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Date:      Fri, 3 Jan 2003 02:14:03 +0200 (WET)
From:      Evren Yurtesen <eyurtese@turkuamk.fi>
To:        dmagda@ee.ryerson.ca
Cc:        freebsd-stable@FreeBSD.ORG, wpaul@ctr.columbia.edu
Subject:   Re: wi0 and mtu setting
Message-ID:  <Pine.A41.4.10.10301030152550.16002-100000@bessel.tekniikka.turkuamk.fi>
In-Reply-To: <867kdnfevc.fsf@number6.magda.ca>

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But if you are using PPPoE then you should set the mtu of the pppoe
connections to 1492 because of the 8 bytes overhead of the PPPoE (if you
are not using encryption or compression)

So if a server sends a packets which are 1500bytes and plus 8bytes PPPoE
then it is 1508 bytes. So the sending interface should be able to set the
ethernet MTU to 1508 which is possible to use at least in prism cards
until 1600 bytes (I didnt test this in orinoco/lucent) not with freebsd of
course with mikrotik routeros

I think this option should be provided to user even though it breaks the
standarts to be used at own risk to set MTU higher than 1500. Maybe it is
not physically possible to set MTU higher than 1500 in normal ethernet but
this limitation obviously doesnt apply to wireless interfaces and gigabit
ethernet cards. 

Evren



On 2 Jan 2003, David Magda wrote:

> Evren Yurtesen <eyurtese@turkuamk.fi> writes:
> 
> > I wonder how come wi driver doesnt let me to set mtu higher than 1500
> > even though I know the card supports it?
> 
> Because the maximum size of the data poriton in a frame for 10Mbit
> and 100Mbit Ethernet is 1500.
> 
> > Will this be changed in a new version of the driver?
> 
> Not unless they change the standard. I believe 1Gbit Ethernet is
> slightly different but would have to look up specifics.
> 
> -- 
> David Magda <dmagda at ee.ryerson.ca>
> Because the innovator has for enemies all those who have done well under
> the old conditions, and lukewarm defenders in those who may do well 
> under the new. -- Niccolo Machiavelli, _The Prince_, Chapter VI
> 


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