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Date: Fri, 17 Feb 2006 09:59:47 -0800
From: Sam Leffler <sam@errno.com>
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Cc: freebsd-net@freebsd.org
Subject: Re: ATH max packet size?
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Sten Daniel Sørsdal wrote:
> I am still waiting for my PCI -> MiniPCI bridge for my CM9 card so i am 
> unable to test this, and even though i read the source i am still 
> unsure, so i was hoping a kind generous soul would answer my question;
> 
> What is the max packet size (mtu) available using the ath driver?
> 
> The reason i ask is, i want to setup a tunnel between two units and 
> optimally not have to deal with any fragmentation issues.
> 

 From net80211/ieee80211.h:

/*
  * Maximum acceptable MTU is:
  *      IEEE80211_MAX_LEN - WEP overhead - CRC -
  *              QoS overhead - RSN/WPA overhead
  * Min is arbitrarily chosen > IEEE80211_MIN_LEN.  The default
  * mtu is Ethernet-compatible; it's set by ether_ifattach.
  */
#define IEEE80211_MTU_MAX               2290
#define IEEE80211_MTU_MIN               32

ath can actually handle very large packets (64K I believe) but the 
current driver won't chain rx descriptors together so it's limited to an 
mbuf cluster (2K).

	Sam