Date: Sat, 17 Aug 2002 14:15:37 -0600 (MDT) From: "M. Warner Losh" <imp@bsdimp.com> To: fscked@pacbell.net Cc: eyurtese@turkuamk.fi, mobile@FreeBSD.ORG Subject: Re: IBSS and BSS with multiple FreeBSD Wireless Gateways Message-ID: <20020817.141537.108956335.imp@bsdimp.com> In-Reply-To: <3D5E98FF.82CD061E@pacbell.net> References: <Pine.A41.4.10.10208171330130.4338-100000@bessel.tekniikka.turkuamk.fi> <3D5E98FF.82CD061E@pacbell.net>
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In message: <3D5E98FF.82CD061E@pacbell.net>
richard childers <fscked@pacbell.net> writes:
: You are WiFi- and FreeBSD-enabled; so is your friend. For the sake of
: simplicity let's assume that you are directly across from one another in two
: dormitories at approximately the same height.
:
: You both eliminate signal strength and signal security issues with
: line-of-sight antenna pointed directly into one another's cone of
: transmission.
Well, except that it is real easy to intercept the side lobes of most
antennas if you have proximity. I routinely am able to sniff packets
off of dish antennas that have a very small cone of transmission by
being very close.
: At this point you are not unlike two routers with a cable between them, and
: it is only a matter of picking an appropriate class 'C' subnet (IE,
: 192.something), assigning it an appropriately long mask (IE, one preserving
: only two bits of the address for actual networking), bringing the interfaces
: up and adding routing entries on each end.
Yes. I'm doing exactly what you suggest over 5.5 miles between my
house and a friend's.
: Note that your network is still hypothetically subject to eavesdropping and
: jamming from parties in either antenna's line of sight.
This is a real threat.
: A slightly more complicated scenario emerges when you attempt to add a third
: node; at this point one of the nodes needs to have two cards, with two
: addresses and two antennas and two routing entries.
:
: I imagine there are some issues with crosstalk between the antennas that
: would need to be addressed with physical separation and maybe some
: appropriate shielding; tin foil works, I expect.
Tinfoil won't cut it, I'm afraid. I've tried to shield things with
tinfoil and found that it was woefully inadequate, even when well
grounded.
Cross talk between antennas is a real problem. I have two on my roof
and have found that if I run them at the same frequency that there are
big problems. I have to run them at different frequencies to make
that work. And I gotta make sure that any access points I have inside
are on a third frequency, otherwise you get mutual interference when
there's lots of traffic.
Warner
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