom have Bitcoin wallets on
> their mobile devices.
> The backhaul was a 3G cellular Internet connection, and the local Bitcoin
> node and network router were hosted on a Raspberry Pi with some Netfilter
> tricks to restrict connectivity. The net result was that all Bitcoin nodes
> (lightweight and heavyweight) on the local Wi-Fi network were unable to
> connect to any Bitcoin nodes except for the local node, which they
> discovered via DNS. I also had provisions in place to allow outbound
> connectivity to the API servers for Mycelium, Blockchain, and Coinbase
> wallets, by feeding the DNS resolver's results in real-time into a
> whitelisting Netfilter rule utilizing IP Sets.
> For your amusement, here's the graphic for the banner that I had made to
> advertise the network at the festival (*chuckle*):
> http://www.mattwhitlock.com/bitcoin_wifi.png
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