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Date: Tue, 29 Jul 2008 20:28:18 -0700
From: "John T. Yocum" <jtyocum@publicmx.com>
To: Sam Leffler <sam@freebsd.org>
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Cc: freebsd-net@freebsd.org
Subject: Re: ath using hostap sets MTU to 2290
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Quoting Sam Leffler <sam@freebsd.org>:

> John T. Yocum wrote:
>> Hello,
>>
>> I have a system running pfSense, which is built on top of FreeBSD =20
>> 7.0-RELEASE-p3. In the system I have an Atheros wireless card, =20
>> which when I enable hostap, changes it's MTU to 2290. If an =20
>> explanation is listed on a man page, I apologize, I did try =20
>> searching.
>>
>> Any ideas why this might happen? It doesn't appear to be a pfSense =20
>> issue, as it appears their code actually tries to set the MTU to =20
>> 1500.
>>
>> Only reason I ask here, is I noticed in my searching on Google, I =20
>> noticed others that aren't running pfSense have their MTU set to =20
>> 2290.
> MTU on an 802.11 network is 2290.  If you don't want the default =20
> then change it.  If you cannot then please provide the exact steps =20
> you take that do not work.
>
>    Sam

Thank you, I didn't realize that the default MTU was 2290. At the =20
moment, I am manually changing it to 1500, so I can setup a bridge =20
between wired, and wireless.

I'm curious, are there some Atheros cards or chipsets that only =20
support an MTU of 1500? I only ask, as it seems that some people don't =20
need to manually set the MTU to 1500.

Thank you,
John