On 30/08/2013 16:36, Benno Overeinder wrote:
On 08/30/2013 01:58 PM, Randy Bush wrote:
In a study using the RIPE Atlas probes, we have used a heuristic to figure out where the fragments where dropped. And from the Atlas probes where IP fragments did not arrive, there is a high likelihood the problem is with the last hop to the Atlas probe.
i wonder if this is correlated with the high number of probes being behind nats.
That would be a viable explanation, although we have not tried to fingerprint the probes to figure out if this was true.
If we will rerun the experiments in the future, we should spent more effort into identifying the router/middlebox that is giving the IP fragmentation problems (drops or blocking PMTUD ICMP).
Maybe this provides a bit of insight:
From a test last week from all RIPE Atlas probes to a single "known good" MTU 1500 host I compared probes where I had both a ping test with ipv4.len 1020 and ipv4.len 1502. behind NAT probes: 12% 1020 bytes ping worked while 1502 failed non-NATted probes: 6% ""
hth, Emile Aben RIPE NCC