too many padding bytes added to Ethernet frames sent on the network

When sending out short Ethernet frames, the minimum frame length definitions of IEEE 802.3 are not respected. The shortest frames sent out by our implementation are longer than expected.

According to IEEE802.3 definition, the minimum frame size (starting from Destination MAC Address and including the FrameCheckSum) is 64 byte.

However, our implementation will send out all frames padded to 68 byte (including FCS).

It is expected, that no unneccessary padding is added to the frames and thus short frames (e.g. DCP Identify Requests) do not have more than 64 byte (including FCS). This is independent from presence or absence of a VLAN tag in the frame.

Note that there is special behavior for Profinet RTC frames. These frames are padded by the RTC protocol definition and thus the shortest RTC frame (including FCS) will have a length of 68 byte. RTC frames are NEVER padded by the MAC layer, the padding is always done by the RTC protocol itself.