said by vikingisson:I'm not following the question either. Even the 10/7 I'm using with a Sagemcom PPPoE sets MTU to 1492 like the old 1M DSL days. The last thing I'd do is to use the DSL modem as a switch, it lives off the WAN port of my router. I don't see any way to change what we get. You can do what you want on the LAN side.
Packet leaves your PC. It is a full 1500 byte frame. Traverses your switch. Still 1500 bytes. Reaches your router. Oh shit moment. Time to split the packet in two because there's only 1492 bytes of space inside a PPPoE frame to transport data. It's a question of efficiency. Some protocols get affected by this, and if you're trying to keep your traffic "clean" this winds up looking dirty 
On that note I really do wish we had a choice with modems. The cellpipe and sagemcom are both consumer grade all in one junkers when all I want is a dumb modem.
I don't think you realize the repercussions of shrinking the MTU. I think we should consider it *ideal* to achieve the same MTU across the network, so that you don't have to split up packets and what not. Nothing about this RFC has any provision for using the modem as a switch (not sure what you mean by that), and whether you use the modem as a router or just a bridge makes no difference aside from the fact that the modem firmware may or may not support this larger frame size.
The goal isn't to get a specific frame size across the board per se, it's more to remove the environment where packets need to be truncated/fragmented, or whatever else to fit into the standard mtu size.
said by nitzguy:The OP was on the really old HSIA service that didn't use PPPoE...
Unfortunately....with the move to PPPoE, you've entered the world of a 1492 MTU (which wasn't the case with the old service I believe)...
So, long story short, I think you're stuck 
This *is* RFC'd and in use by several ISP's... I don't think I'm stuck - we just need TSI to get on board
