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