I would like to ask is there a throughput difference between PPPoE MTU 1480 or MTU 1492?
Has anyone done comparisons?
If TCP stacks on end devices do PMTUD properly and router(s) don’t have to perform fragmentation, then the difference is less than 1% (12 bytes of difference in MTU divided with almost 1500 bytes is less than 1%). And that difference is only there for full-sized packets, in reality there’s a size distribution of packet sizes and many (if not most) packets are smaller than full 1500 bytes anyway.
If TCP stacks on end devices didn’t do PMTUD, then likely 1480 vs 1492 doesn’t make any big difference, full size packets have to be fragmented anyway and overhead is exactly the same. Only packets with sizes between 1480 and 1492 will get fragmented in one case and not fragmented in other case. In this case difference is around 3% (40 bytes of IP / TCP headers for additional fragment divided with almost 1500 bytes is slightly less than 3%). And, again, that’s only for packets with original size between 1480 and 1492 bytes and I expect those packets are not frequent (packet size distribution on my WAN interface shows less than 25% packets with sizes >1024 in both directions and I highly doubt all are at MTU size).
Hence my estimation: the overall throughput difference is (much) less than 1%.
Is this screenshot of a CPE ether stats providing any information to help me answer my question!
Sadly stats from MT don’t add any info to thinking in my previous post. The penultimate category (1024-1518) is just too broad and doesn’t give any information about 1480 vs. 1492 byte packets.