Re: [Madwifi-users] Understanding header lengths in 802.11.

[Alfred A. <al...@cc...>]

Hi,

>1. When doing some tests I get 214 bytes of Etherney type II packet.
>while
>the Atheros
>driver says it received 236 bytes from the HAL.
>=A0=A0=A0=A0=A0=A0=A0 - Where is the 22 bytes extra coming from?

802.11 packet header =3D 24 Bytes
                      + 4 bytes (if WEP is used)
                      + 8 bytes for SNAP header

i.e. 36 bytes opposed to 14 bytes for Ethernet.  If you're using WDS links
or better encryption schemes, the difference becomes even larger.

>2. How is the type field in the ethernet type II packet represented in
>the
>802.11 mac ?

Ethernet II frames with a type instead of a length field are wrapped into
an LLC/SNAP header.  Other 802.x media that don't support Ethernet II
framing do the same (e.g. Token Ring).  See RFC1042 and IEEE 802.1h for
details.

Best regards

Alfred Arnold

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