On 30 May 2010, at 16:02, Arnt Gulbrandsen wrote:
On 05/30/2010 04:44 PM, Sabahattin Gucukoglu wrote:
BitTorrent is popular, yes. People at home *are* behind NAT boxes, with all
the usual pain that implies *. It's just that BitTorrent, being a
straightforward TCP protocol with no embedded payload addresses **, can
operate behind NATs, and those NATs can be configured either manually or
automatically by users or their client software ***. If the NAT should move
to the ISP, it seems possible that this is no longer true.
Not quite.
1. Bittorrent clients connect to each other via TCP. Each connection is
incoming at one end. Torrent clients mostly use UPNP to accept incoming
connections.
2. UPNP is an ethernet-level protocol (it uses UDP/IP broadcasts), so it
works only if the USER is on the public internet. Hence, NAT within the
user's network is now very different from NAT within the ISP's network.
That's why I said the wide popularity of bittorrent shows that USERS are on
the public internet.
Right, yes, I didn't see it from that standpoint. However UPnP can of course
be substituted by NAT-PMP/PCP or something else that doesn't have the same
discovery problem, and ISP-level NATs will no longer be a "Problem" for clients
needing incoming connections even though they can no longer be said to be
"Public". Of course we're assuming that clients are in direct contact with
their gateway here, I'm not sure how true that is, there may need to be added
proxying to replicate requests otherwise. It certainly isn't impossible to do.
Cheers,
Sabahattin
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