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.