[p2p-hackers] Why UDP and not TCP?

prova provaluator at yahoo.de
Mon Dec 6 11:11:57 UTC 2004


Am 04.12.2004 um 07:07 schrieb David Barrett:

> Great, thanks for the detailed answer.  I’d love to hear more stats on 
> this as you learn them.
>
>  
>
> Incidentally, does Limewire (or any of the major P2P networks, for 
> that matter) have a centralized stat-gathering mechanism? 

I guess so. Although it looks like they have some kind of bot that 
scans the network.
http://www.limewire.com/english/content/netsize.shtml

Steffen

>  
>
>
> From: p2p-hackers-bounces at zgp.org [mailto:p2p-hackers-bounces at zgp.org] 
> On Behalf Of Greg Bildson
> Sent: Wednesday, December 01, 2004 10:51 AM
> To: Peer-to-peer development.
> Subject: RE: [p2p-hackers] Why UDP and not TCP?
>
>  
>
> David,
>
>  
>
> Our operating environment has not yet stabilized - early beta testers 
> didn't get the proper port stability tests and our entire user base 
> has not been upgraded.  However, early indications are that 50 to 60 
> percent of firewalled users will benefit.  Again though, the harshest 
> firewalled users probably have not had a good experience with P2P 
> software so we are working with a self selected crew.   This method 
> does work with the Windows XP firewall so we expect it to be widely 
> successful as XP becomes further adopted. 
>
>   
>
> One improvement that we can make is to our existing scheme is to 
> handle firewalls/NATs that use a sequential port assignment algorithm 
> for each attempt.  Rather than just trying a fixed port, we could try 
> to negotiate a connection with that port +1, +2 and +3.  I'm not sure 
> what percentage of users would really benefit from this though.
>
>  
>
> As has been mentioned here recently, we certainly have noticed that 
> incoming TCP connections are often possible after the same type of UDP 
> pinging.  We have no numbers on that though.
>
>  
>
> Thanks
>
> -greg
>
> -----Original Message-----
> From: p2p-hackers-bounces at zgp.org 
> [mailto:p2p-hackers-bounces at zgp.org]On Behalf Of David Barrett
> Sent: Tuesday, November 30, 2004 7:35 PM
> To: 'Peer-to-peer development.'
> Subject: RE: [p2p-hackers] Why UDP and not TCP?
>
> That’s pretty sweet.  Do you know what fraction of firewalls “in the 
> wild” allow for this capability?
>
>  
>
> I’m no firewall nor security expert, but I was under the impression a 
> typical corporate firewall blocks most TCP ports, and virtually (or 
> even) all UDP ports.  Do you have any stats on what fraction of 
> firewall users are able to take advantage of this feature?
>
>  
>
> -david
>
>  
>
>
> From: p2p-hackers-bounces at zgp.org [mailto:p2p-hackers-bounces at zgp.org] 
> On Behalf Of Greg Bildson
> Sent: Tuesday, November 30, 2004 5:00 PM
> To: Peer-to-peer development.
> Subject: RE: [p2p-hackers] Why UDP and not TCP?
>
>  
>
> David,
>
>  
>
> Yeah, the code has been in beta for a while. 
>
>   
>
> It is UDP based.  If all UDP is blocked then it won't work and wont be 
> attempted.  We do a lot to first ensure that you can receive solicited 
> UDP which is what this feature relies on.  i.e. If you send a packet 
> to X via UDP and you are behind a NAT/Firewall, you can receive a 
> response back.  In LimeWire terms, you are then said to be firewall 
> capable and your searches and responses indicate this. 
>
>   
>
> There are many ways to negotiate the initiation of the connection on 
> both sides.  LimeWire has a concept of a push proxy for firewalled 
> hosts so we actually use that to deliver a special PUSH message that 
> tells the host to initiate a UDP connection to ip:port.  Both ends 
> then start sending UDP messages at each other and shortly thereafter, 
> they should both be able to receive those messages.  A type of TCP 
> style connection negotiation begins from there.  Just to be clear, 
> this is not proxying.  The only thing that is proxied, is the PUSH 
> message to trigger the actions of the uploader.
>
>  
>
> The FAQ is out of date.
>
>  
>
> Thanks
>
> -greg
>
> -----Original Message-----
> From: p2p-hackers-bounces at zgp.org 
> [mailto:p2p-hackers-bounces at zgp.org]On Behalf Of David Barrett
> Sent: Tuesday, November 30, 2004 6:28 PM
> To: 'Peer-to-peer development.'
> Subject: RE: [p2p-hackers] Why UDP and not TCP?
>
> How does the Firewall-to-Firewall portion of Limewire work?  Does it 
> use un-firewalled clients as relay servers?  It doesn’t sound like it, 
> but I thought that’s the only solution that truly works in all 
> situations.
>
>  
>
> The “features history” page mentions this on the entry for 8.12.2004:
>
>  
>
> “Firewall to Firewall transfers allows two people behind firewalls to 
> connect directly to each other and transfer data. This makes use of 
> UDP, and a third party to coordinate the initial messaging. … 
> Normally, firewalled users would only be able to download from other 
> hosts who are not firewalled, which is of course severely limited. 
> With firewall to firewall transfers, firewalled users can now access 
> the full 100% of hosts.”
>
>  
>
> This implies something like the NAT-to-NAT trick works with firewalls 
> also.  I’m a little shaky on how UDP works with firewalls, do both 
> clients initiate a conversation with a third party, and then the third 
> party hands back information IP/port information of the 
> pre-established out-bound connection?  How does this work if the 
> firewall simply blocks all UDP traffic?
>
>  
>
> However, the website is either out of date or there’s more to the 
> story because the FAQ says:
>
>  
>
> http://www.limewire.com/english/content/faq.shtml#fir1
>
>  
>
> “Q: What if I’m behind a firewall?
>
>  
>
> A: LimeWire will work when a user is behind certain types of 
> firewalls, but will not work behind certain other types. If you are 
> behind a firewall, you will not be able to download anything from a 
> user that’s also behind a firewall. In general, if you can connect 
> (you will see your “connection status” in the lower left hand corner 
> of the application) using LimeWire, you should be able to download and 
> upload files, but LimeWire will not work if you have either a web-only 
> proxy or a SOCKS proxy.”
>
>  
>
> What’s the full story?
>
>  
>
> -david
>
>  
>
>
> From: p2p-hackers-bounces at zgp.org [mailto:p2p-hackers-bounces at zgp.org] 
> On Behalf Of Greg Bildson
> Sent: Tuesday, November 30, 2004 2:12 PM
> To: Peer-to-peer development.
> Subject: RE: [p2p-hackers] Why UDP and not TCP?
>
>  
>
> If you believe that there are problems with LimeWire, you should 
> submit them to bugs at limewire and they will be looked into promptly.   
> If you have not already, you should also upgrade to version 4.2.3 to 
> get rid of some potential startup issues with old GWebcaches.
>
>  
>
> LimeWire is a "good new" p2p application - check out that 
> firewall-to-firewall transfer in the new version.  ;)
>
>  
>
> Thanks
>
> -greg
>
> -----Original Message-----
> From: p2p-hackers-bounces at zgp.org 
> [mailto:p2p-hackers-bounces at zgp.org]On Behalf Of 
> Digitalgruvmoves at aol.com
> Sent: Monday, November 29, 2004 9:10 PM
> To: p2p-hackers at zgp.org
> Subject: Re: [p2p-hackers] Why UDP and not TCP?
>
> Whats a good new p2p filesharing download to use? Limeware just 
> started acting nuts.
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