Subject: Re: adding an 802.11 data link type
To: None <>
From: Bill Studenmund <>
List: tech-net
Date: 08/05/2002 14:32:14
On Mon, 5 Aug 2002, David Young wrote:

> I would like to add an 802.11 DLT to NetBSD so that I can observe 802.11
> mgmt/ctl frames through bpf.
> In the discussion on the 802.11 DLT in May, it appears that a rough consensus
> was reached, namely that
>  0) DLTs DLT_802_11, DLT_PRISM_802_11, DLT_AIRONET_802_11 are desirable
>     in addition to DLT_EN10MB.
>  1) A driver supporting more than one DLT will call bpf with a new
>     procedure, bpfattach_multidlt, passing bpfattach_multidlt a mask
>     describing the DLTs the driver supports.
>  2) 802.11 interfaces will default to handing up 802.3 frames to bpf,
>     so that dhclient, tcpdump, etc. do not break.
>  3) Two new ioctl's list/choose the DLT used by bpf:
>       BIOCGDLTS -- returns a bit vector. "Lit" bits indicate supported DLTs.
>                    For example, on an 802.11 interface, the DLT_EN10MB'th
>                    bit and the DLT_802_11'th bit will be set.

As everyone said, an array is better.

>       BIOCSDLT  -- change the DLT for the bpf socket to one of the supported
>                    types
>  4) a driver will only build frames that listeners want
> If this is not substantially how people desire for the 802.11 DLT to work,
> let me know.
> If somebody has already begun to program this feature, stop me.

Please go for it.

Take care,