[BitTorrent] Reducing dependency on trackers

Gregorio Roper gregorio at gmx.li
Thu Aug 26 02:51:41 EDT 2004


Olaf van der Spek wrote:
>>I think as a measure to increase performance in an environment of
> 
> unreliable
> 
>>trackers it would be helpful to have messages for requesting/sending lists
> 
> of
> 
>>peer addresses.
>>
>>I'm sure this has been proposed before and I know Shareaza is already
> 
> using some
> 
>>kind of message for that purpose. I intend to add support for messages of
> 
> that
> 
>>kind for LimeWire. In case you agree, I would like to use one of the
> 
> extension
> 
>>bits in the BT handshake to indicate support for that message, - otherwise
> 
> I
> 
>>would just exchange this message among LimeWire nodes.
>>
>>The message format I had in mind was a PEER_ADDRESS_REQUEST message with
> 
> no
> 
>>further payload for requesting addresses and a PEER_ADDRESS_REPLY message
>>containing a simple list of 6 byte addresses (4 ip bytes in big-endian
> 
> order and
> 
>>2 port bytes in little-endian order).
> 
> 
> Why little-endian for the port number?
> And what about DoS attacks?

I can use big endian port numbers if you prefer, - I'm really not married to any 
byte order. As far as DoS attacks are concerned, we have a certain experience 
with that kind of feature from Gnutella.

The feature of course relies on clients being well-behaved, for example 
blacklisting ip addresses for a while after they failed in order to reduce the 
number of connection attempts made to them, or passing on only IP addresses that 
you verified to be online and to accept incoming connections.

DoS attacks are only possible if some of the clients do not verify source 
addresses before passing them on.

mfg
gregorio


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