I been migrating our sites from Cisco ASA to Meraki (Main Site MX250) (Branch office MX64), I found a lot issues regarding file transfers SMB, FTP is insane, I never had these issues with our ASA even when our ISP circuits were small at that time only 5MB it was saturated at least at 3MB or now we had 15MB on all our remote sites and it doesn't' even pass from 1MB, FTP or SMB, we have 43 branch sites, all the same, we have tested this without AMP, no bandwidth throttling policy, no flow control on the servers, no SMB signing on the servers, Iperf actually use all the bandwidth on the tests, latest beta firmware (without this we had response times between 100ms to 150ms on the branch offices), after the upgrade the latency was reduced between site is 5ms to 20ms, find on the community forum other options that I have already tried netsh int tcp set global timestamps=enabled same issue. When I call to support I don't get any answers or at least a light on this, just always the same excuse saying that this is on the ISP side, I recently called the ISP we tested the circuits and there is nothing wrong with the circuits, even the speedtest are normal. I recently found a post from guy in spiceworks mentioning something like this. Good idea to check your Meraki WAN config for "Do not Fragment packet" statement. Next to the MTU limit. This will free your flow. I had the same issue with a Site-to-Site VPN on a Sonicwall NSA 3600. But I can't find that option to give it a try.
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