Just wondering why on RB911 and RB912 when looking at ether stats there is a high number of entries in “too long” : is it a issue with L2MTU : ie ether 1598 and wan is 1600 : strange as the devices on both sides of the ptp have no entries for too long ?
Could be either L2 or L3 MTU I believe. Are you seeing rx/tx-fragments increasing with the the rx/tx-too-long statistic? It would suggest nothing is breaking because the router is fragmenting everything to fit.
If you can describe the link we can help you determine the ideal MTU settings. We’d need to the type of connection and any protocols you are running on top like PPP, IPSec, etc…