Re: Wireless laptop roaming through various access points

William P.N. Smith <news05@xxxxxxxxxxxxxxx> hath wroth:

>"VDP" <rentorbuy@xxxxxxxxx> wrote:
>>They *do* connect
>>correctly but it seems that while one card's link is up, the second
>>doesn't try to connect to *its* AP
>
>I beleive this is a function of how WinDoze handles having more than
>one network interface (it ignores all but one of them).

Not exactly. All the multiple interfaces on my office machines (two
ethernet, wireless, Bluetooth, dialup modem, VPN, etc, are alive and
well at the same time. What's different is that MS can normally
handle only ONE default route (or default gateway) for internet
traffic. Whichever interface has the default route pointing to it,
gets all the internet traffic. I have several static routes pointing
to remote networks (i.e. VPN's) that direct some traffic to specific
destinations, but the internet traffic usually goes via the default
route. It is possible to assign more than one default gateway in the
configuration for a given network interface, which is useful for load
balancing, but usually does weird things because there's no RIP
protocol to redirect the traffic to the correct gateway.

What Windoze is suppose to do when juggling enabled and disabled
interfaces is to change the default route. This is usually not a
problem with the common wireless router because the IP address of
gateway is identical whether it's going via a wired or wireless
bridged link. Same thing with multiple access points connected to a
common gateway machine.

What needs to change is the ARP table, which maps the MAC address to
the IP address. The IP address doesn't change but the MAC address of
the access point should. In theory, spanning tree protocol (802.1D)
takes care of lost links at the MAC layer. In reality, it tends to be
a bit chatty and is rarely implimented in wireless bridges. It's just
not fast enough to deal with moving target networks. The new 802.11r,
which includes a fast version of STP, should solve the problem.

Meanwhile, if you just monitor the ARP table with:
arp -a
you can see if the client is switching between access points (i.e.
betweeen MAC addresses) as the MAC address of the default gateway will
change.

--
Jeff Liebermann jeffl@xxxxxxxxxxxxxxxxxxxxxx
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
.

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