PPPoE is standard 1492 and that results in a minimal MTU of 1460 for normal packets as written. Now there are baby-jumbo frames and my PPPoE is 1500 which is resulting in 1472 to be pingable without defragmenting.
Your ISP has to support this.

Up.

Up.

Come on! When you want to contact support use mail. And it is sunday.
Furthermore this is a very unimportant issue. You can set the MTU to the value you like.

So you require immediate attention during the weekend? On the ignore list you go...

If you create PPPoE client on router, you would see that default value isn't 1460 or 1480, its auto. Why such a big deal? Auto would work even better then fixed value, and assuming you are leaving it @ default value, you do not care about it ( you do not have any specific requirement setting it this way or other).

If you create PPPoE client on router, you would see that default value isn't 1460 or 1480, its auto. Why such a big deal? Auto would work even better then fixed value, and assuming you are leaving it @ default value, you do not care about it ( you do not have any specific requirement setting it this way or other).

Yeah, but when you choose auto it uses 1480 where 1492 would be more optimal. So manually setting it is better when you know the actual limit.
Anyway, there is no issue at all, the guy was just freaking out over a small error in the documentation (and bumping his topic during the weekend to have that fixed).

If you create PPPoE client on router, you would see that default value isn't 1460 or 1480, its auto. Why such a big deal? Auto would work even better then fixed value, and assuming you are leaving it @ default value, you do not care about it ( you do not have any specific requirement setting it this way or other).

Yeah, but when you choose auto it uses 1480 where 1492 would be more optimal. So manually setting it is better when you know the actual limit.
Anyway, there is no issue at all, the guy was just freaking out over a small error in the documentation (and bumping his topic during the weekend to have that fixed).

No, PPPoE does not use an IP header. It has a couple of options, which make the header length variable, so the MTU/MRU is not really fixed.
MikroTik use a default MTU/MRU of 1480 so there is room for all possible PPPoE options, but when you just use it without options you can set the MTU/MRU to 1492.
(and indeed when the ISP supports it you can use MTU 1500)

MTU/MRU is different from TCP MSS! TCP MSS is MTU/MRU - IP header size - TCP header size. This means TCP MSS is usually 40 or 44 less than MTU/MRU.

Change the Max MTU and Max MRU on the "General" tab and the "Actual MTU" will follow that (unless you have set an impossible value).

Change the Max MTU and Max MRU on the "General" tab and the "Actual MTU" will follow that (unless you have set an impossible value).

I did it but on my PC for eth1 it still shows me a MTU of 1480: C

The ethernet MTU is completely unreleated to this! You should leave it at 1500 or set it to e.g. 1512 when your ISP supports RFC4638.
The MTU of the PPPoE interface is dynamically negotiated. You supply your own maximal accepted value and the peer has their max value, the result is the lower of the two.
When your ISP supports RFC4638 (most of them don't!) you can set the Max MTU and Max MRU to 1500 and the ether1 MTU to some higher value (minimum 1508) and you will get 1500 byte MTU/MRU.
But when they don't support it, it will fall back to a lower value, with MikroTik usually 1480. So then it is better to set 1492 and see if that is accepted.
After then connection is established, always check with ping (with size and don't fragment option) to see if it really works!
Lower the Max MTU and Max MRU until it does. This is not a MikroTik problem, it is a problem of your ISP.

You didn't post your config yet to see what you've set there, as you have some serious issues understanding this whole MTU thingie (what I get from your posts atleast).
Also, don't open another topic if you already asked in another. Makes tracking your issue kinda hard.

I understand, my ISP supports a MTU of 1492 by PPPoE if I connect my PC directly to the modem without the router my MTU is 1492 by PPPoE but when I activate the bridge mode and connect the Mikrotik my MTU changes to 1480, with neither previous router my MTU was 1492, in my case I get better results with a MTU of 1492 and not one of 1480, yesterday I tried to put a MTU of 1492 on all interfaces and I still get a MTU of 1480, my ISP does support a MTU of 1492 .. Why can't I change it?

/interface pppoe-client set <your-pppoe-client-interface-name> max-mtu 1492