The Nucleus Ethernet Default MTU is set too large at 1514

Discussion created by dan_schiro on Aug 6, 2012


Default MTU is too large in a number of the Nucleus Ethernet drivers.  The MTU is set to 1514 which breaks starting with NET 5.2.


In NET 5.2, the code to calculate the maximum send size was  modified to use the device MTU set by the device driver instead of a  hard-coded macro.  This was done so this would be set properly  regardless of the device type being used, and NET would be flexible when  new interface types were added.  However, a problem occurred, because  ethernet drivers are not consistent in how they set this value.  Some  drivers set it to 1514, and some set it to 1500.


The RFC's for Ethernet and PPP specify a maximum MTU of 1500.  Drivers that have an MTU of 1514 are in violation of the RFC's and need  to be fixed by setting the default MTU to 1500 or less.