Subject: Re: tcpdump and wi(4) (was Re: ipsec, path mtu, and fragmentation)
To: None <>
From: David Young <>
List: tech-net
Date: 02/06/2004 23:22:42
On Sat, Feb 07, 2004 at 02:24:18PM +1100, Daniel Carosone wrote:
> On Fri, Feb 06, 2004 at 11:27:00AM -0600, David Young wrote:
> > On Fri, Feb 06, 2004 at 08:22:40PM +1100, Daniel Carosone wrote:
> > > Why is tcpdump an off switch for wi(4)?
> > 
> > I know that through firmware revisions 1.4.9, Prism 2.5 cards do not do
> > the RTS/CTS handshake properly when promiscuous mode is on.  Perhaps your
> > client or AP has RTS/CTS enabled? See if there is any change when you
> > run tcpdump with the -p option.
> Indeed there is! It now continues to run at the expected rate.
> wi0 at pcmcia0 function 0: NETGEAR MA401RA Wireless PC, Card, ISL37300PEval-RevA
> wi0: 802.11 address 00:09:5b:23:43:f7
> wi0: using RF:PRISM2.5 MAC:ISL3873B(PCMCIA)
> wi0: Intersil Firmware: Primary (1.0.7), Station (1.3.6)
> wi0: 11b rates: 1Mbps 2Mbps 5.5Mbps 11Mbps
> I shall try and chase down a firmware upgrade for the card, and look
> at the AP config for RTS/CTS as well.  Would that be on by default,
> it's not something I recall changing.

The short answer is that I do *not* expect RTS/CTS to be be on by default.

The long answer is that a standalone AP will not usually use RTS/CTS
because, by definition, no stations are hidden from it. Its clients
might use RTS/CTS, however.  If an AP is near other APs (on a university
or corporate campus, say) then it might use RTS/CTS to protect its
transmissions from clashing with transmissions from neighboring APs.

I wish that I could recommend a f/w version that I *know* has fixed
this problem. Start w/ 1.5.6. There is firmware for download somewhere


David Young             OJC Technologies      Urbana, IL * (217) 278-3933