Hi,
I have strange problem. I have IPsec VPN tunnel between 2 buildings. In past (firmware version about 6.45) I was able transfer data via tunnel about 6 MB/s = 48 mbit/s in both directions.
After upgrade of firmware (I don´t remember version, but it was 6.46 or 6.47) I started see, that speed in one way decreased significantly to 1,7 - 2 MB/s. Speed in opposite way is still same (about 6 MB/s). Details are on attached picture. No other configuration change was performed except of firmware upgrade.
I tried perform bandwidth tests and it looks like MTU issue. If default MTU 1500 bytes is used, packets need fragmentation what result in lower speed. (there are PPPoE and IPsec header). If I decreased MTU in bandwidth test to some lower value like 1300 bytes, I was able measure higher speed.
(Zyxel is using "MSS Adjustment Auto" option, so I guess this is reason why one way is not affected. Is there similar option in MikroTik ?)
I would like to ask you for your opinion on this issue. And if this is caused by MTU as I suspect, is there any option to lower MTU on input interface to prevent fragmentation ?
(I tried change/lower MTU on interface ether1 where internet line is connected, but it didn´t help).
Any advise is appreciated.
Thank you in advance
Best regards
Milos