Some months ago, in possibly more than one other thread, there was a discussion about the maximum configurable MTU size for various modem devices.
I decided to look at my spare ZyXEL VMG1312-B10A, which is pure vanilla, and has a (relatively) recent ZyXEL firmware image loaded. I looked via the GUI, as that is the most obvious and natural way an average user would configure such a device.
In the following table the wording of the column headings, and individual entries, is that as used by the GUI display.
Type : Mode : Encapsulation : MTU Size
ADSL/VDSL over PTM : Routing : PPPoE : 68 - 1492
ADSL/VDLS over PTM : Routing : IPoE : 68 - 1500
ADSL over ATM : Routing : PPPoE : 68 - 1492
ADSL over ATM : Routing : PPPoA : 68 - 1500
ADSL over ATM : Routing : IPoE : 68 - 1500
ADSL over ATM : Routing : IPoA : 68 - 1500
ADSL/VDSL over PTM : Bridge : - : -
ADSL over ATM : Bridge : - : -For those requiring baby jumbo frames, in bridging mode, there is a
patched firmware image, available from
johnson, which allows such a configuration.