[LINK] iPhones & Cisco

Adam Todd link at todd.inoz.com
Wed Jul 18 10:02:46 AEST 2007



You know a simple solution to this is for routers (wireless or 
cabled) to actually reject duplicate requests from a node within a 
certain time frame.

I actually wrote a code chunk to do just this into Linux as I had a 
device that constantly did ARP requests and at one time a DSL 
provider (RequestDSL) was sending ME all their ARP traffic clogging 
my border router and loading it down.

After adding the code to build a table (with variable time outs of 
course) to discard any duplicate requests and send back a reply to 
second and subsequent requests with a loop back address, the problem 
seemed to solve itself quite quickly :)

It's easy to fix an arp request later if the problem continues and 
really, if a device is out of control or failing to be sensible, you 
want to cause it to behave in a way that you can see it's not 
operating properly.  Hence my choice to reply with a loopback address 
to most of the requests.  Of course, if there is a legitimate 
address, then a reply will be given for that address to every N 
requests, but all other requests are discarded, or replied with 
loopback, depending on the necessary behaviour of the faulty device.

The Device then communicates with itself and functionality goes 
"offline" it's REALLY easy to pinpoint the problem and rectify 
it.  It also removes broadcast storms.

Getting an answer back helps greatly :)

Good thing I don't have an iPhone :)

At 04:57 AM 18/07/2007, Stephen Loosley wrote:
>iPhones flooding wireless LAN at Duke University
>
>By John Cox, Network World July 17, 2007
><http://www.infoworld.com/article/07/07/17/iphones-flood-wireless-lans_1.html?source=NLC-TB&cgd=2007-07-17>
>
>The built-in 802.11b/g adapters on several iPhones periodically 
>flood sections of the Durham, N.C., school's pervasive wireless LAN 
>with MAC address requests, temporarily knocking out anywhere from a 
>dozen to 30 wireless access points at a time.
>
>Campus network staff are talking with Cisco, the main WLAN provider, 
>and have opened a help desk ticket with Apple. But so far, the 
>precise cause of the problem remains unknown. <snip>




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