Just to add a little more definition around this, we coincidentally just went through a somewhat in-depth MTU size exercise with Alcatel-Lucent regarding what the PMP320 and PTP600 can actually support.   In the end, after all the Wireshark traces were decoded, debated, and a consensus formed, its probably safe to say that the max MTU is actually better described (by the industry) as the max size of the "DATA PAYLOAD" portion of an Ethernet frame.   

Meaning, for today's PMP320, the max MTU is actually 1500 bytes.  This also aligns with the Config web page of the PMP320 CPE where you set the largest MTU size allowed.  The CPE will not let you enter any value larger than 1500 bytes.    Now, “under the hood” so to speak, when you add on the remaining bytes that make up the Ethernet header info (Source Addr, Dest Addr, Eth type, and then FCS at the end.... a total of 18 additional bytes), then the total ETHERNET FRAME size that PMP320 can handle is 1518 bytes.

 

Bottom line, there's a technical difference between the definition of MTU, and the total Ethernet frame size.

Just an fyi…..

Dave

Maximum MTU size for PMP320 is 1518 (1518 for SM and 1522 for AP). We don't currently have QinQ tagging support on the roadmap.  However within the MTU limits above we should be able to pass q-in-q packets while in the upcoming layer 2 bridge mode.