[bittorrent] Choking based on network closeness?

Elliott Mitchell ehem at m5p.com
Tue Jul 12 18:49:51 EDT 2005


>From: Bill McGonigle <bill at bfccomputing.com>
> On Jul 11, 2005, at 14:46, Justin Cormack wrote:
> > It came up on the list before, and there were some uses for it. The 
> > main problem is that no one seems to have enough information to 
> > measure closeness, unless you actually work for a large ISP or run 
> > BGP.
> 
> I've looked at a few different techniques that might apply - 
> traceroute, pathchar, packet-tailgating.  Assuming 'closeness' is only 
> one decision criterion I'm not seeing a reason why traceroute wouldn't 
> be sufficient (but tell me otherwise).  You'd have to make some 
> assumptions about how many hops are behind those * * * routers but the 
> core internet routers seem to always respond properly, and that gets 
> you most of the useful big-picture topology.

Much more likely option, you /might/ be able to get the TTL. You don't
want to know about where all the hops are, merely the length of the
route.

> There are certainly broken routers, some edge routers that won't honor 
> the ICMP packets, and probably an OS that won't allow the user to send 
> ICMP packets.  But there is probably enough information most of the 
> time to make a good guess.  And, you'd always fall back to the 'fastest 
> peer' algorithm in the absence of other data.

More pertinent question, how many OSes /will/ allow users to send ICMP
packets? Allowing users to send ICMP packets is a massive security hole,
no serious OS will allow you to do so.


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