[CUWiN-Dev] Re: IBSS Split aka BSSID wars?

Fri Feb 2 15:27:28 CST 2007

On Fri, Feb 02, 2007 at 05:48:12PM +0100, Ronald in 't Velt wrote:
> If I can briefly revive this old thread: Is there any more information on 
> those bugs you fixed? Can you recall / retrieve what changes you made and 
> when this was (roughly)? I am using the Madwifi (ng) driver for Atheros 
> chipsets under Linux. I believe that the net80211 MAC-layer in that driver 
> descends from the NetBSD one. I would like to check whether your fixes are 
> also part of Madwifi now.

I just scanned the NetBSD sources for changes that are relevant
to IBSS merges, according to my recollection.  The changes are in
sys/net80211/ieee80211_node.c and in src/sys/dev/ic/ath.c.

In src/sys/net80211/ieee80211_node.c:

----------------------------
revision 1.46
date: 2005/11/20 10:04:21;  author: dyoung;  state: Exp;  lines: +32 -23
Repair adhoc mode.

        1 Complete initialization of "faked up" ieee80211_nodes,
          whose capabilities and other fields are wrong, when we
          first receive a beacon or probe response from the
          corresponding neighbor.  This entails factoring
          ieee80211_init_neighbor out of ieee80211_add_neighbor.

        2 In adhoc mode, ic->ic_bss is present in the neighbors
          table, ic->ic_sta, and it is not necessarily the wrong
          node on which to mark statistics for a rx'd packet.  Do
          not reject ic->ic_bss and fake-up a new node without
          comparing its MAC address with the address of the sender
          in the rx'd packet.  This fixes a memory leak.

...

----------------------------
revision 1.37
date: 2005/01/04 00:56:52;  author: dyoung;  state: Exp;  lines: +4 -4
branches:  1.37.2;  1.37.4;
IBSS-merge clean-up, inspired by some Linux patches from Jon Anderson
(mail at janderson.ca): remove ieee80211_ibss_merge's TSFT argument.
Do the TSFT comparison in the drivers (ath, atw).  Remove a lot of
extraneous debug statements from ieee80211_ibss_merge.

Set the ieee80211_node's state to IEEE80211_STA_BSS after it's been
copied to the ic_bss, not before.

In struct ieee80211_node, make the ni_tstamp field a union of a
uint64_t and the 8 TSF octets so that it's easier to compare a
neighbor's TSF with the local TSF.

Log IBSS merges (Greg Troxel's suggestion).  Also log IBSS creation.
These are rare and important events that deserve to be logged.

************************

In src/sys/dev/ic/ath.c:

----------------------------
revision 1.68
date: 2006/03/02 03:38:45;  author: dyoung;  state: Exp;  lines: +444 -194
branches:  1.68.2;  1.68.4;
Miscellaneous ath(4) and net80211 updates and bug-fixes coming from
sam@ and various open source repositories:

ath(4):

        Ignore "phantom" beacon misses: should stabilize connections
        to access points (no more ceaseless link-UP/DOWN indications).
        Also, re-synchronize beacon timer using the TSF in the
        first beacon received after joining a BSS---this should
        also help suppress spurious beacon misses.  I am hopeful
        that this will help ath(4) lossage reported by perry@ and
        smb at .

...

----------------------------
revision 1.44
date: 2005/01/19 04:56:42;  author: dyoung;  state: Exp;  lines: +3 -3
branches:  1.44.2;
For a proper IBSS merge, we have to discard the old beacon packet,
create and queue a new one that carries the new BSSID.  I mined
net80211 in FreeBSD for the solution, which is to make an
IEEE80211_S_RUN->IEEE80211_S_RUN state transition---ath_newstate
discards the old beacon packet creates a new one by calling
ath_beacon_alloc.

I tested the merge as follows.  Starting at my desk on the second
floor of the building where I work:

soekris% ifconfig ath0 mediaopt adhoc ssid zzz chan 11 down

powerbook% ifconfig rtw0 mediaopt adhoc ssid zzz chan 11 up

soekris% sleep 25; ifconfig ath0 up

I raced to the elevator with my Powerbook, pressed the "Down"
button, got in, and pressed "Floor 1."  At the first floor:

powerbook% ifconfig rtw0 | grep bssid
        bssid 02:p:p:p:p:p chan 11

I waited 25 seconds.  I pressed "Floor 2."  At Floor 2, I returned to my desk.
I checked to make sure that the Soekris console read:

soekris% ath0: creating bss 02:s:s:s:s:s
ath0: bss merge 02:s:s:s:s:s -> 02:p:p:p:p:p

0:s:s:s:s:s is the Soekris' WLAN MAC.  0:p:p:p:p:p is the Powerbook's
WLAN MAC.  Each created an ad hoc-mode BSSID from its WLAN MAC by
OR'ing 0x2 with the first octet.

My Powerbook created a network while the Soekris radio was off.
The Soekris radio turned on while I was in the 802.11-impervious
elevator with my Powerbook.  When I returned to the second floor,
the Soekris "heard" beacons from my Powerbook as the elevator door
opened.  Since the Powerbook's network was approximately 25 seconds
older than the Soekris', and since it had the same SSID (zzz) as
the Soekris', the Soekris merged with the Powerbook's network (by
setting its BSSID) as it should.
----------------------------
revision 1.43
date: 2005/01/16 11:43:34;  author: dyoung;  state: Exp;  lines: +13 -3
branches:  1.43.2;
It's necessary to stop DMA on the beacon ring and reconfigure the
beacon after an IBSS merge, or else beacons transmissions may not
resume like we expect.  From Sam Leffler.
----------------------------
revision 1.41
date: 2005/01/04 00:56:51;  author: dyoung;  state: Exp;  lines: +21 -4
IBSS-merge clean-up, inspired by some Linux patches from Jon Anderson
(mail at janderson.ca): remove ieee80211_ibss_merge's TSFT argument.
Do the TSFT comparison in the drivers (ath, atw).  Remove a lot of
extraneous debug statements from ieee80211_ibss_merge.

Set the ieee80211_node's state to IEEE80211_STA_BSS after it's been
copied to the ic_bss, not before.

In struct ieee80211_node, make the ni_tstamp field a union of a
uint64_t and the 8 TSF octets so that it's easier to compare a
neighbor's TSF with the local TSF.

Log IBSS merges (Greg Troxel's suggestion).  Also log IBSS creation.
These are rare and important events that deserve to be logged.
----------------------------
revision 1.36
date: 2004/08/10 01:03:52;  author: dyoung;  state: Exp;  lines: +71 -11
IBSS fixes: get IBSS beacon generation right.  Merge with a same-SSID,
same-channel IBSS.

-- 
David Young             OJC Technologies
dyoung at ojctech.com      Urbana, IL * (217) 278-3933