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Anumrak
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PPPoE client default MTU

Sat Nov 18, 2017 2:05 pm

Why here default mtu/mru are 1460, when i got always 1480? And you saying its default.
https://wiki.mikrotik.com/wiki/Manual:Interface/PPPoE
 
msatter
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Re: PPPoE client default MTU

Sat Nov 18, 2017 2:34 pm

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.
Two RB760iGS (hEX S) in series. One does PPPoE and both do IKEv2.
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Anumrak
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Re: PPPoE client default MTU

Sat Nov 18, 2017 3:08 pm

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.
You mean that I can see only maximum mtu, which is 1480 with IP header? And minimal is 1460 with IP + TCP, which is only theoretical and doesn't written in interface?
Last edited by Anumrak on Sat Nov 18, 2017 4:36 pm, edited 1 time in total.
 
pe1chl
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Re: PPPoE client default MTU

Sat Nov 18, 2017 4:34 pm

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.
 
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Anumrak
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Re: PPPoE client default MTU

Sat Nov 18, 2017 4:45 pm

I see. Support, maybe you should change default MTU/MRU in wiki on 1480? https://wiki.mikrotik.com/wiki/Manual:I ... Properties
 
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Anumrak
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Re: PPPoE client default MTU

Sun Nov 19, 2017 9:30 am

Up.
 
pe1chl
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Re: PPPoE client default MTU

Sun Nov 19, 2017 11:19 am

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.
 
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Anumrak
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Re: PPPoE client default MTU

Sun Nov 19, 2017 11:26 am

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.
I know, but these 1460 mtu in description so bad looking :)
 
pe1chl
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Re: PPPoE client default MTU

Sun Nov 19, 2017 11:33 am

So you require immediate attention during the weekend? On the ignore list you go...
 
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Anumrak
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Re: PPPoE client default MTU

Sun Nov 19, 2017 11:58 am

So you require immediate attention during the weekend? On the ignore list you go...
No-no, it's okay. I'll just wait for monday :)

P.S.: I can't go in ingnore list of whoever :)
 
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blajah
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Re: PPPoE client default MTU

Sun Nov 19, 2017 10:47 pm

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).
I have bigger routing table.
 
pe1chl
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Re: PPPoE client default MTU

Mon Nov 20, 2017 12:16 pm

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).
 
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Anumrak
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Re: PPPoE client default MTU

Tue Nov 21, 2017 9:58 am

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).
Relax, I'm just expert network engineer and love MikroTik routers :)
 
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blajah
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Re: PPPoE client default MTU

Tue Nov 21, 2017 9:37 pm

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, no there was no anger intended :) Its all good. And one more info, while i was working for biggest ISP here in Serbia, on one IX ( i'm not sure if it's fair to write ASN ) , MTU on their side was set to 1480. You can imagine how L1 tech support was happy with 500.000 ADSL users calling :)
I have bigger routing table.
 
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Anumrak
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Re: PPPoE client default MTU

Mon Dec 04, 2017 1:47 pm

1480 is OK.
 
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Re: PPPoE client default MTU

Tue Dec 05, 2017 3:07 am

Using NTT's environment in Japan, the MTU / MRU is 1454.
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Re: PPPoE client default MTU

Fri Nov 01, 2019 6:09 pm

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.
How do I change the MTU of the PPPoE Client? It doesn't allow me to do it, it appears in gray and I can't modify it.
 
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Re: PPPoE client default MTU

Sat Nov 02, 2019 1:18 pm

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).
 
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Re: PPPoE client default MTU

Sun Nov 03, 2019 1:23 am

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
 
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Re: PPPoE client default MTU

Sun Nov 03, 2019 1:27 am

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
Max MTU and MRU apply in 1492: http://prntscr.com/prp17k

I lose packages the same way. http://prntscr.com/prp0tu
 
pe1chl
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Re: PPPoE client default MTU

Sun Nov 03, 2019 11:35 am

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.
 
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Re: PPPoE client default MTU

Sun Nov 03, 2019 2:18 pm

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.
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?

I also clarify that I always have a 20-byte difference between WAN and PPPoE if I write 1512 in WAN I get 1492 in PPPoE but in the same way where I change the MTU I always get 1480 in the "Eth2" LAN
 
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Re: PPPoE client default MTU

Sun Nov 03, 2019 5:45 pm

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.
 
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Re: PPPoE client default MTU

Sun Nov 03, 2019 6:11 pm

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 have a Huawei modem in bridge mode with a UTP cable to the eth1 of the mikrotik and eth2 to my PC, the modem + PPPoE I have a MTU of 1492. modem + Router + PPPoE I have a MTU of 1480 on my PC
 
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Re: PPPoE client default MTU

Sun Nov 03, 2019 6:42 pm

Is that ether2 inside a bridge? If yes what is the Actual MTU of your Bridge interface?

From your other post the PPPoE client uses 1492 Byte of MTU just fine... So the problem is not in your PPPoE client...

Also try to ping from your router with DF enabled, not your computer, and check if you can pass packets larger than 1480 Byte
 
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Re: PPPoE client default MTU

Tue Nov 05, 2019 12:18 am

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?
Mikrotik has a default mtu of 1480 for the pppoe-client interfaces.

If you say
/interface pppoe-client set <your-pppoe-client-interface-name> max-mtu 1492
Or the equivalent command for winbox or webfig, It will re-connect and re-negotiate with 1492. At least in my 6.46beta59 mikrotik, it might depend on the version.

mtu parameter is a bit misleading, as it appears in a few screens and in some of them it is just informative. In the case of ppp or pppoe connections it is part of the negotiation process.

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