Mikrotik documentation in some instances give a range of 68…1600 for MTU settings (w/ the default set at 1500)
Whenever I try to set an mtu setting larger than 1500, I get an error return (e.g., could not set value)
Whenever I try to set an mtu setting smaller than 1500 – it works fine
Am I doing something wrong? or is Mikrotik limited to a 1500 byte MTU?
-Charles
P.S. – if this is true, please implement > 1500 byte MTU (support up to 1600 =)
MT is not inherently limited to 1500 mtu (under 2.9), but it does have such a limit on many types of interfaces.
Exceptions to that, that I know of, are:
(at least some) Atheros interfaces can be set as high as 1600.
(at least some) Intel pro-1000 interfaces can be set to 16110.
I don’t know of any 10/100 interfaces where MT allows large MTUs.
Also, the slightly larger MTU necessary for VLAN is allowed transparently on interfaces that support it. I.e. a virtual interface will work perfectly with a MTU of 1500, even if the parent also has an apparent 1500 MTU (if the interface allows it).
–Eric
After reading this we increased the MTU on our wireless links to 1600. We have a customer having IPSEC issues and we’ll see if this fixes the problem.
If all else fails and you are willing to, try to enable connection-tracking on all routeros (v2.9.x) units in the path and see if that helps. No need to worry about v2.8.x though 
Please let me know how it turns out.
Set mtu to 1500 before trying