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From: Janet on 16 Apr 2008 19:48
Here's a head scratcher:

We've got three Cisco Aironet AP's connected to a Cisco managed switch
and everything was working fine until someone brought their iPhone and
Mac in. When they turn them on, the other wireless clients get the "there
is
an IP address conflict" popup over the system tray and traffic on the
network
becomes erratic or stops.

As far as I know, all the devices on the network are DHCP. But as an
experiment, I temporarily changed the inside addresses on the whole
network from 192.168.0.X to 10.0.0.X. Like before, everything is
fine until these Mac/iPhone devices are turned on. Then everyone gets
the "there is an IP address conflict" popup again and traffic stops.

If we assume that, say, the Mac isn't DHCP and has an address programmed
into its stack (I'll go check it myself,) why would there be an IP address
conflict reported even on the new subnet? If, say, the Mac had 192.168.0.1
programmed into its stack, how would it conflict with any 10.0.0.X address?

Thanks.


From: John on 16 Apr 2008 20:07
You sure got me scratching my head. My wild guess is the subnet is too small
(there are more devices than available IPs)? Or the DHCP (Cisco Aironet?)
needs a bug fix? Does it have the latest firmware?

"Janet" <janet(a)nospam.com> wrote in message
news:OubqmxBoIHA.4904(a)TK2MSFTNGP03.phx.gbl...
> Here's a head scratcher:
>
> We've got three Cisco Aironet AP's connected to a Cisco managed switch
> and everything was working fine until someone brought their iPhone and
> Mac in. When they turn them on, the other wireless clients get the "there
> is
> an IP address conflict" popup over the system tray and traffic on the
> network
> becomes erratic or stops.
>
> As far as I know, all the devices on the network are DHCP. But as an
> experiment, I temporarily changed the inside addresses on the whole
> network from 192.168.0.X to 10.0.0.X. Like before, everything is
> fine until these Mac/iPhone devices are turned on. Then everyone gets
> the "there is an IP address conflict" popup again and traffic stops.
>
> If we assume that, say, the Mac isn't DHCP and has an address programmed
> into its stack (I'll go check it myself,) why would there be an IP address
> conflict reported even on the new subnet? If, say, the Mac had
> 192.168.0.1
> programmed into its stack, how would it conflict with any 10.0.0.X
> address?
>
> Thanks.
>
>


From: smlunatick on 17 Apr 2008 12:47
On Apr 16, 7:48 pm, "Janet" <ja...(a)nospam.com> wrote:
> Here's a head scratcher:
>
> We've got three Cisco Aironet AP's connected to a Cisco managed switch
> and everything was working fine until someone brought their iPhone and
> Mac in.  When they turn them on, the other wireless clients get the "there
> is
> an IP address conflict" popup over the system tray and traffic on the
> network
> becomes erratic or stops.
>
> As far as I know, all the devices on the network are DHCP.  But as an
> experiment, I temporarily changed the inside addresses on the whole
> network from 192.168.0.X to 10.0.0.X. Like before, everything is
> fine until these Mac/iPhone devices are turned on.  Then everyone gets
> the "there is an IP address conflict" popup again and traffic stops.
>
> If we assume that, say, the Mac isn't DHCP and has an address programmed
> into its stack (I'll go check it myself,) why would there be an IP address
> conflict reported even on the new subnet?  If, say, the Mac had 192.168.0.1
> programmed into its stack, how would it conflict with any 10.0.0.X address?
>
> Thanks.

The problem is that the iPhone is also a "wireless" device which can
be set with an IP address that is used on your network. You must have
a few IP addresses that might not be "changed" to 10.0.0.xx.
Routers / AP , printers / print servers and servers do not usually use
DHCP assigned addresses.

Or the iPhone is also behaving as a DHCP "server" assigning IP
addresses. It could over lap your network.
From: Janet on 17 Apr 2008 19:12

"John" <a> wrote in message news:e5EWH8BoIHA.5836(a)TK2MSFTNGP04.phx.gbl...

> You sure got me scratching my head. My wild guess is the subnet is too
> small (there are more devices than available IPs)? Or the DHCP (Cisco
> Aironet?) needs a bug fix? Does it have the latest firmware?

The problem was isolated to the Mac computer. When I asked the user if
it was programmed for DHCP, he said he "wasn't sure" and he'd "check it
out." There hasn't been any trouble since then. I still can't understand
how
even a machine with a static IP programmed into it could conflict with any
of
our other DHCP devices even after changing the IP addressing scheme
to a different subnet!


From: Janet on 17 Apr 2008 19:12
I understand about the iPhone. That's why I mentioned it.

There are three items on the network that are assigned a static IP address:
the managed switch, the DSL router and one computer. During the
troubleshooting, I changed all of these to different addresses in the
original
subnet 192.168.0 as well as the new one 10.0.0, yet the "conflicting IP"
popup returned. So that doesn't explain it. Also, the DHCP table of
assigned IP's never showed any conflicts. The DHCP server can hand
out 200 addresses (far more than we'll use) and all the devices with static
assignments are outside this range, of course.

I understand what you're saying about a "rogue" DHCP server on the
network. However, how would that explain the "conflict" popups
after the subnet change from 198 to 10? In other words, how could
this second DHCP server decide to begin assigniong 10. addresses
after I changed the network numbering scheme?

The problem was isolated to a Mac computer. I asked the user if
it was programmed for DHCP. He said he "wasn't sure" and he'd
"check it out." There hasn't been any trouble since then.

I suppose this will be one of those mysteries that I'll take to
my grave unsolved.


"smlunatick" <yveslec(a)gmail.com> wrote in message
news:dcbefb3b-9f92-470c-8384-d5437bd33106(a)24g2000hsh.googlegroups.com...

The problem is that the iPhone is also a "wireless" device which can
be set with an IP address that is used on your network. You must have
a few IP addresses that might not be "changed" to 10.0.0.xx.
Routers / AP , printers / print servers and servers do not usually use
DHCP assigned addresses.

Or the iPhone is also behaving as a DHCP "server" assigning IP
addresses. It could over lap your network.


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