ath using hostap sets MTU to 2290

John T. Yocum jtyocum at
Wed Jul 30 03:28:19 UTC 2008

Quoting Sam Leffler <sam at>:

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

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

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

Thank you,

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