Standards (was [BitTorrent] Back to Merkle Hash Trees...)

Justin Cormack justin at
Mon Feb 7 19:32:16 EST 2005

> >From: Brian Dessent <brian at>
> > Olaf van der Spek wrote:
> > 
> > > > Yeah, that'd work.  But the other issues surrounding ipv6 have been
> > > > hashed out over and over on this list in the past so there's more than
> > > > just adapting the binary peers list in the tracker response.  (as I'm
> > > > sure you're aware of...)
> > > 
> > > I know, I know, but I was wondering about the 'The fact is it's not a
> > > very well hought out extension that has no means of coping with ipv6' if
> > > the compact extension can be modified to deal with IPv6 easily.
> > 
> > The extension was well thought out in that it saves a lot of bandwidth
> > in the context of the current BT protocol.  It's not well thought out in
> > that it assumes binary ipv4 addresses and nothing else.  You can fix
> > that with any number of ad-hoc extensions, but I guess I'm just saying
> > that perhaps its successor might consider the idea of being both
> > extensible in the future and a compact binary format.
> Might I suggest a "compact=2" data format consisting of tuples along
> the lines of:
> <byte:protocol#><4/16bytes:addr(size by prot)><2bytes:port>
> Where the protocol# byte comes from RFC 1340 (available at
>, and other locations).
> This would be 0 for IPv4, and 41 for IPv6. The one issue is indicating
> which types are acceptable, likely simply a list of bytes during the
> request.

Because this is minor tinkering at the edges of the protocol that makes
very little difference (the difference between binary ipv4 and compressed
ascii ipv4 addresses is only about 40%, so if thats whats limiting your
number of peers it doesnt help that much).

RFC1340 is not a suitable choice (although maybe there are people
who want to run BT over CRTP (Combat Radio Transport Protocol)). 41 is for
ipv6 in ipv4 tunnelling, and 0 is not ipv4. Its what tells you whether your
ip packet is TCP (6) or UDP (17).


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