WAN, using PPPOE, should I adjust MTU or is it automatic?

[lvrmsc]

(Note : not having issue / not attempting to fix anything, just trying to clear a possible misunderstanding on my side).

Assuming a WAN interface on some ethernet link with MTU 1500. The WAN is established through PPPOE ("IPv4 Configuration Type = PPPOE").

Could / should the MTU field be left empty ("If this field is blank, the adapter's default MTU will be used. This is typically 1500 bytes but can vary in some circumstances."), on the expectation that the overhead of PPPOE encapsulation will be taken into account, lowering the WAN MTU to 1492 ?

Or is it preferable to specify 1492 as the MTU ?
I have always had the habit to explicitly set 1492 in this case, and this is surely not incorrect, but isn't it useless?

[stephenw10]

It will automatically be set to 1492. If you run ifconfig you can see what the ppp interface and it's parent are using for MTU.

If your WAN/ISP supports it you may be able to set the parent NIC to 1508 in order to get the full 1500B across PPPoE.

Steve