Hi!
The MX67 throughput is limited when the Advance Security features are enabled. An alternative to increase the throughput might be disabling IDS/IPS, AMP and Content filtering rules. Also if the traffic traverse a VPN tunnel the connection will slow down.
https://documentation.meraki.com/MX/MX_Overviews_and_Specifications/MX67_and_MX68_Datasheet
In order to get the full 2Gbps, you might need to change the MX for at least an MX95.
https://documentation.meraki.com/MX/MX_Overviews_and_Specifications/MX95%2F%2F105_Datasheet
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