Re: MTU 1640

Hi,

Now I did a bit of tracing on the WAN interface and i found out that
during the PPPoE LCP the PPPoE Client and Server are exchanging MRU
(Maximum Receive Unit) Information:

PPPoE Server -> PPPoE Client: Configuration Request MRU 1460
PPPoE Client -> PPPoE Client: Configuration Request MRU 1492
PPPoE Client -> PPPoE Server: Configuration Ack MRU 1460
PPPoE Server -> PPPoE Client: Configuration Ack MRU 1492

So the 1460 Bytes are comming from my ISP and are applied as MTU on my
interface. Like Lee Sharp says, i will leave the 30 Bytes. Thank you.

One way trace:
Server > Client
> Frame
> Ethernet
> PPP-over-Ethernet Session
> Point-to-Point Protocol
v PPP Link Control Protocol
    Code: Configuration Request (1)
    Identifier: 8 (0x08)
    Lengt: 14
    v Options: (10 bytes), Maximum Receive Unit, Magic Number
        v Maximum Receive Unit (1460)
              Type: Maximum Receive Unit (1)
              Lenght: 4
              Maximum Recieve Unit: 1492
        > Magic Number: 0xe5c12asd

Client > Server
> Frame
> Ethernet
> PPP-over-Ethernet Session
> Point-to-Point Protocol
v PPP Link Control Protocol
    Code: Configuration Ack (1)
    Identifier: 8 (0x08)
    Lengt: 14
    v Options: (10 bytes), Maximum Receive Unit, Magic Number
        v Maximum Receive Unit (1460)
              Type: Maximum Receive Unit (1)
              Lenght: 4
              Maximum Recieve Unit: 1460
        > Magic Number: 0xe5c12asd

Many thanks,

Jakob

On 26 December 2014 at 18:09, Lee Sharp <[email protected]> wrote:
> On 12/26/2014 03:12 AM, Jakob Schwienbacher wrote:
>>
>> Hi,
>>
>> Im running M0n0wall 1.8.1. Im using PPPoE to connect to my ISP. I had some
>> trouble with MTU size, then i saw my WAN MUT is set to 1460:
>
>
> Several things here...
>
> First, reboot resets m0n0wall back to stock.  All that custom config stuff
> outside of the actually config xml file is lost.  Makes hacking nice as a
> reboot fixes whatever you broke. :)
>
> Next, PPPoE is had, because very few people have it anymore for testing.  I
> was one of the last, and lost it 6 months ago.
>
> So, 1492 is the theoretical max.  But people were still having problems that
> seemed MTU related.  And it was found that a few places using PPPoE were
> also packaging more crap in the packets than 8 bytes.  Going a little
> further than needed fixed a lot of problems that we could not properly
> troubleshoot.
>
> Now, if you want to play with it, please do!  You will have to set
> everything from the CLI as using the GUI to tear it down and rebuild will
> probably reset it to 1460.  I have not seen the actual code.  Other did that
> work...  So you would probably gain a lot by unpacking an image and really
> looking at how things come together in that segment of the code.
>
> The question is, do you really want to do that for 30 bytes?
>
>                         Lee
>
>
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