On Jan 24, 2008, at 12:45 PM, Matthew Toseland wrote:
We take the median of the average ping time for each node. Then we
smooth it
over a bit over time.
And because of the calculation both remote and local requests were
being rejected.
I don't see how this is possible.
Since this appears to be exploitable as a DoS, I have changed the
calculation to be based on the source (or average if a local request)
[r17235], which makes more sense to me anyway.
Does it? The average ping time is a reliable indicator of the node
being
severely overloaded on CPU, network or some other vital resource.
Well, in this case it was a reliable indication that one of our peers
maybe being overloaded (or defunct); and supposing that this node
appears consistently bad to all it's peers, then as a whole the
network does route around this node, but at one-extra-peer radius (it
does so because my node is rejecting requests in his favor).
With respect to measuring CPU/network/etc. A ping average is a ping
average, you're only measuring packet ack times (and then... available
bandwidth). Think about it backwords... If an overloaded node with a
high CPU load has a high ping average, then we should not route to
them (backoff?). Not start refusing requests from our peers.
The underlying problem might be that the ping average is a feedback
loop that can somehow be stuck ON. If a peer is marked as being super-
latent, we will not send any packets to them, and thus we can't see
that the latency is wrong. If the code is even written to such a
respect, if that peer would then want to send us anything he would be
ack'ing old packets (possibly making us think he is more latent???).
--
Robert Hailey
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