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 _______________________________________________ Ietf mailing list Ietf@xxxxxxxx https://www.ietf.org/mailman/listinfo/ietf