I've searched a lot and haven't found an answer to this question so I bit the bullet and have to ask, thank you in advance for any help.
We are a pharmacy and I've setup a L2TP connection with IPSec through the LTE connection in a wAP LTE kit US (https://mikrotik.com/product/wap_lte_kit_us) that I'm using for an external employee in a hospital. This has to be HIPAA compliant so logic tells me to use IPSec. Of course throughput using IPSec is an issue so I want to maximize the connection, especially between the remote Windows computer and local Windows Server.
I've tried different MTU settings but seems a lotta hassle so I just wanna compute the MTU but there's no info anywhere about my setup in terms of LTE header + L2TP header + IPSec header + TCP/IP header. The LTE interface is reporting an MTU of 1480 and if I change it to anything larger, it will cease to function. I've setup both the L2TP server and client with a MTU of 1400 and "Change TCP MSS" to YES in the PPP profile. Seems to work but still I can only wring ~35% of the 25mbps LTE data.
Bandwidth test between Mikrotiks says 6 mbps but as I see it, the remote computer still has a lotta headroom because when it's communicating and having a bad time waiting for data, I see the L2TP client at less than 1 mbps, per the "Interfaces" menu's rate and the wAP's CPU is nowhere near maxed out. Also, I don't know if Mikrotik's bandwidth test is representative of SMB performance in "virtual local network", if I may.
Have any of you done this type of setup and have some useful values I can use?