On Thu, Sep 25, 2008 at 01:28:19AM -0400, Avinash Patil wrote:
> Hi All,
> 
> We are using LGE custom NDA driver for Atheros AR5414 chipset. We have seen that this driver doesnt obey fragmentation
 threshold set using command wiconfig. 
> 
> command : wiconfig ath0 -g 500
> 
> Fragmentation threshold is set successfully; ifconfig command confirms the same.
> 
> ifconfig ath0 output :
> 
> $ifconfig ath0
> ath0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 1500
>         ssid LGE_3COM frag 500 nwkey 65536:"","","",0x000000004804de387fffffff4803f258
>         powersave off
>         bssid 00:1e:c1:2d:d7:40 chan 1
>         address: 00:05:c9:a1:c9:96
>         media: IEEE802.11 autoselect (OFDM54 mode 11g)
>         status: active
>         inet 192.168.1.20 netmask 0xffffff00 broadcast 192.168.1.255
> 
> $ping -s 1000 192.168.1.202
> PING 192.168.1.202 (192.168.1.202): 1000 data bytes
> 1008 bytes from 192.168.1.202: icmp_seq=0 ttl=64 time=3 ms
> 1008 bytes from 192.168.1.202: icmp_seq=1 ttl=64 time=2 ms
> 1008 bytes from 192.168.1.202: icmp_seq=2 ttl=64 time=2 ms
> 1008 bytes from 192.168.1.202: icmp_seq=3 ttl=64 time=3 ms
> 
> 
> When we see the packets captured using sniffer, packet size is 1080(> 500) which means that packets arent fragmented.
> 
> When we try to set fragmentation thershold using ifconfig command "ifconfig ath0 frag 500", command returns failure -
ifconfig: IEEE80211_IOC_FRAGTHRESHOLD: Invalid argument.
> 
> Please let us know reason which prevents driver from fragmenting packets and solution.

The ath driver doesn't handle frames fragmented ath the
802.11 layer (doesn't set IEEE80211_C_TXFRAG bit in
its advertised capabilities).  This is why ifconfig doesn't
let you set it.  AFAIK the wiconfig utility should only
be used with the wi driver.

However even if the driver did require fragmentation you
wouldn't be able to tell via ping since reassembly would
have already occured.

If you want ip layer fragmentation, set you mtu as desired
(ifconfig ath0 mtu ...).  Again, you won't be able to tell
the difference via ping but 'netstat -pip' should show increased
frag counts.  ip layer fragmentation is different from 802.11
fragmentation.

-seanb

-seanb