Subject: adding an 802.11 data link type
To: None <>
From: David Young <>
List: tech-net
Date: 08/05/2002 00:16:45
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.

      BIOCSDLT  -- change the DLT for the bpf socket to one of the supported

 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.


David Young             OJC Technologies     Engineering from the Right Brain
                        Urbana, IL * (217) 278-3933